AMD AM79C940KC/W Media access controller for ethernet (maceâ ¢) Datasheet

FINAL
Am79C940
Media Access Controller for Ethernet (MACE™)
DISTINCTIVE CHARACTERISTICS
■ Integrated Controller with Manchester
encoder/decoder and 10BASE-T transceiver
and AUI port
■ Arbitrary byte alignment and little/big endian
memory interface supported
■ Supports IEEE 802.3/ANSI 8802-3 and Ethernet
standards
■ External Address Detection Interface (EADI)
for external hardware address filtering in
bridge/router applications
■ 84-pin PLCC and 100-pin PQFP Packages
■ Internal/external loopback capabilities
■ 80-pin Thin Quad Flat Pack (TQFP) package
available for space critical applications such as
PCMCIA
■ JTAG Boundary Scan (IEEE 1149.1) test access
port interface for board level production test
■ Modular architecture allows easy tuning to
specific applications
■ Digital Attachment Interface (DAI) allows
by-passing of differential Attachment Unit
Interface (AUI)
■ High speed, 16-bit synchronous host system
interface with 2 or 3 cycles/transfer
■ Individual transmit (136 byte) and receive (128
byte) FlFOs provide increase of system latency
and support the following features:
■ Integrated Manchester Encoder/Decoder
■ Supports the following types of network
interface:
— AUI to external 10BASE2, 10BASE5 or
10BASE-F MAU
— Automatic retransmission with no FIFO
reload
— DAI port to external 10BASE2, 10BASE5,
10BASE-T, 10BASE-F MAU
— Automatic receive stripping and transmit
padding (individually programmable)
— General Purpose Serial Interface (GPSI) to
external encoding/decoding scheme
— Automatic runt packet rejection
— Internal 10BASE-T transceiver with
automatic selection of 10BASE-T or AUI port
— Automatic deletion of collision frames
— Automatic retransmission with no FIFO
reload
■ Direct slave access to all on board
configuration/status registers and transmit/
receive FlFOs
■ Direct FIFO read/write access for simple
interface to DMA controllers or l/O processors
■ Sleep mode allows reduced power consumption for critical battery powered applications
■ 5 MHz-25 MHz system clock speed
■ Support for operation in industrial temperature
range (–40°C to +85°C) available in all three
packages
GENERAL DESCRIPTION
The Media Access Controller for Ethernet (MACE) chip
is a CMOS VLSI device designed to provide flexibility
in customized LAN design. The MACE device is specifically designed to address applications where multiple
I/O peripherals are present, and a centralized or system specific DMA is required. The high speed, 16-bit
synchronous system interface is optimized for an external DMA or I/O processor system, and is similar to
many existing peripheral devices, such as SCSI and
serial link controllers.
The MACE device is a slave register based peripheral.
All transfers to and from the system are performed
using simple memory or I/O read and write commands.
In conjunction with a user defined DMA engine, the
MACE chip provides an IEEE 802.3 interface tailored
to a specific application. Its superior modular architecture and versatile system interface allow the MACE
device to be configured as a stand-alone device or
as a connectivity cell incorporated into a larger,
integrated system.
Publication# 16235 Rev: E Amendment/0
Issue Date: May 2000
The MACE device provides a complete Ethernet node
solution with an integrated 10BASE-T transceiver, and
supports up to 25-MHz system clocks. The MACE
device embodies the Media Access Control (MAC)
and Physical Signaling (PLS) sub-layers of the IEEE
802.3 standard, and provides an IEEE defined Attachment Unit Interface (AUI) for coupling to an external
Medium Attachment Unit (MAU). The MACE device is
compliant with 10BASE2, 10BASE5, 10BASE-T, and
10BASE-F transceivers.
Additional features also enhance over-all system
design. The individual transmit and receive FIFOs
optimize system overhead, providing substantial
latency during packet transmission and reception, and
minimizing intervention during normal network error
recovery. The integrated Manchester encoder/decoder
eliminates the need for an external Serial Interface
Adapter (SIA) in the node system. If support for an
external encoding/decoding scheme is desired, the
General Purpose Serial Interface (GPSI) allows direct
access to/from the MAC. In addition, the Digital Attachment Interface (DAI), which is a simplified electrical
attachment specification, allows implementation of
MAUs that do not require DC isolation between the
MAU and DTE. The DAI port can also be used to
indicate transmit, receive, or collision status by
connecting LEDs to the port. The MACE device also
provides an External Address Detection Interface
(EADI) to allow external hardware address filtering in
internet working applications.
2
The Am79C940 MACE chip is offered in a Plastic
Leadless Chip Carrier (84-pin PLCC), a Plastic Quad
Flat Package (100-pin PQFP), and a Thin Quad Flat
Package (TQFP 80-pin). There are several small functional and physical differences between the 80-pin
TQFP and the 84-pin PLCC and 100-pin PQFP configurations. Because of the smaller number of pins in the
TQFP configuration versus the PLCC configuration,
four pins are not bonded out. Though the die is identical
in all three package configurations, the removal of
these four pins does cause some functionality differences between the TQFP and the PLCC and PQFP
configurations. Depending on the application, the
removal of these pins will or will not have an effect.
(See section: “Pins Removed for TQFP Package and
Their Effects.)
With the rise of embedded networking applications operating in harsh environments where temperatures
may exceed the normal commercial temperature (0°C
to +70°C) window, an industrial temperature (-40°C to
+85°C) version is available in all three packages; 84pin PLCC, 100-pin PQFP and 80-pin TQFP. The industrial temperature version of the MACE Ethernet controller is characterized across the industrial temperature
range (-40° C to +85°C) within the published power
supply specification (4.75 V to 5.25 V; i.e., ±5% VCC).
Thus, conformance of MACE performance over this
temperature range is guaranteed by the design and
characterization monitor.
Am79C940
BLOCK DIAGRAM
XTAL1
XTAL2
DXCVR
CLSN
EADI
Port
Control
DBUS 15–0
ADD 4–0
R/W
CS
FDS
DTV
EOF
RDTREQ
TDTREQ
BE 1–0
INTR
SCLK
EDSEL
TC
SLEEP
RESET
RCV FIFO
XMT FIFO
Bus
Interface
Unit
802.3
MAC
Core
TCK
EADI Port
DO±
DI±
CI±
AUI
10BASE-T
FIFO
Control
10BASE-T
MAU
TXD±
TXP±
RXD
LNKST
RXPOL
Command
& Status
Registers
DAI
Port
TXDAT±
TXEN
RXDAT
RXCRS
DAI Port
GPSI
Port
STDCLK
TXDAT+
TXEN
SRDCLK
RXDAT
RXCRS
CLSN
GPSI
JTAG
PORT CNTRL
TDI
AUI
Port
SRDCLK
SRD
SF/BD
EAM/R
C16235D-1
TDO
TMS
Notes:
1. Only one of the network ports AUI, 10BASE-T, DAI port or GPSI can be active at any time. Some shared signals are
active regardless of which network port is active, and some are reconfigured.
2. The EADI port is active at all times.
Am79C940
3
TABLE OF CONTENTS
AM79C940 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
DISTINCTIVE CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
TABLE OF CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
CONNECTION DIAGRAMS PL 084 PLCC PACKAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
CONNECTION DIAGRAMS PQR100 PQFP PACKAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
CONNECTION DIAGRAMS PQT080 TQFP PACKAGE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
ORDERING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Standard Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
PIN/PACKAGE SUMMARY (PLCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
PIN DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Network Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Attachment Unit Interface (AUI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
CI+/CI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
DI+/DI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
DO+/DO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Digital Attachment Interface (DAI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
TXDAT+/TXDAT–. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
TXEN/TXEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Transmit Enable (Output) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
RXDAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
RXCRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
DXCVR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
10BASE-T INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
TXD+, TXD– . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
TXP+, TXP–. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
RXD+, RXD– . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
LNKST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
RXPOL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
General Purpose Serial Interface (GPSI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
STDCLK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
CLSN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
External Address Detection Interface (EADI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
SF/BD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
SRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
EAM/R . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
SRDCLK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
HOST SYSTEM INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
DBUS15-0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
ADD4-0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
R/W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
RDTREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
TDTREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
FDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
DTV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
EOF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
BE1–0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
CS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
INTR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
RESET. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
SCLK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
EDSEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
TC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
IEEE 1149.1 TEST ACCESS PORT (TAP) INTERFACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
TCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
4
Am79C940
TMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
TDI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
TDO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
GENERAL INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
XTAL1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
XTAL2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
SLEEP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
DVDD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
DVSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
AVDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
AVSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
PIN FUNCTIONS NOT AVAILABLE WITH THE 80-PIN TQFP PACKAGE . . . . . . . . . . . . . . . . . .28
PINS REMOVED FOR TQFP PACKAGE AND THEIR EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . .28
FUNCTIONAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Network Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
System Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
DETAILED FUNCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Block Level Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Bus Interface Unit (BIU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
BIU to FIFO Data Path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Byte Alignment For FIFO Read Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
BIU to Control and Status Register Data Path. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
FIFO Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Media Access Control (MAC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Manchester Encoder/Decoder (MENDEC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Attachment Unit Interface (AUI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Digital Attachment Interface (DAI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
10BASE-T Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Twisted Pair Transmit Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Twisted Pair Receive Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Link Test Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Polarity Detection and Reversal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Twisted Pair Interface Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Collision Detect Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Signal Quality Error (SQE) Test (Heartbeat) Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Jabber Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
External Address Detection Interface (EADI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
Internal/External Address Recognition Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
General Purpose Serial Interface (GPSI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
IEEE 1149.1 Test Access Port Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
SLAVE ACCESS OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
Read Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
Write Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Reinitialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
TRANSMIT OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Transmit FIFO Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Transmit Function Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Automatic Pad Generation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
Transmit FCS Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Transmit Status Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Transmit Exception Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
RECEIVE OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
Receive FIFO Read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
Receive Function Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
Automatic Pad Stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Receive FCS Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Am79C940
5
Receive Status Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Receive Exception Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
LOOPBACK OPERATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
USER ACCESSIBLE REGISTERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
8-Bit Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
Programmer’s Register Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
Missing Table Title? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
SYSTEM APPLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
Host System Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
NETWORK INTERFACES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
External Address Detection Interface (EADI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
MACE Compatible AUI Isolation Transformers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
MANUFACTURER CONTACT INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89
ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
OPERATING RANGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
Commercial (C) Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
Industrial (I) Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
VCC Supply Voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90
DC CHARACTERISTICS (UNLESS OTHERWISE NOTED, PARAMETRIC VALUES ARE THE SAME
BETWEEN COMMERCIAL DEVICES AND INDUSTRIAL DEVICES.) . . . . . . . . . . . . . . . . . . . . . . .90
AC CHARACTERISTICS (UNLESS OTHERWISE NOTED, PARAMETRIC VALUES ARE THE SAME
BETWEEN COMMERCIAL DEVICES AND INDUSTRIAL DEVICES.) . . . . . . . . . . . . . . . . . . . . . . .93
KEY TO SWITCHING WAVEFORMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97
SWITCHING TEST CIRCUITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
PHYSICAL DIMENSIONS* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117
PL 084 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
84-Pin Plastic Leaded Chip Carrier (measured in inches) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
PHYSICAL DIMENSIONS* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118
PQR100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
100-Pin Plastic Quad Flat Pack; Trimmed and Formed (measured in millimeters) . . . . . . . . . . . 118
PHYSICAL DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119
PQR100 100-Pin Plastic Quad Flat Pack with Molded Carrier Ring (measured in millimeters) . 119
PHYSICAL DIMENSIONS* PQT080 80-Pin Thin Quad Flat Package (measured in millimeters)120
LOGICAL ADDRESS FILTERING FOR ETHERNET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
BSDL DESCRIPTION OF AM79C940 MACE JTAG STRUCTURE . . . . . . . . . . . . . . . . . . . . . . . . .123
AM79C940 MACE REV C0 SILICON ERRATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
6
Am79C940
RXCRS
RXDAT
CLSN
TXEN/ TXEN
STDCLK
DVSS
TXDATTXDAT+
DVSS
EDSEL
DXCVR
DVDD
AVDD
CI+
CIDI+
DIAVDD
DO+
DOAV SS
CONNECTION DIAGRAMS
PL 084
PLCC PACKAGE
11 10 9 8 7 6 5 4 3 2 1 84 83 82 81 80 79 78 77 76 75
12
74
73
13
72
14
71
15
70
16
69
17
68
18
67
19
66
20
Am79C940JC
65
21
MACE
64
22
63
23
62
24
61
25
60
26
59
27
58
28
57
29
56
30
55
31
54
32
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53
XTAL2
AVSS
XTAL1
AVDD
TXD+
TXP+
TXDTXPAVDD
RXD+
RXDDVDD
TDI
DVSS
TCK
TMS
TDO
LNKST
RXPOL
CS
R/W
DBUS10
DBUS11
DBUS12
DBUS13
DV DD
DBUS14
DBUS15
DV SS
EOF
DTV
FDS
BE0
BE1
SCLK
TDTREQ
RDTREQ
ADD0
ADD1
ADD2
ADD3
ADD4
SRDCLK
EAM/R
SRD
SF/BD
RESET
SLEEP
DVDD
INTR
TC
DBUS0
DVSS
DBUS1
DBUS2
DBUS3
DBUS4
DVSS
DBUS5
DBUS6
DBUS7
DBUS8
DBUS9
16235D-2
Am79C940
7
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
RXCRS
RXDAT
CLSN
TXEN/TXEN
STDCLK
DVSS
TXDATTXDAT+
DVSS
EDSEL
DXCVR
DVDD
AVDD
CI+
CIDI+
DIAVDD
DO+
DO-
CONNECTION DIAGRAMS
PQR100
PQFP PACKAGE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
MACE
Am79C940KC
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
NC
AVSS
NC
NC
NC
XTAL2
AVSS
XTAL1
AVDD
TXD+
TXP+
TXD
TXP
AVDD
RXD+
RXD
DVDD
TDI
DVSS
TCK
TMS
TDO
LNKST
RXPOL
CS
R/W
NC
NC
NC
NC
DBUS11
DBUS12
DBUS13
DVDD
DBUS14
DBUS15
DVSS
EOF
DTV
FDS
BE0
BE1
SCLK
TDTREQ
RDTREQ
ADD0
ADD1
ADD2
ADD3
ADD4
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
NC
NC
NC
NC
SRDCLK
EAM/R
SRD
SF/BD
RESET
SLEEP
DVDD
INTR
TC
DBUS0
DVSS
DBUS1
DBUS2
DBUS3
DBUS4
DVSS
DBUS5
DBUS6
DBUS7
DBUS8
DBUS9
NC
NC
NC
DBUS10
NC
16235D-3
8
Am79C940
EDSEL
DXCVR
DVDD
AVDD
CI+
CIDI+
DIAVDD
DO+
DOAVSS
RXCRS
RXDAT
CLSN
TXEN/
STDCLK
DVSS
TXDAT+
DVSS
CONNECTION DIAGRAMS
PQT080
TQFP PACKAGE
80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61
SRDCLK
EAM/R
SF/BD
RESET
SLEEP
DVDD
INTR
TC
DBUS0
DV SS
DBUS1
DBUS2
DBUS3
DBUS4
DV SS
DBUS5
DBUS6
DBUS7
DBUS8
DBUS9
1
2
3
4
5
6
60
59
58
57
56
55
7
8
9
10
11
12
13
14
15
16
17
18
19
20
54
53
52
51
50
49
48
47
46
45
44
43
42
41
MACE
Am79C940VC
XTAL2
AVSS
XTAL1
AVDD
TXD+
TXP+
TXDTXPAVDD
RXD+
RXDDVDD
TDI
DVSS
TCK
TMS
TD0
LNKST
CS
R/W
DBUS10
DBUS11
DBUS12
DBUS13
DVDD
DBUS14
DBUS15
DV SS
EOF
FDS
BE0
BE1
SCLK
TDTREQ
RDTREQ
ADD0
ADD1
ADD2
ADD3
ADD4
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
16235D-4
Notes: Four pin functions available on the PLCC and PQFP packages are not available with the TQFP package.
(See full data sheet for description of pins not included with the 80-pin TQFP package. In particular, see section
“Pin Functions not available with the 80-pin TQFP package.”)
Am79C940
9
ORDERING INFORMATION
Standard Products
AMD standard products are available in several packages and operating ranges. The order number (Valid Combination) is formed
by a combination of:
AM79C940
V
C
\W
ALTERNATE PACKAGING OPTION
\W = Trimmed and Formed in a Tray
OPTIONAL PROCESSING
Blank = Standard Processing
TEMPERATURE RANGE
C = Commercial (0° to +70°C)
I = Industrial (-40°C to +85°C)
PACKAGE TYPE (per Prod. Nomenclature/16-038)
J = 84-Pin Plastic Leaded Chip Carrier (PL 084)
K = 100-Pin Plastic Quad Flat Pack (PQR100)
V = 80-Pin Thin Quad Flat Package (PQT080)
SPEED
Not Applicable
DEVICE NUMBER/DESCRIPTION (include revision letter)
Am79C940
Media Access Controller for Ethernet
Valid Combinations
Valid Combinations
AM79C940
JC, KC,
KC\W, VC,
VC\W
AM79C940
JI, KI,
KI\W, VI,
VI\W
The Valid Combinations table lists configurations planned to
be supported in volume for this device. Consult the local AMD
sales office to confirm availability of specific valid
combinations and to check on newly released combinations.
Note:
Currently the silicon revision level of the MACE Ethernet controller is revision C0. This is designated by the marking on the package
as Am79C940Bxx, where “xx” indicate package type and temperature range.
10
Am79C940
PIN/PACKAGE SUMMARY (PLCC)
PLCC Pin #
Pin Name
1
DXCVR
Disable Transceiver
2
EDSEL
Edge Select
3
DVSS
4
TXDAT+
5
TXDAT–
6
DVSS
7
STDCLK
8
TXEN/TXEN
9
CLSN
10
RXDAT
Pin Function
Digital Ground
Transmit Data +
Transmit Data –
Digital Ground
Serial Transmit Data Clock
Transmit Enable
Collision
Receive Data
11
RXCRS
Receive Carrier Sense
12
SRDCLK
Serial Receive Data Clock
13
EAM/R
14
SRD
External Address Match/Reject
Serial Receive Data
15
SF/BD
Start Frame/Byte Delimiter
16
RESET
Reset
17
SLEEP
Sleep Mode
18
DVDD
Digital Power
19
INTR
Interrupt
20
TC
21
DBUS0
22
DVSS
23
DBUS1
Data Bus1
24
DBUS2
Data Bus2
25
DBUS3
Data Bus3
26
DBUS4
Data Bus4
Timing Control
Data Bus0
Digital Ground
Digital Ground
27
DVSS
28
DBUS5
Data Bus5
29
DBUS6
Data Bus6
30
DBUS7
Data Bus7
31
DBUS8
Data Bus8
32
DBUS9
Data Bus9
33
DBUS10
Data Bus10
34
DBUS11
Data Bus11
35
DBUS12
Data Bus12
36
DBUS13
Data Bus13
Digital Power
37
DVDD
38
DBUS14
Data Bus14
39
DBUS15
Data Bus15
40
DVSS
Digital Ground
41
EOF
End Of Frame
42
DTV
Data Transfer Valid
43
FDS
FIFO Data Strobe
44
BE0
Byte Enable0
Am79C940
11
PIN/PACKAGE SUMMARY (continued)
12
PLCC Pin #
Pin Name
Pin Function
45
BE1
Byte Enable 1
46
SCLK
System Clock
47
TDTREQ
Transmit Data Transfer Request
48
RDTREQ
Receive Data Transfer Request
49
ADD0
Address0
50
ADD1
Address1
51
ADD2
Address2
52
ADD3
Address3
53
ADD4
Address4
54
R/W
Read/Write
55
CS
Chip Select
56
RXPOL
Receive Polarity
57
LNKST
Link Status
58
TDO
Test Data Out
59
TMS
Test Mode Select
60
TCK
Test Clock
61
DVSS
Digital Ground
62
TDI
Test Data Input
63
DVDD
Digital Power
64
RXD–
Receive Data–
65
RXD+
Receive Data+
66
AVDD
Analog Power
67
TXP–
Transmit Pre-distortion
68
TXD–
Transmit Data–
69
TXP+
Transmit Pre-distortion+
70
TXD+
Transmit Data+
71
AVDD
Analog Power
72
XTAL1
Crystal Output
73
AVSS
Analog Ground
74
XTAL2
Crystal Output
75
AVSS
Analog Ground
76
DO–
Data Out–
77
DO+
Data Out+
78
AVDD
Analog Power
79
DI–
Data In–
80
DI+
Data In+
81
CI–
Control In–
82
CI+
Control In+
83
AVDD
Analog Power
84
DVDD
Digital Power
Am79C940
PIN/PACKAGE SUMMARY (PQFP) (continued)
PQFP Pin #
Pin Name
Pin Function
1
NC
No Connect
2
NC
No Connect
3
NC
No Connect
4
NC
No Connect
5
SHDCLK
6
EAM/R
Serial Receive Data Clock
External Address Match/Reject
7
SRD
8
SF/BD
Serial Receive Data
Start Frame/Byte Delimiter
9
RESET
Reset
10
SLEEP
Sleep Mode
11
DVDD
Digital Power
12
INTR
Interrupt
13
TC
14
DBUS0
Timing Control
Data Bus0
Digital Ground
15
DVSS
16
DBUS1
Data Bus1
17
DBUS2
Data Bus2
18
DBUS3
Data Bus3
19
DBUS4
Data Bus4
20
Digital Ground
21
DVSS
DBUS5
22
DBUS6
Data Bus6
23
DBUS7
Data Bus7
24
DBUS8
Data Bus8
25
DBUS9
Data Bus9
26
NC
No Connect
27
NC
No Connect
28
NC
No Connect
29
DBUS10
Data Bus10
30
NC
No Connect
31
DBUS11
Data Bus11
32
DBUS12
Data Bus12
33
DBUS13
Data Bus13
34
DVDD
35
DBUS14
Data Bus14
36
DBUS15
Data Bus15
37
38
DVSS
EOF
39
DTV
Data Transfer Valid
40
FDS
FIFO Data Strobe
41
BE0
Byte Enable0
42
BE1
Byte Enable1
Data Bus5
Digital Power
Digital Ground
End of Frame
Am79C940
13
PIN/PACKAGE SUMMARY (continued)
14
PQFP Pin #
Pin Name
Pin Function
43
SCLK
44
TDTREQ
Transmit Data Transfer Request
45
RDTREQ
Receive Data Transfer Request
46
ADD0
Address0
47
ADD1
Address1
48
ADD2
Address2
49
ADD3
Address3
50
ADD4
Address4
51
NC
No Connect
52
NC
No Connect
53
NC
No Connect
54
NC
No Connect
55
R/W
Read/Write
56
CS
Chip Select
57
RXPOL
Receive Polarity
58
LNKST
Link Status
59
TDO
Test Data Out
60
TMS
Test Mode Select
61
TCK
Test Clock
62
DVSS
Digital Ground
63
TDI
Test Data Input
64
DVDD
System Clock
Digital Power
65
RXD–
Receive Data–
66
RXD+
Receive Data+
67
AVDD
Analog Power
68
TXP–
Transmit Pre-distortion–
69
TXD–
Transmit Data–
70
TXP+
Transmit Pre-distortion+
71
TXD+
Transmit Data+
72
AVDD
Analog Power
73
XTAL1
74
AVSS
Analog Ground
75
XTAL2
Crystal Output
76
NC
No Connect
77
NC
No Connect
78
NC
No Connect
79
AVSS
80
NC
Crystal Input
Analog Ground
No Connect
81
DO–
Data Out–
82
DO+
Data Out+
83
AVDD
Analog Power
84
DI–
Data In–
85
DI+
Data In+
Am79C940
PIN/PACKAGE SUMMARY (continued)
PQFP Pin #
Pin Name
Pin Function
86
CI–
Control In–
87
CI+
Control In+
88
AVDD
Analog Power
89
DVDD
Digital Power
90
DXCVR
Disable Transceiver
91
EDSEL
Edge Select
Digital Ground
92
DVSS
93
TXDAT+
Transmit Data +
94
TXDAT–
Transmit Data–
95
DVSS
Digital Ground
96
STDCLK
97
TXEN/TXEN
Serial Transmit Data Clock
98
CLSN
99
RXDAT
Receive Data
100
RXCRS
Receive Carrier Sense
Transmit Enable
Collision
Am79C940
15
PIN/PACKAGE SUMMARY (TQFP) (continued)
16
TQFP
Pin Number
Pin Name
Serial Receive Data Clock
41
R/W
Read/Write
EAM/R
External Address Match/Reject
42
CS
Chip/Select
3
SF/BD
Start Frame/Byte Delimiter
43
LNKST
Link Status
4
RESET
Reset
44
TDO
Test Data Out
5
SLEEP
Sleep Mode
45
TMS
Test Mode Select
6
DVDD
Digital Power
46
TCK
Text Clock
7
INTR
Interrupt
47
DVSS
Digital Ground
8
TC
Timing Control
48
TDI
Test Data Input
9
DBUS0
Data Bus0
49
DVDD
Digital Power
10
DVSS
Digital Ground
50
RXD–
Receive Data–
11
DBUS1
Data Bus1
51
RXD+
Receive Data+
12
DBUS2
Data Bus2
52
AVDD
Analog Power
13
DBUS3
Data Bus3
53
TXP–
Transmit Pre-distortion–
14
DBUS4
Data Bus4
54
TXD–
Transmit Data–
15
DVSS
Digital Ground
55
TXP+
Transmit Pre-distortion+
16
DBUS5
Data Bus5
56
TXD+
Transmit Data+
17
DBUS6
Data Bus6
57
AVDD
Analog Power
18
DBUS7
Data Bus7
58
XTAL1
Crystal Output
19
DBUS8
Data Bus8
59
AVSS
Analog Ground
20
DBUS9
Data Bus9
60
XTAL2
Crystal Output
21
DBUS10
Data Bus10
61
AVSS
Analog Ground
22
DBUS11
Data Bus11
62
DO–
Data Out–
23
DBUS12
Data Bus12
63
DO+
Data Out+
24
DBUS13
Data Bus13
64
AVDD
25
DVDD
Digital Power
65
DI–
Data In–
26
DBUS14
Data Bus14
66
DI+
Data Out+
27
DBUS15
Data Bus15
67
CI–
Control In–
28
DVSS
Digital Ground
68
CI+
Control In+
29
EOF
End of Frame
69
AVDD
Analog Power
30
FDS
FIFO Data Strobe
70
DVDD
Digital Power
31
BE0
Byte Enable0
71
DXCVR
Disable Transceiver
32
BE1
Byte Enable1
72
EDSEL
Edge Select
33
SCLK
System Clock
73
DVSS
Digital Ground
34
TDTREQ
Transmit Data Transfer Request
74
TXDAT+
Transmit Data+
35
RDTREQ
Receive Data Transfer Request
75
DVSS
Digital Ground
36
ADD0
Address0
76
STDCLK
37
ADD1
Address1
77
TXEN/TXEN
38
ADD2
Address2
78
CLSN
39
ADD3
Address3
79
RXDAT
Receive Data
40
ADD4
Address4
80
RXCRS
Receive Carrier Sense
TQFP #
Pin Name
1
SRDCLK
2
Pin Function
Am79C940
Pin Function
Analog Power
Serial Transmit Data Clock
Transmit Enable
Collision
PIN SUMMARY
Pin Name
Pin Function
Type
Active
Comment
Attachment Unit Interface (AUI)
DO+/DO–
Data Out
O
Pseudo-ECL
DI+/DI–
Data In
I
Pseudo-ECL
CI+/CI–
Control In
I
Pseudo-ECL
RXCRS
Receive Carrier Sense
I/O
High
TTL output. Input in DAI, GPSI port
TXEN
Transmit Enable
O
High
TTL. TXEN in DAI port
CLSN
Collision
I/O
High
TTL output. Input in GPSI
DXCVR
Disable Transceiver
O
Low
TTL low
STDCLK
Serial Transmit Data Clock
I/O
Output. Input in GPSI
SRDCLK
Serial Receive Data Clock
I/O
Output. Input in GPSI
Digital Attachment Interface (DAI)
TXDAT+
Transmit Data +
O
High
TTL. See also GPSI
TXDAT–
Transmit Data–
O
Low
TTL
TXEN
Transmit Enable
O
Low
TTL. See TXEN in GPSI
RXDAT
Receive Data
RXCRS
Receive Carrier Sense
I/O
High
TTL input. Output in AUI
CLSN
Collision
I/O
High
TTL output. Input in GPSI
DXCVR
Disable Transceiver
O
High
TTL high
STDCLK
Serial Transmit Data Clock
I/O
Output. Input in GPSI
SRDCLK
Serial Receive Data Clock
I/O
Output. Input in GPSI
I
TTL. See also GPSI
10BASE-T Interface
TXD+/TXD–
Transmit Data
O
TXP+/TXP–
Transmit Pre-distortion
O
RXD+/RXD–
Receive Data
I
LNKST
Link Status
O
Low
Open Drain
RXPOL
Receive Polarity
O
Low
Open Drain
TXEN
Transmit Enable
O
High
TTL. TXEN in DAI port
RXCRS
Receive Carrier Sense
I/O
High
TTL output. Input in DAI, GPSI port
CLSN
Collision
I/O
High
TTL output. Input in GPSI
DXCVR
Disable Transceiver
O
High
TTL high
STDCLK
Serial Transmit Data Clock
I/O
Output. Input in GPSI
SRDCLK
Serial Receive Data Clock
I/O
Output. Input in GPSI
I/O
Input
General Purpose Serial Interface (GPSI)
STDCLK
Serial Transmit Data Clock
TXDAT+
Transmit Data +
O
High
TTL. See also DAI port
TXEN
Transmit Enable
O
High
TTL. TXEN in DAI port
SRDCLK
Serial Receive Data Clock
I/O
RXDAT
Receive Data
RXCRS
Receive Carrier Sense
I/O
High
TTL input. Output in AUI
CLSN
Collision
I/O
High
TTL input
DXCVR
Disable Transceiver
O
Low
TTL low
Input. See also EADI port
I
Am79C940
TTL. See also DAI port
17
PIN SUMMARY (continued)
Pin Name
Pin Function
Type
Active
Comment
External Address Detection Interface (EADI)
SF/BD
Start Frame/Byte Delimiter
O
High
SRD
Serial Receive Data
O
High
EAM/R
External Address Match/Reject
I
Low
SRDCLK
Serial Receive Data Clock
I/O
Output except in GPSI
Host System Interface
DBUS 15–0
Data Bus
I/O
High
ADD4–0
Address
I
High
R/W
Read/Write
I
High/Low
RDTREQ
Receive Data Transfer Request
O
Low
TDTREQ
Transmit Data Transfer Request
O
Low
DTV
Data Transfer Valid
O
Low
EOF
End Of Frame
I/O
Low
BE0
Byte Enable 0
I
Low
BE1
Byte Enable 1
I
Low
CS
Chip Select
I
Low
FDS
FIFO Data Strobe
I
Low
INTR
Interrupt
O
Low
EDSEL
Edge Select
I
High
TC
Timing Control
I
Low
SCLK
System Clock
I
High
RESET
Reset
I
Low
Tristate
Open Drain
Internal pull-up
IEEE 1149.1 Test Access Port (TAP) Interface
TCK
Test Clock
I
Internal pull-up
TMS
Test Mode Select
I
Internal pull-up
TDI
Test Data Input
I
Internal pull-up
TDO
Test Data Out
O
General Interface
XTAL1
Crystal Input
I
CMOS
XTAL2
Crystal Output
O
CMOS
SLEEP
Sleep Mode
I
DVDD
Digital Power (4 pins)
P
DVSS
Digital Power (6 pins)
P
AVDD
Analog Power (4 pins)
P
AVSS
Analog Power (2 pins)
P
18
Am79C940
Low
TTL
PIN DESCRIPTION
Network Interfaces
DI+/DI
Data In (Input)
The MACE device has five potential network interfaces. Only one of the interfaces that provides physical
network attachment can be used (active) at any time.
Selection between the AUI, 10BASE-T, DAI or GPSI
ports is provided by programming the PHY Configuration Control register. The EADI port is effectively active
at all times. Some signals, primarily used for status
reporting, are active for more than one single interface
(the CLSN pin for instance). Under each of the descriptions for the network interfaces, the primary signals
which are unique to that interface are described.
Where signals are active for multiple interfaces, they
are described once under the interface most appropriate.
Attachment Unit Interface (AUI)
CI+/CI
Control In (Input)
A differential input pair, signaling the MACE device that
a collision has been detected on the network media, indicated by the CI± inputs being exercised with 10 MHz
pattern of sufficient amplitude and duration. Operates
at pseudo-ECL levels.
A differential input pair to the MACE device for receiving Manchester encoded data from the network.
Operates at pseudo-ECL levels.
DO+/DO
Data Out (Output)
A differential output pair from the MACE device for
transmitting Manchester encoded data to the network.
Operates at pseudo-ECL levels.
Digital Attachment Interface (DAI)
TXDAT+/TXDAT–
Transmit Data (Output)
When the DAI port is selected, TXDAT± are configured
as a complementary pair for Manchester encoded data
output from the MACE device, used to transmit data to
a local external network transceiver. During valid transmission (indicated by TXEN low), a logical 1 is indicated by the TXDAT+ pin being in the high state and
TXDAT– in the low state; and a logical 0 is indicated by
the TXDAT+ pin being in the low state and TXDAT– in
the high state. During idle (TXEN high), TXDAT+ will be
in the high state, and TXDAT– in the low state. When
the GPSI port is selected, TXDAT+ will provide NRZ
data output from the MAC core, and TXDAT– will be
held in the LOW state. Operates at TTL levels. The
operations of TXDAT+ and TXDAT– are defined in the
following tables:
TXDAT + Configuration
SLEEP
0
1
1
1
1
1
PORTSEL
[1-0]
XX
00
01
10
11
XX
ENDPLSIO
X
1
1
1
1
0
Interface Description
Sleep Mode
AUI
10BASE–T
DAI Port
GPSI
Status Disabled
Pin Function
High Impedance
High Impedance (Note 2)
High Impedance (Note 2)
TXDAT+ Output
TXDAT+ Output
High Impedance (Note 2)
TXDAT – Configuration
SLEEP
0
1
1
1
1
1
PORTSEL
[1-0]
XX
00
01
10
11
XX
ENDPLSIO
X
1
1
1
1
0
Interface Description
Sleep Mode
AUI
10BASE–T
DAI Port
GPSI
Status Disabled
Pin Function
High Impedance
High Impedance
High Impedance
TXDAT– Output
LOW
High Impedance
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
Am79C940
19
TXEN/TXEN
Transmit Enable (Output)
decoded data input to the MAC core of the MACE
device, from an external Manchester encoder/decoder.
Operates at TTL levels.
When the AUI port is selected (PORTSEL [1-0] = 00),
an output indicating that the AUI DO± differential output
has valid Manchester encoded data is presented.
When the 10BASE-T port is selected (PORTSEL [1-0]
= 01), indicates that Manchester data is being output
on the TXD±/TXP± complementary outputs. When the
DAI port is selected (PORTSEL [1–0] = 10), indicates
that Manchester data is being output on the DAI port
TXDAT± complementary outputs. When the GPSI port
is selected (PORTSEL [1–0] =11), indicates that NRZ
data is being output from the MAC core of the MACE
device, to an external Manchester encoder/decoder, on
the TXDAT+ output. Active low when the DAI port is
selected, active high when the AUI, 10 BASE-T or
GPSI is selected. Operates at TTL levels.
RXCRS
Receive Carrier Sense (Input/Output)
When the AUI port is selected (PORTSEL [1–0] = 00),
an output indicating that the DI± input pair is receiving
valid Manchester encoded data from the external
transceiver which meets the signal amplitude and
pulse width requirements. When the 10BASE-T port is
selected (PORTSEL [1–0] = 01), an output indicating
that the RXD± input pair is receiving valid Manchester
encoded data from the twisted pair cable which meets
the signal amplitude and pulse width requirements.
RXCRS will be asserted high for the entire duration of
the receive message. When the DAI port is selected
(PORTSEL [1-0] = 10), an input signaling the MACE
device that a receive carrier condition has been
detected on the network, and valid Manchester
encoded data is being presented to the MACE device
on the RXDAT line. When the GPSI port is selected
(PORTSEL [1-0] = 11), an input signalling the internal
MAC core that valid NRZ data is being presented on
the RXDAT input. Operates at TTL levels.
RXDAT
Receive Data (Input)
When the DAI port is selected (PORTSEL [1–0] = 10),
the Manchester encoded data input to the integrated
clock recovery and Manchester decoder of the MACE
device, from an external network transceiver. When the
GPSI port is selected (PORTSEL [1–0] =11), the NRZ
TXEN/TXEN Configuration
SLEEP
PORTSEL
[1-0]
ENDPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
TXEN Output
1
01
1
10BASE-T
TXEN Output
1
10
1
DAI Port
TXEN Output
1
11
1
GPSI
TXEN Output
1
XX
0
Status Disabled
High Impedance (Note 3)
Interface Description
Pin Function
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. When the GPSI port is selected, TXEN should have an external pull-down attached (e.g. 3.3k Ω) to ensure the output is held
inactive before ENPLSIO is set.
3. This pin should be externally terminated, if unused, to reduce power consumption.
20
Am79C940
RXDAT Configuration
SLEEP
PORTSEL
[1–0]
ENPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
High Impedance (Note 2)
1
01
1
10BASE-T
High Impedance (Note 2)
1
10
1
DAI Port
RXDAT Input
1
11
1
GPSI
RXDAT Input
1
XX
0
Status Disabled
High Impedance (Note 2)
Interface Description
Pin Function
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
RXCRS Configuration
SLEEP
PORTSEL
[1-0]
ENDPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
RXCRS Output
1
01
1
10BASE-T
RXCRS Output
1
10
1
DAI Port
RXCRS Output
1
11
1
GPSI
RXCRS Output
1
XX
0
Status Disabled
High Impedance (Note 2)
Interface Description
Pin Function
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
DXCVR
Disable Transceiver (Output)
An output from the MACE device to indicate the network port in use, as programmed by the ASEL bit or the
PORTSEL [1–0] bits. The output is provided to allow
power down of an external DC-to-DC converter, typically used to provide the voltage requirements for an
external 10BASE2 transceiver.
When the Auto Select (ASEL) feature is enabled, the
state of the PORTSEL [1–0] bits is overridden, and the
network interface will be selected by the MACE device,
dependent only on the status of the 10BASE-T link. If
the link is active (LNKST pin driven LOW) the
10BASE-T port will be used as the active network interface. If the link is inactive (LNKST pin pulled HIGH) the
AUI port will be used as the active network interface.
Auto Select will continue to operate even when the
SLEEP pin is asserted if the RWAKE bit has been set.
The AWAKE bit does not allow the Auto Select function, and only the receive section of 10BASE-T port will
be active (DXCVR = HIGH).
Active (HIGH) when either the 10BASE-T or DAI port
is selected. Inactive (LOW) when the AUI or GPSI port
is selected.
Am79C940
21
DXCVR Configuration—SLEEP Operation
Sleep
Pin
RWAKE
Bit
AWAKE
Bit
ASEL
Bit
0
0
0
X
0
1
0
0
0
1
0
0
0
1
0
0
0
1
0
0
0
1
0
1
0
1
0
1
0
1
1
1
0
1
1
0
0
1
LNKST
Pin
PORTSEL
[1–0] Bits
Interface
Description
Pin
Function
Sleep
High
Mode
Impedance
00
AUI with EADI port
LOW
01
10BASE-T with EADI port
HIGH
10
Invalid
HIGH
11
Invalid
LOW
0X
AUI with EADI port
LOW
0X
10BASE-T with EADI port
HIGH
HIGH
0X
AUI with EADI port
LOW
1
LOW
0X
10BASE-T with EADI port
HIGH
X
X
0X
10BASE-T
HIGH
High
Impedance
High
Impedance
High
Impedance
High
Impedance
High
Impedance
High
Impedance
High
Impedance
XX
Note:
1. RWAKE and ASEL are located in the PHY Configuration Control register (REG ADDR 15). PORTSEL [1–0] and ENPLSIO
are located in the PLS Configuration Control register (REG ADDR 14). All bits must be programmed prior to the assertion of
the SLEEP pin.
DXCVR Configuration—Normal Operation
SLEEP
Pin
ASEL
Bit
LNKST
Pin
PORTSEL
[1-0] Bits
ENPLSIO
BIT
Interface
Description
Pin
Function
1
X
X
XX
X
SIA Test Mode
1
0
X
00
X
AUI
LOW
1
0
X
01
X
10BASE-T
HIGH
1
0
X
10
X
DAI port
HIGH
1
0
X
11
X
GPSI
LOW
1
1
HIGH
0X
X
AUI
LOW
1
1
LOW
0X
X
10BASE-T
HIGH
High
Impedance
Note:
1. RWAKE and ASEL are located in the PHY Configuration Control register (REG ADDR 15). PORTSEL [1–0] and ENPLSIO
are located in the PLS Configuration Control register (REG ADDR 14).
22
Am79C940
10BASE-T INTERFACE
TXD+, TXD–
RXPOL
Transmit Data (Output)
The twisted pair receiver is capable of detecting a
receive signal with reversed polarity (wiring error). The
RXPOL pin is normally in the LOW state, indicating
correct polarity of the received signal. If the receiver
detects a received packet with reversed polarity, then
this pin is not driven (requires external pull-up) and the
polarity of subsequent packets are inverted. In the
LOW output state, this pin is capable of sinking a
maximum of 12mA and can be used to drive an LED.
Receive Polarity (Output, Open Drain)
10BASE–T port differential drivers.
TXP+, TXP–
Transmit Pre-Distortion (Output)
Transmit wave form differential driver for pre-distortion.
RXD+, RXD–
Receive Data (Input)
The polarity correction feature can be disabled by
setting the Disable Auto Polarity Correction (DAPC) bit
in the PHY Configuration Control register. In this case,
the Receive Polarity correction circuit is disabled and
the internal receive signal remains non-inverted,
irrespective of the received signal. Note that RXPOL
will continue to reflect the polarity detected by the
receiver.
10BASE–T port differential receiver. These pins should
be externally terminated to reduce power consumption
if the 10BASE–T interface is not used.
LNKST
Link Status (OutputOpen Drain)
This pin is driven LOW if the link is identified as functional. If the link is determined to be nonfunctional, due
to missing idle link pulses or data packets, then this pin
is not driven (requires external pull-up). In the LOW
output state, the pin is capable of sinking a maximum
of 12 mA and can be used to drive an LED.
General Purpose Serial Interface (GPSI)
STDCLK
Serial Transmit Data Clock (Input/Output)
When either the AUI, 10BASE–T or DAI port is
selected, STDCLK is an output operating at one half the
crystal or XTAL1 frequency. STDCLK is the encoding
clock for Manchester data transferred to the output of
either the AUI DO± pair, the 10BASE-T TXD±/TXP±
pairs, or the DAI port TXDAT± pair. When using the
GPSI port, STDCLK is an input at the network data rate,
provided by the external Manchester encode/decoder,
to strobe out the NRZ data presented on the TXDAT+
output. This is also required for internal loopbacks while
in GPSI mode.
This feature can be disabled by setting the Disable Link
Test (DLNKTST) bit in the PHY Configuration Control
register. In this case the internal Link Test Receive
function is disabled, the LNKST pin will be driven LOW,
and the Transmit and Receive functions will remain
active regardless of arriving idle link pulses and data.
The internal 10BASE-T MAU will continue to generate
idle link pulses irrespective of the status of the
DLNKTST bit.
STDCLK Configuration
SLEEP
PORTSEL
[1-0]
ENDPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
STDCLK Output
1
01
1
10BASE-T
STDCLK Output
1
10
1
DAI Port
STDCLK Output
1
11
1
GPSI
STDCLK Output
1
XX
0
Status Disabled
High Impedance (Note 2)
Interface Description
Pin Function
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
Am79C940
23
CLSN
External Address Detection Interface
(EADI)
SF/BD
Collision (Input/Output)
An external indication that a collision condition has
been detected by the (internal or external) Medium
Attachment Unit (MAU), and that signals from two or
more nodes are present on the network. When the AUI
port is selected (PORTSEL [1–0] = 00), CLSN will be
activated when the CI± input pair is receiving a collision
indication from the external transceiver. CLSN will be
asserted high for the entire duration of the collision
detection, but will not be asserted during the SQE Test
message following a transmit message on the AUI.
When the 10BASE-T port is selected (PORTSEL [1–0]
= 01), CLSN will be asserted high when simultaneous
transmit and receive activity is detected (logically
detected when TXD±/TXP± and RXD± are both active).
When the DAI port is selected (PORTSEL [1–0] = 10),
CLSN will be asserted high when simultaneous transmit and receive activity is detected (logically detected
when RXCRS and TXEN are both active). When the
GPSI port is selected (PORTSEL [1–0] = 11), an input
from the external Manchester encoder/decoder signaling the MACE device that a collision condition has
been detected on the network, and any receive frame
in progress should be aborted.
Start Frame/Byte Delimiter (Output)
The external indication that a start of frame delimiter
has been received. The serial bit stream will follow on
the Serial Receive Data pin (SRD), commencing with
the destination address field. SF/BD will go high for 4
bit times (400 ns) after detecting the second 1 in the
SFD of a received frame. SF/BD will subsequently
toggle every 400 ns (1.25 MHz frequency) with the
rising edge indicating the start (first bit) in each
subsequent byte of the received serial bit stream.
SF/BD will be inactive during frame transmission.
SRD
Serial Receive Data (Output)
SRD is the decoded NRZ data from the network. It is
available for external address detection. Note that
when the 10BASE-T port is selected, transition on SRD
will only occur during receive activity. When the AUI or
DAI port is selected, transition on SRD will occur
dur ing both transmit and receive activity.
CLSN Configuration
SLEEP
PORTSEL
[1-0]
ENDPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
CLSN Output
1
01
1
10BASE-T
CLSN Output
1
10
1
DAI Port
CLSN Output
1
11
1
GPSI
CLSN Output
1
XX
0
Status Disabled
High Impedance (Note 2)
Interface Description
Pin Function
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
EAM/R
SRDCLK
External Address Match/Reject(Input)
Serial Receive Data Clock (Input/Output)
The incoming frame will be received dependent on the
receive operational mode of the MACE device, and the
polarity of the EAM/R pin. The EAM/R pin function is
programmed by use of the M/R bit in the Receive
Frame Control register. If the bit is set, the pin is configured as EAM. If the bit is reset, the pin is configured as
EAR. EAM/R can be asserted during packet reception
to accept or reject packets based on an external
address comparison.
The Serial Receive Data (SRD) output is synchronous
to SRDCLK running at the 10MHz receive data clock
frequency. The pin is configured as an input, only when
the GPSI port is selected. Note that when the
10BASE–T port is selected, transition on SRDCLK will
only occur during receive activity. When the AUI or DAI
port is selected, transition on SRDCLK will occur during
both transmit and receive activity.
24
Am79C940
SRD Configuration
SLEEP
PORTSEL
[1-0]
ENDPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
SRD Output
1
01
1
10BASE-T
SRD Output
1
10
1
DAI Port
SRD Output
1
11
1
GPSI
SRD Output
1
XX
0
Status Disabled
High Impedance
Interface Description
Pin Function
Note:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
SRDCLK Configuration
SLEEP
PORTSEL
[1-0]
ENDPLSIO
0
XX
X
Sleep Mode
High Impedance
1
00
1
AUI
SRDCLK Output
1
01
1
10BASE-T
SRDCLK Output
1
10
1
DAI Port
SRDCLK Output
1
11
1
GPSI
SRDCLK Output
1
XX
0
Status Disabled
High Impedance (Note 2)
Interface Description
Pin Function
Notes:
1. PORTSEL [1–0] and ENPLSIO are located in the PLS Configuration Control register (REG ADDR 14).
2. This pin should be externally terminated, if unused, to reduce power consumption.
Am79C940
25
HOST SYSTEM INTERFACE
DBUS15-0
DBUS contains read and write data to and from internal
registers and the Transmit and Receive FIFOs.
request transmit data transfer when 16, 32 or 64 bytes
are available in the Transmit FIFO, by programming the
Transmit FIFO Watermark (XMTFW bits) in the FIFO
Configuration Control register. TDTREQ will be
asserted only when Enable Transmit (ENXMT) is set in
the MAC Configuration Control register.
ADD4-0
FDS
Address Bus (Input)
FIFO Data Select (Input)
FIFO Data Select allows direct access to the transmit
or Receive FIFO without use of the ADD address bus.
FDS must be activated in conjunction with R/W. When
the MACE device samples R/W as high and FDS low,
a read cycle from the Receive FIFO will be initiated.
When the MACE chip samples R/W and FDS low, a
write cycle to the Transmit FIFO will be initiated. The
CS line should be inactive (high) when FIFO access is
requested using the FDS pin. If the MACE device samples both CS and FDS as active simultaneously, no
cycle will be executed, and DTV will remain inactive.
Data Bus (Input/Output/3-state)
ADD is used to access the internal registers and FIFOs
to be read or written.
R/W
Read/Write (Input)
Indicates the direction of data flow during the MACE
device register, Transmit FIFO, or Receive FIFO
accesses.
RDTREQ
Receive Data Transfer Request(Output)
Receive Data Transfer Request indicates that there is
data in the Receive FIFO to be read. When RDTREQ
is asserted there will be a minimum of 16 bytes to be
read except at the completion of the frame, in which
case EOF will be asserted. RDTREQ can be programmed to request receive data transfer when 16, 32
or 64 bytes are available in the Receive FIFO, by programming the Receive FIFO Watermark (RCVFW bits)
in the FIFO Configuration Control register. The first
assertion of RDTREQ will not occur until at least 64
bytes have been received, and the frame has been verified as non runt. Runt packets will normally be deleted
from the Receive FIFO with no external activity on
RDTREQ. When Runt Packet Accept is enabled (RPA
bit) in the User Test Register, RDTREQ will be asserted
when the runt packet completes, and the entire frame
resides in the Receive FIFO. RDTREQ will be asserted
only when Enable Receive (ENRCV) is set in the MAC
Configuration Control register.
The RCVFW can be overridden by enabling the Low
Latency Receive function (setting LLRCV bit) in the
Receive Frame Control register, which allows
RDTREQ to be asserted after only 12 bytes have been
received. Note that use of this function exposes the
system interface to premature termination of the
receive frame, due to network events such as collisions
or runt packets. It is the responsibility of the system
designer to provide adequate recovery mechanisms for
these conditions.
TDTREQ
Transmit Data Transfer Request (Output)
Transmit Data Transfer Request indicates there is
room in the Transmit FIFO for more data. TDTREQ is
asserted when there are a minimum of 16 empty bytes
in the Transmit FIFO. TDTREQ can be programmed to
26
DTV
Data Transfer Valid (Output/3-state)
When asserted, indicates that the read or write operation has completed successfully. The absence of DTV
at the termination of a host access cycle on the MACE
device indicates that the data transfer was unsuccessful. DTV need not be used if the system interface can
guarantee that the latency to TDTREQ and RDTREQ
assertion and de-assertion will not cause the Transmit
FIFO to be over-written or the Receive FIFO to be
over-read. In this case, the latching or strobing of read
or write data can be synchronized to the SCLK input
rather than to the DTV output.
EOF
End Of Frame (Input/Output/3-state)
End Of Frame will be asserted by the MACE device
when the last byte/word of frame data is read from the
Receive FIFO, indicating the completion of the frame
data field for the receive message. End Of Frame must
be asserted low to the MACE device when the last
byte/word of the frame is written into the Transmit
FIFO.
BE1–0
Byte Enable (Input)
Used to indicate the active portion of the data transfer
to or from the internal FIFOs. For word (16-bit) transfers, both BE0 and BE1 should be activated by the
external host/controller. Single byte transfers are performed by identifying the active data bus byte and activating only one of the two signals. The function of the
BE1-0 pins is programmed using the BSWP bit (BIU
Configuration Control register, bit 6). BE1-0 are not
required for accesses to MACE device registers.
Am79C940
CS
Chip Select (Input)
Used to access the MACE device FIFOs and internal
registers locations using the ADD address bus. The
FIFOs may alternatively be directly accessed without
supplying the FIFO address, by using the FDS and
R/W pins.
INTR
Interrupt (Output, Open Drain)
An attention signal indicating that one or more of the
following status flags are set: XMTINT, RCVINT,
MPCO, RPCO, RCVCCO, CERR, BABL, or JAB. Each
interrupt source can be individually masked. No interrupt condition can take place in the MACE device
immediately after a hardware or software reset.
RESET
Reset (Input)
Reset clears the internal logic. Reset can be asynchronous to SCLK, but must be asserted for a minimum
duration of 15 SCLK cycles.
IEEE 1149.1 TEST ACCESS PORT (TAP)
INTERFACE
TCK
Test Clock (Input)
The clock input for the boundary scan test mode operation. TCK can operate up to 10 MHz. TCK has an internal (not SLEEP disabled) pull up.
TMS
Test Mode Select (Input)
A serial input bit stream used to define the specific
boundary scan test to be executed. TMS has an internal (not SLEEP disabled) pull up.
TDI
Test Data Input (Input)
The test data input path to the MACE device. TDI has
an internal (not SLEEP disabled) pull up.
TDO
Test Data Out (Output)
SCLK
The test data output path from the MACE device.
System Clock (Input)
The system clock input controls the operational frequency of the slave interface to the MACE device and
the internal processing of frames. SCLK is unrelated to
the 20 MHz clock frequency required for the 802.3/
Ethernet interface. The SCLK frequency range is
1 MHz-25 MHz.
GENERAL INTERFACE
XTAL1
EDSEL
System Clock Edge Select (Input)
EDSEL is a static input that allows System Clock
(SCLK) edge selection. If EDSEL is tied high, the bus
interface unit will assume falling edge timing. If EDSEL
is tied low, the bus interface unit will assume rising
edge timing, which will effectively invert the SCLK as it
enters the MACE device, i.e., the address, control lines
(CS, R/W, FDS, etc) and data are all latched on the rising edge of SCLK, and data out is driven off the rising
edge of SCLK.
TC
Timing Control (Input)
The Timing Control input conditions the minimum number of System Clocks (SCLK) cycles taken to read or
write the internal registers and FIFOs. TC can be used
as a wait state generator, to allow additional time for
data to be presented by the host during a write cycle,
or allow additional time for the data to be latched during
a read cycle. TC has an internal (SLEEP disabled)
pull up.
Timing Control
TC
1
0
Number of
Clocks
2
3
Crystal Connection (Input)
The internal clock generator uses a 20 MHz crystal that
is attached to pins XTAL1 and XTAL2. Internally, the
20 MHz crystal frequency is divided by two which
determines the network data rate. Alternatively, an
external 20 MHz CMOS-compatible clock signal can be
used to drive this pin. The MACE device supports the
use of 50 pF crystals to generate a 20 MHz frequency
which is compatible with the IEEE 802.3 network
fre quency tolerance and jitter specifications.
XTAL2
Crystal Connection (Output)
The internal clock generator uses a 20 MHz crystal that
is attached to pins XTAL1 and XTAL2. If an external
clock generator is used on XTAL1, then XTAL2 should
be left unconnected.
SLEEP
Sleep Mode (Input)
The optimal power savings made is extracted by
asserting the SLEEP pin with both the Auto Wake
(AWAKE bit) and Remote Wake (RWAKE bit) functions
disabled. In this “deep sleep” mode, all outputs will be
forced into their inactive or high impedance state, and
all inputs will be ignored except for the SLEEP, RESET,
SCLK, TCK, TMS, and TDI pins. SCLK must run for 5
cycles after the assertion of SLEEP. During the “Deep
Sleep”, the SCLK input can be optionally suspended
for maximum power savings. Upon exiting “Deep
Sleep”, the hardware RESET pin must be asserted and
the SCLK restored. The system must delay the setting
Am79C940
27
of the bits in the MAC configuration Control Register of
the internal analog circuits by 1 ns to allow for
stabilization.
If the AWAKE bit is set prior to the activation of SLEEP,
the 10BASE–T receiver and the LNKST output pin
remain operational.
power and ground pins are not deleted. The MACE
device does have several sets of media interfaces
which typically go unused in most designs, however.
Pins from some of these interfaces are deleted instead.
Removed are the following:
■ TXDAT– (previously used for the DAI interface)
If the RWAKE bit is set prior to SLEEP being asserted,
the Manchester encoder/decoder, AUI and 10BASE-T
cells remain operational, as do the SRD, SRDCLK and
SF/BD outputs.
■ SRD (previously used for the EADI interface)
The input on XTAL1 must remain active for the AWAKE
or RWAKE features to operate. After exit from the Auto
Wake or Remote Wake modes, activation of hardware
RESET is not required when SLEEP is reasserted.
Note that pins from four separate interfaces are
removed rather than removing all the pins from a single
interface. Each of these pins comes from one of the
four sides of the device. This is done to maintain symmetry, thus avoiding bond out problems.
On deassertion of SLEEP, the MACE device will go
through an internally generated hardware reset
sequence, requiring re-initialization of MACE registers.
Power Supply
DVDD
■ RXPOL (previously used as a receive frame polarity
LED driver)
In general, the most critical of the four removed pins
are TXDAT– and SRD. Depending on the application,
either the DAI or the EADI interface may be important.
In most designs, however, this will not be the case.
PINS REMOVED FOR TQFP PACKAGE
AND THEIR EFFECTS
Digital Power
There are four Digital VDD pins.
TXDAT–
DVSS
Digital Ground
There are six Digital VSS pins.
AVDD
Analog Power
There are four analog VDD pins. Special attention
should be paid to the printed circuit board layout to
avoid excessive noise on the supply to the PLL in the
Manchester encoder/decoder (pins 66 and 83 in PLCC,
pins 67 and 88 in PQFP). These supply lines should be
kept separate from the DVDD lines as far back to the
power supply as is practically possible.
AVSS
Analog Ground
There are two analog VSS pins. Special attention
should be paid to the printed circuit board layout to
avoid excessive noise on the PLL supply in Manchester encoder/decoder (pin 73 in PLCC, pin 74 in PQFP).
These supply lines should be kept separate from the
DV SS lines as far back to the power supply as is
practically possible.
PIN FUNCTIONS NOT AVAILABLE WITH
THE 80-PIN TQFP PACKAGE
In the 84-pin PLCC configuration, ALL the pins are
used while in the 100-pin PQFP version, 16 pins are
specified as No Connects. Moving to the 80-pin TQFP
configuration requires the removal of 4 pins. Since
Ethernet controllers with integrated 10BASE-T have
analog portions which are very sensitive to noise,
28
■ DTV (previously used for the host interface)
The removal of TXDAT– means that the DAI interface is
no longer usable. The DAI interface was designed to be
used with media types that do not require DC isolation
between the MAU and the DTE. Media which do not require DC isolation can be implemented more simply
using the DAI interface, rather than the AUI interface. In
most designs this is not a problem because most media
requires DC isolation (10BASE-T, 10BASE2, 10BASE5)
and will use the AUI port. About the only media which
does not require DC isolation is 10BASE-F.
SRD
The SRD pin is an output pin used by the MACE device
to transfer a receive data stream to external address
detection logic. It is part of the EADI interface. This pin
is used to help interface the MACE device to an external CAM device. Use of an external CAM is typically
required when an application will operate in promiscuous mode and will need perfect filtering (i.e., the internal hash filter will not suffice). Example applications for
this sort of operation are bridges and routers. Lack of
perfect filtering in these applications forces the CPU to
be more involved in filtering and thus either slows the
forwarding rates achieved or forces the use of a more
powerful CPU.
DTV
The DTV pin is part of the host interface to the MACE
device. It is used to indicate that a read or write cycle
to the MACE device was successful. If DTV is not asserted at the end of a cycle, the data transfer was not
successful. Basically, this will happen on a write to a
full transmit FIFO or a read from an empty receive
Am79C940
FIFO. In general, there are ways to ensure that a
transfer is always valid; so this pin is not required in
many designs. For instance, the TDTREQ and
RDTREQ pins can be used to monitor the state of the
FIFOs to ensure that data transfer only occurs at the
correct times.
RXPOL
RXPOL is typically used to drive an LED indicating the
polarity of receive frames. This function is not
necessary for correct operation of the Ethernet and
serves strictly as a status indication to a user. The status of the receive polarity is still available through the
PHYCC register.
Am79C940
29
FUNCTIONAL DESCRIPTION
The Media Access Controller for Ethernet (MACE) chip
embodies the Media Access Control (MAC) and Physical Signaling (PLS) sub-layers of the 802.3 Standard.
The MACE device provides the IEEE defined Attachment Unit Interface (AUI) for coupling to remote Media
Attachment Units (MAUs) or on-board transceivers.
The MACE device also provides a Digital Attachment
I n t e r f a c e ( D A I ) , b y -p a s s i n g t h e d i f f e r e n t i a l
AUI interface.
The system interface provides a fundamental data
conduit to and from an 802.3 network. The MACE device in conjunction with a user defined DMA engine,
provides an 802.3 interface tailored to a specific
application.
In addition, the MACE device can be combined with
similarly architected peripheral devices and a
multi-channel DMA controller, thereby providing the
system with access to multiple peripheral devices with
a single master interface to memory.
Network Interfaces
The MACE device can be connected to an 802.3 network using any one of the AUI, 10 BASE-T, DAI and
GPSI network interfaces. The Attachment Unit Interface (AUI) provides an IEEE compliant differential interface to a remote MAU or an on-board transceiver.
An integrated 10BASE-T MAU provides a direct interface for twisted pair Ethernet networks. The DAI port
can connect to local transceiver devices for 10BASE2,
10BASE-T or 10BASE-F connections. A General Purpose Serial Interface (GPSI) is supported, which effectively bypasses the integrated Manchester encoder/
decoder, and allows direct access to/from the integral
802.3 Media Access Controller (MAC) to provide support for external encoding/decoding schemes. The interface in use is determined by the PORTSEL [1-0] bits
in the PLS Configuration Control register.
The EADI port does not provide network connectivity,
but allows an optional external circuit to assist in
receive packet accept/reject.
System Interface
The MACE device is a slave register based peripheral.
All transfers to and from the device, including data, are
performed using simple memory or I/O read and write
commands. Access to all registers, including the Transmit and Receive FIFOs, are performed with identical
read or write timing. All information on the system interface is synchronous to the system clock (SCLK), which
allows simple external logic to be designed to
interrogate the device status and control the network
data flow.
The Receive and Transmit FIFOs can be read or written by driving the appropriate address lines and assert-
30
ing CS and R/W. A n alter nati ve FIFO ac cess
mechanism allows the use of the FDS and the R/W
lines, ignoring the address lines (ADD4-0). The state of
the R/W line in conjunction with the FDS input determines whether the Receive FIFO is read (R/W high) or
the Transmit FIFO written (R/W low). The MACE device system interface permits interleaved transmit and
receive bus transfers, allowing the Transmit FIFO to be
filled (primed) while a frame is being received from the
network and/or read from the Receive FIFO.
In receive operation, the MACE device asserts Receive
Data Transfer Request (RDTREQ) when the FIFO contains adequate data. For the first indication of a new
receive frame, 64 bytes must be received, assuming
normal operation. Once the initial 64 byte threshold has
been reached, RDTREQ assertion and de-assertion is
dependent on the programming of the Receive FIFO
Watermark (RCVFW bits in the BIU Configuration Control register). The RDTREQ can be programmed to
activate when there are 16, 32 or 64 bytes of data available in the Receive FIFO. Enable Receive (ENRCV bit
in MAC Configuration Control register) must be set to
assert RDTREQ. If the Runt Packet Accept feature is
invoked (RPA bit in User Test Register), RDTREQ will
be asserted for receive frames of less than 64 bytes on
the basis of internal and/or external address match
only. When RPA is set, RDTREQ will be asserted when
the entire frame has been received or when the initial
64 byte threshold has been exceeded. See the FIFO
Sub-Systems section for further details.
Note that the Receive FIFO may not contain 64 data
bytes at the time RDTREQ is asserted, if the automatic
pad stripping feature has been enabled (ASTRP RCV
bit in the Receive Frame Control register) and a minimum length packet with pad is received. The MACE
device will check for the minimum received length from
the network, strip the pad characters, and pass only the
data frame through the Receive FIFO.
If the Low Latency Receive feature is enabled (LLRCV
bit set in Receive Frame Control Register), RDTREQ
will be asserted once a low watermark threshold has
been reached (12 bytes plus some additional synchronization time). Note that the system interface will therefore be exposed to potential disruption of the receive
frame due to a network condition (see the FIFO
Sub-System description for additional details).
In transmit operation, the MACE device asserts Transmit Data Transfer Request (TDTREQ) dependent on
the programming of the Transmit FIFO Watermark
(XMTFW bits in the BIU Configuration Control register).
TDTREQ will be permanently asserted when the
Transmit FIFO is empty. The TDTREQ can be programmed to activate when there are 16, 32 or 64 bytes
of space available in the Transmit FIFO. Enable Transmit (ENXMT bit in MAC Configuration Control register)
must be set to assert TDTREQ. Write cycles to the
Am79C940
Transmit FIFO will not return DTV if ENXMT is disabled, and no data will be written. The MACE device
will commence the preamble sequence once the
Transmit Start Point (XMTSP bits in BIU Configuration
Control register) threshold is reached in the Transmit
FIFO.
The Transmit FIFO data will not be overwritten until at
least 512 data bits have been transmitted onto the network. If a collision occurs within the slot time (512 bit
time) window, the MACE device will generate a jam sequence (a 32-bit all zeroes pattern) before ceasing the
transmission. The Transmit FIFO will be reset to point
at the start of the transmit data field, and the message
will be retried after the random back-off interval has
expired.
DETAILED FUNCTIONS
Block Level Description
The following sections describe the major sub-blocks
of and the external interfaces to the MACE device.
Bus Interface Unit (BIU)
The BIU performs the interface between the host or
system bus and the Transmit and Receive FIFOs, as
well as all chip control and status registers. The BIU
can be configured to accept data presented in either little-endian or big indian format, minimizing the external
logic required to access the MACE device internal
FIFOs and registers. In addition, the BIU directly
supports 8-bit transfers and incorporates features to
simplify interfacing to 32-bit systems using
external latches.
Externally, the FIFOs appear as two independent registers located at individual addresses. The remainder
of the internal registers occupy 30 additional consecutive addresses, and appear as 8-bits wide.
BIU to FIFO Data Path
The BIU operates assuming that the 16-bit data path
to/from the internal FIFOs is configured as two independent byte paths, activated by the Byte Enable
sig nals BE0 and BE1.
BE0 and BE1 are only used during accesses to the
16-bit wide Transmit and Receive FIFOs. After hardware or software reset, the BSWP bit will be cleared.
FIFO accesses to the MACE device will operate
assuming an Intel 80x86 type memory convention
(most significant byte of a word stored in the higher
addressed byte). Word data transfers to/from the
FIFOs over the DBUS15-0 lines will have the least significant byte located on DBUS7-0 (activated by BE0)
and the most significant byte located on DBUS15-8
(activated by BE1).
FIFO data can be read or written using either byte and/
or word operations.
If byte operation is required, read/write transfers can be
performed on either the upper or lower data bus by
asserting the appropriate byte enable. For instance
with BSWP = 0, reading from or writing to DBUS15-8 is
accomplished by asserting BE1, and allows the data
stream to be read from or written to the appropriate
FIFO in byte order (byte 0, byte 1,....byte n). It is equally
valid to read or write the data stream using DBUS7–0
and by asserting BE0. For BSWP = 1, reading from or
writing to DBUS15-8 is accomplished by asserting BE0,
and allows the byte stream to be transferred in byte
order.
When word operations are required, BSWP ensures
that the byte ordering of the target memory is compatible with the 802.3 requirement to send/receive the data
stream in byte ascending order. With BSWP = 0, the
data transferred to/from the FIFO assumes that byte n
will be on DBUS7-0 (activated by BE0) and byte n+1
will be on DBUS15-8 (activated by BE1). With BSWP =
1, the data transferred to/from the FIFO assumes that
byte n will be presented on DBUS15-8 (activated by
BE0), and byte n+1 will be on DBUS7-0 (activated by
BE1).
There are some additional special cases to the above
generalized rules, which are as follows:
(a) When performing byte read operations, both
halves of the data bus are driven with identical
data, effectively allowing the user to arbitrarily read
from either the upper or lower data bus, when only
one of the byte enables is activated.
(b) When byte write operations are performed, the
Transmit FIFO latency is affected. See the FIFO
Sub-System section for additional details.
(c) If a word read is performed on the last data byte of
a receive frame (EOF is asserted), and the message contained an odd number of bytes but the
host requested a word operation by asserting both
BE0 and BE1, then the MACE device will present
one valid and one non-valid byte on the data bus.
The placement of valid data for the data byte is dependent on the target memory architecture. Regardless of BSWP, the single valid byte will be read
from the BE0 memory bank. If BSWP = 0, BE0 corresponds to DBUS7-0; if BSWP = 1, BE0 corresponds to DBUS15-8.
(d) If a byte read is performed when the last data byte
is read for a receive frame (when the MACE device
activates the EOF signal), then the same byte will
be presented on both the upper and lower byte of
the data bus, regardless of which byte enable was
activated (as is the case for all byte read operations).
(e) When writing the last byte in a transmit message
to the Transmit FIFO, the portion of the data bus
Am79C940
31
that the last byte is transferred over is irrelevant,
providing the appropriate byte enable is used. For
BSWP = 0, data can be presented on DBUS7-0
using BE0 or DBUS15-8 using BE1. For BSWP =
1, data can be presented on DBUS7-0 using BE1
or DBUS15-8 using BE0.
Byte Alignment For Register Write Operations
BE0
BE1
BSWP
DBUS7-0
X
X
0
Write
Data
X
(f) When neither BE0 nor BE1 are asserted, no data
transfer will take place. DTV will not be asserted.
BE1
BSWP
DBUS7-0
DBUS15-8
0
0
0
n
n+1
0
1
0
n
n
1
0
0
n
n
1
1
0
X
X
0
0
1
n+1
n
0
1
1
n
n
1
0
1
n
n
1
1
1
X
X
1
X
X
Write
Data
FIFO Subsystem
Byte Alignment For FIFO Read Operations
BE0
X
DBUS15-8
The MACE device has two independent FIFOs, with
128-bytes for receive and 136-bytes for transmit operations. The FIFO sub-system contains both the FIFOs,
and the control logic to handle normal and exception
related conditions.
The Transmit and Receive FIFOs interface on the network side with the serializer/de-serializer in the MAC
engine. The BIU provides access between the FIFOs
and the host system to enable the movement of data to
and from the network.
Internally, the FIFOs appear to the BIU as independent
16-bit wide registers. Bytes or words can be written to
the Transmit FIFO (XMTFIFO), or read from the
Receive FIFO (RCVFIFO). Byte and word transfers
can be mixed in any order. The BIU will ensure correct
byte ordering dependent on the target host system, as
determined by the programming of the BSWP bit in the
BIU Configuration Control register.
Byte Alignment For FIFO Write Operations
BE0
BE1
BSWP
DBUS7-0
DBUS15-8
0
0
0
n
n+1
0
1
0
n
X
1
0
0
X
n
1
1
0
X
X
0
0
1
n+1
n
0
1
1
X
n
1
0
1
n
X
The XMTFIFO and RCVFIFO have three different
modes of operation. These are Normal (Default), Burst
and Low Latency Receive. Default operation will be
used after the hardware RESET pin or software
SWRST bit have been activated. The remainder of this
general description applies to all modes except where
specific differences are noted.
1
1
1
X
X
Transmit FIFO—General Operation
BIU to Control and Status
Register Data Path
All registers in the address range 2-31 are 8-bits wide.
When a read cycle is executed on any of these registers, the MACE device will drive data on both bytes of
the data bus, regardless of the programming of BSWP.
When a write cycle is executed, the MACE device
strobes in data based on the programming of BSWP as
shown in the tables below. All accesses to addresses
2-31 are independent of the BE0 and BE1 pins.
Byte Alignment For Register Read Operations
BE0
X
BE1
X
BSWP
0
DBUS7-0
Read
DBUS15-8
Read
X
X
1
Data
Read
Data
Read
Data
Data
32
When writing bytes to the XMTFIFO, certain restrictions apply. These restrictions have a direct influence
on the latency provided by the FIFO to the host system.
When a byte is written to the FIFO location, the entire
word location is used. The unused byte is marked as a
hole in the XMTFIFO. These holes are skipped during
the serialization process performed by the MAC
engine, when the bytes are unloaded from the
XMTFIFO.
For instance, assume the Transmit FIFO Watermark
(XMTFW) is set for 32 write cycles. If the host writes
byte wide data to the XMTFIFO, after 36 write cycles
there will be space left in the XMTFIFO for only 32
more write cycles. Therefore TDTREQ will de-assert
even though only 36-bytes of data have been loaded
into the XMTFIFO. Transmission will not commence
until 64-bytes or the End-of-Frame are available in the
XMFIFO, so transmission would not start, and
Am79C940
TDTREQ would remain de-asserted. Hence for byte
wide data transfers, the XMTFW should be programmed to the 8 or 16 write cycle limit, or the host
should ensure that sufficient data will be written to the
XMTFIFO after TDTREQ has been de-asserted (which
is permitted), to guarantee that the transmission will
commence. A third alternative is to program the Transmit Start Point (XMTSP) in the BIU Configuration Control register to below the 64-byte default; thereby
imposing a lower latency to the host system requiring
additional data to ensure the XMTFIFO does not
underflow during the transmit process, versus using
the default XMTSP value. Note that if 64 single byte
writes are executed on the XMTFIFO, and the XMTSP
is set to 64-bytes, the transmission will commence, and
all 64-bytes of information will be accepted by
the XMTFIFO.
The number of write cycles that the host uses to write
the packet into the Transmit FIFO will also directly influence the amount of space utilized by the transmit
message. If the number of write cycles (n) required to
transfer a packet to the Transmit FIFO is even, the
number of bytes used in the Transmit FIFO will be 2*n.
If the number of write cycles required to transfer a
packet to the Transmit FIFO is odd, the number of
bytes used in the Transmit FIFO will be 2*n + 2 because the End Of Frame indication in the XMTFIFO is
always placed at the end of a 4-byte boundary. For example, a 32-byte message written as bytes (n = 32 cycles) will use 64-bytes of space in the Transmit FIFO
(2*n = 64), whereas a 65-byte message written as 32
words and 1 byte (n = 33 cycles) would use 68-bytes
(2*n + 2 = 68) .
The Transmit FIFO has been sized appropriately to
minimize the system interface overhead. However,
consideration must be given to overall system design if
byte writes are supported. In order to guarantee that
sufficient space is present in the XMTFIFO to accept
the number of write cycles programmed by the XMTFW
(including an End Of Frame delimiter), TDTREQ may
go inactive before the XMTSP threshold is reached
when using the non burst mode (XMTBRST = 0). For
instance, assume that the XMTFW is programmed to
allow 32 write cycles (default), and XMTSP is programmed to require 64 bytes (default) before starting
transmission. Assuming that the host bursts the transmit data in a 32 cycle block, writing a single byte anywhere within this block will mean that XMTSP will not
have been reached. This would be a typical scenario if
the transmit data buffer was not aligned to a word
boundary. The MACE device will continue to assert
TDTREQ since an additional 36 write cycles can still be
executed. If the host starts a second burst, the XMTSP
will be reached, and TDTREQ will deassert when less
that 32 write cycle can be performed although the data
written by the host will continue to be accepted.
The host must be aware that additional space exists in
the XMTFIFO although TDTREQ becomes inactive,
and must continue to write data to ensure the XMTSP
threshold is achieved. No transmit activity will commence until the XMTSP threshold is reached.
Once 36 write cycles have been executed.
Note that write cycles can be performed to the XMTFIFO even if the TDTREQ is inactive. When TDTREQ
is asserted, it guarantees that a minimum amount of
space exists, when TDTREQ is deasserted, it does not
necessarily indicate that there is no space in the XMTFIFO. The DTV pin will indicate the successful acceptance of data by the Transmit FIFO.
As another example, assume again that the XMTFW is
programmed for 32 write cycles. If the host writes word
wide data continuously to the XMTFIFO, the TDTREQ
will deassert when 36 writes have executed on the
XMTFIFO, at which point 72-bytes will have been written to the XMTFIFO, the 64-byte XMTSP will have
been exceeded and the transmission of preamble will
have commenced. TDTREQ will not re-assert until the
transmission of the packet data has commenced and
the possibility of losing data due to a collision within the
slot time is removed (512 bits have been transmitted
without a collision indication). Assuming that the host
actually stopped writing data after the initial 72-bytes,
there will be only 16-bytes of data remaining in the
XMTFIFO (8-bytes of preamble/SFD plus 56-bytes of
data have been transmitted), corresponding to 12.8 µs
of latency before an XMTFIFO underrun occurs. This
latency is considerably less than the maximum possible 57.6 µs the system may have assumed. If the host
had continued with the block transfer until 64 write
cycles had been performed, 128-bytes would have
been written to the XMTFIFO, and 72-bytes of latency
would remain (57.6 µ s) when TDTREQ was re-asserted.
Transmit FIFO—Burst Operation
The XMTFIFO burst mode, programmed by the XMTBRST bit in the FIFO Configuration Control register,
modifies TDTREQ behavior. The assertion of TDTREQ
is controlled by the programming of the XMTFW bits,
such that when the specified number of write cycles
can be guaranteed (8, 16 or 32), TDTREQ will be asserted. TDTREQ will be de-asserted when the
XMT FIFO can only accept a single write cycle (one
word write including an End Of Frame delimiter) allowing the external device to burst data into the XMTFIFO
when TDTREQ is asserted, and stop when TDTREQ
is deasserted.
Receive FIFO—General Operation
The Receive FIFO contains additional logic to ensure
that sufficient data is present in the RCVFIFO to allow
the specified number of bytes to be read, regardless of
the ordering of byte/word read accesses. This has an
Am79C940
33
impact on the perceived latency that the Receive FIFO
provides to the host system. The description and table
below outline the point at which RDTREQ will be
asserted when the first duration of the packet has been
received and when any subsequent transfer of the
packet to the host system is required.
No preamble/SFD bytes are loaded into the Receive
FIFO. All references to bytes pass through the receive
FIFO. These references are received after the preamble/SFD sequence.
The first assertion of RDTREQ for a packet will occur
after the longer of the following two conditions is met:
■ 64-bytes have been received (to assure runt packets and packets experiencing collision within the
slot time will be rejected).
■ The RCVFW threshold is reached plus an additional
12 bytes. The additional 12 bytes are necessary to
ensure that any permutation of byte/word read
access is guaranteed. They are required for all
threshold values, but in the case of the 16 and
32-byte thresholds, the requirement that the slot time
criteria is met dominates. Any subsequent assertion
of RDTREQ necessary to complete the transfer of
the packet will occur after the RCVFW threshold is
reached plus an additional 12 bytes. The table below
also outlines the latency provided by the MACE device when the RDTREQ is asserted.
Receive FIFO Watermarks, RDTREQ Assertion and Latency
RCVFW
[1-0]
Bytes Required for
First Assertion of
RDTREQ
Bytes of Latency
After First Assertion
of RDTREQ
Bytes Required for
Subsequent Assertion
of RDTREQ
Bytes of Latency After
Subsequent Assertion
of RDTREQ
00
64
64
28
100
01
64
64
44
84
10
76
52
76
52
11
XX
XX
XX
XX
Receive FIFO—Burst Operation
The RCVFIFO also provides a burst mode capability,
programmed by the RCVBRST bit in the FIFO Configuration Control register, to modify the operation of
RDTREQ.The assertion of RDTREQ will occur according to the programming of the RCVFW bits. RDTREQ
will be de-asserted when the RCVFIFO can only provide a single read cycle (one word read). This allows
the external device to burst data from the RCVFIFO
once RDTREQ is asserted, and stop when RDTREQ
is deasserted.
Receive FIFO—Low Latency Receive Operation
The LOW Latency Receive mode can be programmed
using the Low Latency Receive bit (LLRCV in the
Receive Frame Control register). This effectively
causes the assertion of RDTREQ to be directly coupled
to the low watermark of 12 bytes in the RCVFIFO.
Once the 12-byte threshold is reached (plus some
internal synchronization delay of less than 1 byte),
RDTREQ will be asserted, and will remain active until
the RCVFIFO can support only one read cycle
(one wor d of data), as in the bur st oper ati on
described earlier. The exception is the case where 4-8
bytes of padding is required by the FIFO design, unless
it is the end of the packet.
The intended use for the Low Latency Receive mode is
to allow fast forwarding of a received packet in a bridge
application. In this case, the receiving process is made
aware of the receive packet after only 9.6 µs, instead of
waiting up to 60.8 µs (76-bytes) necessary for the initial
34
assertion of RDTREQ. An Ethernet-to-Ethernet bridge
employing the MACE device (on all the Ethernet
connections) with the XMTSP of all MACE controller
XMT FIFOs set to the minimum (4-bytes), forwarding of
a receive packet can be achieved within a sub 20 µs
delay including processing overhead.
Note, however, that this mode places significant burden on the host processor. The receiving MACE device
will no longer delete runt packets. A runt packet will
have the Receive Frame Status appended to the receive data which the host must read as normal. The
MACE device will not attempt to delete runt packets
from the RCVFIFO in the Low Latency Receive mode.
Collision fragments will also be passed to the host if
they are detected after the 12-byte threshold has been
reached. If a collision occurs, the Receive Frame Status (RCVFS) will be appended to the data successfully
received in the RCVFIFO up to the point the collision
was detected. No additional receive data will be written
to the RCVFIFO. Note that the RCVFS will not become
available until after the receive activity ceases. The collision indication (CLSN) in the Receive Status
(RCVSTS) will be set, and the Receive Message Byte
Count (RCVCNT) will be the correct count of the total
duration of activity, including the period that collision
was detected. The detection of normal (slot time) collisions versus late collisions can only be made by
counting the number of bytes that were successfully received prior to the termination of the packet data.
In all cases where the reception ends prematurely (runt
or collision), the data that was successfully received
Am79C940
prior to the termination of reception must be read from
the RCVFIFO before the RCVFS bytes are available.
of packet data) messages to be transmitted
and/or received.
Media Access Control (MAC)
Framing (Frame Boundary Delimitation,
Frame Synchronization)
The Media Access Control engine is the heart of the
MACE device, incorporating the essential protocol
requirements for operation of a compliant Ethernet/
802.3 node, and providing the interface between the
FIFO sub-system and the Manchester Encoder/
Decoder (MENDEC).
The MAC engine is fully compliant to Section 4 of ISO/
IEC 8802-3 (ANSI/IEEE Standard 1990 Second edition) and ANSI/IEEE 802.3 (1985).
The MAC engine provides enhanced features, programmed through the Transmit Frame Control and
Receive Frame Control registers, designed to minimize
host supervision and pre or post message processing.
These features include the ability to disable retries after
a collision, dynamic FCS generation on a
packet-by-packet basis, and automatic pad field
insertion and deletion to enforce minimum frame
size attributes.
The two primary attributes of the MAC engine are:
■ Transmit and receive message data encapsulation
— Framing (frame boundary delimitation, frame
synchronization)
— Addressing (source and destination address
handling)
— Error detection (physical medium transmission
errors)
■ Media access management
— Medium allocation (collision avoidance)
— Contention resolution (collision handling)
Transmit and Receive Message Data
Encapsulation
Data passed to the MACE device Transmit FIFO will be
assumed to be correctly formatted for transmission
over the network as a valid packet. The user is required
to pass the data stream for transmission to the MACE
chip in the correct order, according to the byte ordering
convention programmed for the BIU.
The MACE device provides minimum frame size
enforcement for transmit and receive packets. When
APAD XMT = 1 (default), transmit messages will be
padded with sufficient bytes (containing 00h) to ensure
that the receiving station will observe an information
field (destination address, source address, length/type,
data and FCS) of 64-bytes. When ASTRP RCV = 1
(default), the receiver will automatically strip pad and
FCS bytes from the received message if the value in
the length field is below the minimum data size
(46-bytes). Both features can be independently
over-ridden to allow illegally short (less than 64-bytes
The MACE device will autonomously handle the construction of the transmit frame. When the Transmit
FIFO has been filled to the predetermined threshold
(set by XMTSP), and providing access to the channel
is currently permitted, the MACE device will commence
the 7 byte preamble sequence (10101010b, where first
bit transmitted is a 1). The MACE device will subsequently append the Start Frame Delimiter (SFD) byte
(10101011) followed by the serialized data from the
Transmit FIFO. Once the data has been completed, the
MACE device will append the FCS (most significant bit
first) computed on the entire data portion of the
message.
Note that the user is responsible for the correct ordering and content in each of the fields in the frame,
including the destination address, source address,
length/type and packet data.
The receive section of the MACE device will detect an
incoming preamble sequence and lock to the encoded
clock. The internal MENDEC will decode the serial bit
stream and present this to the MAC engine. The MAC
will discard the first 8-bits of information before searching for the SFD sequence. Once the SFD is detected,
all subsequent bits are treated as part of the frame. The
MACE device will inspect the length field to ensure
minimum frame size, strip unnecessary pad characters
(if enabled), and pass the remaining bytes through the
Receive FIFO to the host. If pad stripping is performed,
the MACE device will also strip the received FCS
bytes, although the normal FCS computation and
checking will occur. Note that apart from pad stripping,
the frame will be passed unmodified to the host. If the
length field has a value of 46 or greater, the MACE device will not attempt to validate the length against the
number of bytes contained in the message.
If the frame terminates or suffers a collision before
64-bytes of information (after SFD) have been
received, the MACE device will automatically delete
the frame from the Receive FIFO, without host intervention. Note however, that if the Low Latency Receive
option has been enabled (LLRCV = 1 in the Receive
Frame Control register), the MACE device will not
delete receive frames which experience a collision
once the 12-byte low watermark has been reached
(see the FIFO Sub-System section for additional
details).
Addressing (Source and Destination
Address Handling)
The first 6-bytes of information after SFD will be interpreted as the destination address field. The MACE
device provides facilities for physical, logical and
Am79C940
35
broadcast address reception. In addition, multiple
physical addresses can be constructed (perfect
address filtering) using external logic in conjunction
with the EADI interface.
Error Detection (Physical Medium
Transmission Errors)
The MACE device provides several facilities which
report and recover from errors on the medium. In addition, the network is protected from gross errors due to
inability of the host to keep pace with the MACE
device activity.
On completion of transmission, the MACE device will
report the Transmit Frame Status for the frame. The
exact number of transmission retry attempts is reported
(ONE, MORE used with XMTRC, or RTRY), and
whether the MACE device had to Defer (DEFER) due
to channel activity. In addition, Loss of Carrier is
reported, indicating that there was an interruption in the
ability of the MACE device to monitor its own transmission. Repeated LCAR errors indicate a potentially
faulty transceiver or network connection. Excessive
Defer (EXDEF) will be reported in the Transmit Retry
Count register if the transmit frame had to wait for an
abnormally long period before transmission.
Additional transmit error conditions are reported
through the Interrupt Register.
The Late Collision (LCOL) error indicates that the
transmission suffered a collision after the slot time.
This is indicative of a badly configured network. Late
collisions should not occur in normal operating network.
The Collision Error (CERR) indicates that the transceiver did not respond with an SQE Test message
within the predetermined time after a transmission
completed. This may be due to a failed transceiver,
disconnected or faulty transceiver drop cable, or the
fact the transceiver does not support this feature (or it
is disabled).
In addition to the reporting of network errors, the MACE
device will also attempt to prevent the creation of any
network error caused by inability of the host to service
the MACE device. During transmission, if the host fails
to keep the Transmit FIFO filled sufficiently, causing an
underflow, the MACE device will guarantee the
message is either sent as a runt packet (which will be
deleted by the receiving station) or has an invalid FCS
(which will also allow the receiving station to reject the
message).
The status of each receive message is passed via the
Receive Frame Status bytes. FCS and Framing errors
(FRAM) are reported, although the received frame is
still passed to the host. The FRAM error will only be
reported if an FCS error is detected and there are a non
integral number of bytes in the message. The MACE
36
device will ignore up to seven additional bits at the end
of a message (dribbling bits), which can occur under
normal network operating conditions. The reception of
eight additional bits will cause the MACE device to
de-serialize the entire byte, and will result in the
received message and FCS being modified.
Received messages which suffer a collision after
64-byte times (after SFD) will be marked to indicate
they have suffered a late collision (CLSN). Additional
counters are provided to report the Receive Collision
Count and Runt Packet Count to be used for network
statistics and utilization calculations.
Note that if the MACE device detects a received packet
which has a 00b pattern in the preamble (after the first
8-bits which are ignored), the entire packet will be
ignored. The MACE device will wait for the network to
go inactive before attempting to receive additional
frames.
Media Access Management
The basic requirement for all stations on the network
is to provide fairness of channel allocation. The 802.3/
Ethernet protocols define a media access mechanism
which permits all stations to access the channel with
equality. Any node can attempt to contend for the channel by waiting for a predetermined time (Inter Packet
Gap interval) after the last activity, before transmitting
on the media. The channel is a bus or multidrop communications medium (with various topological configurations permitted) which allows a single station to
transmit and all other stations to receive. If two nodes
simultaneously contend for the channel, their signals
will interact causing loss of data, defined as a collision.
It is the responsibility of the MAC to attempt to avoid
and recover from a collision, to guarantee data integrity
for the end-to-end transmission to the receiving station.
Medium Allocation (Collision Avoidance)
The IEEE 802.3 Standard (ISO/IEC 8802-3 1990)
requires that the CSMA/CD MAC monitors the medium
for traffic by watching for carrier activity. When carrier
is detected, the media is considered busy, and the
MAC should defer to the existing message.
The IEEE 802.3 Standard also allows optional two part
deferral after a receive message.
See ANSI/IEEE Std 802.3-1990 Edition, 4.2.3.2.1:
Note: “ It is possible for the PLS carrier sense indication to fail to be asserted during a collision on the
media. If the deference process simply times the interFrame gap based on this indication it is possible for a
short interFrame gap to be generated, leading to a
potential reception failure of a subsequent frame. To
enhance system robustness the following optional
measures, as specified in 4.2.8, are recommended
when interFrameSpacing Part1 is other than zero:”
Am79C940
(1) Upon completing a transmission, start timing the
interpacket gap, as soon as transmitting and carrier
Sense are both false.
See ANS t42I/IEEE Std 802.3-1990 Edition,
7.2.4.6 (1)):
“At the conclusion of the output function, the DTE
opens a time window during which it expects to see
the signal_quality_error signal asserted on the
Control In circuit. The time window begins when the
CARRIER_STATUS becomes CARRIER_OFF. If
execution of the output function does not cause
CARRIER_ON to occur, no SQE test occurs in the
DTE. The duration of the window shall be at least
4.0 µs but no more than 8.0 µs. During the time window the Carrier Sense Function is inhibited.”
(2) When timing an interFrame gap following
r ece pti on, re se t the i nte r Fr am e ga p ti mi ng i f
carrierSense becomes true during the first 2/3 of the
interFrame gap timing interval. During the final 1/3 of
the interval the timer shall not be reset to ensure fair
access to the medium. An initial period shorter than 2/
3 of the interval is permissible including zero.“
The MAC engine implements the optional receive two
part deferral algorithm, with a first part inter-frame-spacing time of 6.0 µs. The second part of
the inter-frame-spacing interval is therefore 3.6 µs.
The MACE device will perform the two part deferral
algorithm as specified in Section 4.2.8 (Process Deference). The Inter Packet Gap (IPG) timer will start timing
the 9.6 µs InterFrameSpacing after the receive carrier
i s d e -a s s e r t e d . D u r i n g t h e f i r s t p a r t d e f e r r a l
(InterFrameSpacingPart1-IFS1) the MACE device will
defer any pending transmit frame and respond to the
receive message. The IPG counter will be reset to zero
continuously until the carrier deasserts, at which point
the IPG counter will resume the 9.6 µs count once
again. Once the IFS1 period of 6.0µs has elapsed, the
MACE device will begin timing the second part deferral
(InterFrameSpacingPart2-IFS2) of 3.6 µs. Once IFS1
has completed, and IFS2 has commenced, the MACE
chip will not defer to a receive packet if a transmit
packet is pending. This means that the MACE device
will not attempt to receive an incoming packet, and it
will start to transmit at 9.6 µs regardless of network
activity, forcing a collision if an existing transmission is
in progress. The MACE device will guarantee to complete the preamble (64-bit) and jam (32-bit) sequence
before ceasing transmission and invoking the random
backoff algorithm.
In addition to the deferral after receive process, the
MACE device also allows transmit two part deferral to
be implemented as an option. The option can be disabled using the DXMT2PD bit in the MAC Configurati o n C o nt r o l r e g i s t er. Two p a r t d e fe r r a l a f te r
transmission is useful for ensuring that severe IPG
shrinkage cannot occur in specific circumstances,
causing a transmit message to follow a receive message so closely, as to make them indistinguishable.
During the time period immediately after a transmission
has been completed, the external transceiver (in the
case of a standard AUI connected device), should generate the SQE Test message (a nominal 10 MHz burst
of 5-15 BT duration) on the CI± pair (within 0.6-1.6 µs
after the transmission ceases). During the time period
in which the SQE Test message is expected the MACE
device will not respond to receive carrier sense.
The MACE device implements a carrier sense blinding
period within 0 µs-4.0 µs from deassertion of carrier
sense after transmission. This effectively means that
when transmit two part deferral is enabled (DXMT2PD
in the MAC Configuration Control register is cleared)
the IFS1 time is from 4 µs to 6 µs after a transmission.
However, since IPG shrinkage below 4 µs will not be
encountered on correctly configured networks, and
since the fragment size will be larger than the 4 µs
blinding window, then the IPG counter will be reset by
a worst case IPG shrinkage/fragment scenario and the
MACE device will defer its transmission. The MACE
chip will not restart the carrier sense blinding period if
carrier is detected within the 4.0-6.0 µs portion of IFS1,
but will restart timing of the entire IFS1 period.
Contention Resolution (Collision Handling)
Collision detection is performed and reported to the
MAC engine either by the integrated Manchester
Encoder/Decoder (MENDEC), or by use of an external
function (e.g. Serial Interface Adaptor, Am7992B)
utilizing the GPSI.
If a collision is detected before the complete preamble/
SFD sequence has been transmitted, the MACE device will complete the preamble/SFD before appending
the jam sequence. If a collision is detected after the
preamble/SFD has been completed, but prior to 512
bits being transmitted, the MACE device will abort the
transmission, and append the jam sequence immediately. The jam sequence is a 32-bit all zeroes pattern.
The MACE device will attempt to transmit a frame a
total of 16 times (initial attempt plus 15 retries) due to
normal collisions (those within the slot time). Detection
of collision will cause the transmission to be re-scheduled, dependent on the backoff time that the MACE device computes. Each collision which occurs during the
transmission process will cause the value of XMTRC in
the Transmit Retry Count register to be updated. If a
single retry was required, the ONE bit will be set in the
Transmit Frame Status. If more than one retry was required, the MORE bit will be set, and the exact number
of attempts can be determined (XMTRC+1). If all 16 attempts experienced collisions, the RTRY bit will be set
Am79C940
37
(ONE and MORE will be clear), and the transmit message will be flushed from the XMTFIFO, either by resetting the XMTFIFO (if no End-of-Frame tag exists) or by
moving the XMTFIFO read pointer to the next free location (If an End-of-Frame tag is present). If retries
have been disabled by setting the DRTRY bit, the
MACE device will abandon transmission of the frame
on detection of the first collision. In this case, only the
RTRY bit will be set and the transmit message will be
flushed from the XMTFIFO. The RTRY condition will
cause the de-assertion of TDTREQ, and the assertion
of the INTR pin, providing the XMTINTM bit is cleared.
nel activity is reduced, the nodes resolving the collision
time-out their slot time counters as normal.
If a collision is detected after 512 bit times have been
transmitted, the collision is termed a late collision. The
MACE device will abort the transmission, append the
jam sequence and set the LCOL bit in the Transmit
Frame Status. No retry attempt will be scheduled on
detection of a late collision, and the XMTFIFO will be
flushed. The late collision condition will cause the
de-assertion of TDTREQ, and the assertion of the
INTR pin, providing the XMTINTM bit is cleared.
If a receive message suffers a collision, it will be either
a runt, in which case it will be deleted in the Receive
FIFO, or it will be marked as a receive late collision,
using the CLSN bit in the Receive Frame Status register. All frames which suffer a collision within the slot
time will be deleted in the Receive FIFO without
requesting host intervention, providing that the LLRCV
bit (Receive Frame Control) is not set. Runt packets
which suffer a collision will be aborted regardless of the
state of the RPA bit (User Test Register). If the collision
commences after the slot time, the MACE device
receiver will stop sending collided packet data to the
Receive FIFO and the packet data read by the system
will contain the amount of data received to the point of
collision; the CLSN bit in the Receive Frame Status
register will indicate the receive late collision. Note that
the Receive Message Byte Count will report the total
number of bytes during the receive activity, including
the collision.
The IEEE 802.3 Standard requires use of a truncated
binary exponential backoff algorithm which provides a
controlled pseudo random mechanism to enforce the
collision backoff interval, before re-transmission is
attempted.
In all normal receive collision cases, the MACE device
eliminates the transfer of packet data across the host
bus. In a receive late collision condition, the MACE chip
minimizes the amount transferred. These functions
preserve bus bandwidth utilization.
See ANSI/IEEE Std 802.3-1990 Edition, 4.2.3.2.5:
Manchester Encoder/Decoder (MENDEC)
“At the end of enforcing a collision (jamming),
the CSMA/CD sublayer delays before attempting to re-transmit the frame. The delay is an integer multiple of slotTime. The number of slot
times to delay before the nth re-transmission
attempt is chosen as a uniformly distributed
random integer r in the range:
The integrated Manchester Encoder/Decoder provides
the PLS (Physical Signaling) functions required for a
fully compliant IEEE 802.3 station. The MENDEC block
contains the AUI, DAI interfaces, and supports the
10BASE-T interface; all of which transfer data to appropriate transceiver devices in Manchester encoded format. The MENDEC provides the encoding function for
data to be transmitted on the network using the high
accuracy on-board oscillator, driven by either the crystal oscillator or an external CMOS level compatible
clock generator. The MENDEC also provides the
decoding function from data received from the network.
The MENDEC contains a Power On Reset (POR)
circuit, which ensures that all analog portions of the
MACE device are forced into their correct state during
power up, and prevents erroneous data transmission
and/or reception during this time.
0 ≤ r ≤ 2k, where k = min (n,10).“
The MACE device implements a random number
g e n e r a t o r, c o n f i g u r e d t o e n s u r e t h a t n o d e s
experiencing a collision, will not have their retry intervals track identically, causing retry errors.
The MACE device provides an alternative algorithm,
which suspends the counting of the slot time/IPG during the time that receive carrier sense is detected. This
aids in networks where large numbers of nodes are
present, and numerous nodes can be in collision. It
effectively accelerates the increase in the backoff time
in busy networks, and allows nodes not involved in the
collision to access the channel whilst the colliding
nodes await a reduction in channel activity. Once chan-
38
External Crystal Characteristics
When using a crystal to drive the oscillator, the following crystal specification should be used to ensure less
than ±0.5 ns jitter at DO±
Am79C940
Parameter
Min
Nom
1. Parallel Resonant Frequency
2. Resonant Frequency Error
(CL = 20 pF)
Max
20
Units
MHz
–50
+50
PPM
–40
+40
PPM
20
pF
3. Change in Resonant Frequency
With Respect To Temperature (CL = 20
pF)*
4. Crystal Capacitance
5. Motional Crystal Capacitance (C1)
0.022
pF
6. Series Resistance
35
ohm
7. Shunt Capacitance
7
pF
* Requires trimming crystal spec; no trim is 50 ppm total
External Clock Drive Characteristics
When driving the oscillator from an external clock
source, XTAL2 must be left floating (unconnected). An
external clock having the following characteristics must
be used to ensure less than ±0.5 ns jitter at DO±.
Clock Frequency:
Rise/Fall Time (tR/tF):
20 MHz ±0.01%
< 6 ns from 0.5 V
to VDD–0.5
XTAL1 HIGH/LOW Time
40 – 60%
(tHIGH/tLOW):
duty cycle
XTAL1 Falling Edge to
< ±0.2 ns at
Falling Edge Jitter:
2.5 V input (VDD/2)
also used as a stable bit rate clock by the receive
section of the SIA and controller.
The oscillator requires an external 0.005% crystal, or
an external 0.01% CMOS-level input as a reference.
The accuracy requirements if an external crystal is
used are tighter because allowance for the on-chip
oscillator must be made to deliver a final accuracy of
0.01%.
Transmission is enabled by the controller. As long as
the ITENA request remains active, the serial output of
the controller will be Manchester encoded and appear
at DO±. When the internal request is dropped by the
controller, the differential transmit outputs go to one of
two idle states, dependent on TSEL in the Mode
Register (CSR15, bit 9):
MENDEC Transmit Path
TSEL LOW:
The transmit section encodes separate clock and NRZ
data input signals into a standard Manchester encoded
serial bit stream. The transmit outputs (DO ± ) are
designed to operate into terminated transmission lines.
When operating into a 78 ohm terminated transmission
line, signaling meets the required output levels and
skew for Cheapernet, Ethernet and IEEE-802.3.
Transmitter Timing and Operation
A 20 MHz fundamental mode crystal oscillator provides
the basic timing reference for the SIA portion of the
MACE device. It is divided by two, to create the internal
transmit clock reference. Both clocks are fed into the
SIA’s Manchester Encoder to generate the transitions
in the encoded data stream. The internal transmit clock
is used by the SIA to internally synchronize the Internal
Transmit Data (ITXD) from the controller and Internal
Transmit Enable (ITENA). The internal transmit clock is
The idle state of DO± yields “zero”
differential to operate transformercoupled loads.
TSEL HIGH:
In this idle state, DO+ is positive with
respect to DO– (logical\HIGH).
Receive Path
The principal functions of the Receiver are to signal the
MACE device that there is information on the receive
pair, and separate the incoming Manchester encoded
data stream into clock and NRZ data.
The Receiver section (see Receiver Block Diagram)
consists of two parallel paths. The receive data path is
a zero threshold, wide bandwidth line receiver. The
carrier path is an offset threshold bandpass detecting
line receiver. Both receivers share common bias networks to allow operation over a wide input common
mode range.
Am79C940
39
DI±
Data
Receiver
Manchester
Decoder
Noise
Reject
Filter
Carrier
Detect
Circuit
Receiver Block Diagram
Input Signal Conditioning
Transient noise pulses at the input data stream
are rejected by the Noise Rejection Filter. Pulse width
rejection is proportional to transmit data rate. DC
inputs more negative than minus 100 mV ar e
also suppressed.
The Carrier Detection circuitry detects the presence of
an incoming data packet by discerning and rejecting
noise from expected Manchester data, and controls the
stop and start of the phase-lock loop during clock
acquisition. Clock acquisition requires a valid
Manchester bit pattern of 1010 to lock onto the
incoming message.
When input amplitude and pulse width conditions are
met at DI±, the internal enable signal from the SIA to
controller (RXCRS) is asserted and a clock acquisition
cycle is initiated.
Clock Acquisition
When there is no activity at DI± (receiver is idle), the
receive oscillator is phase locked to TCK. The first negative clock transition (bit cell center of first valid
Manchester “0") after RXCRS is asserted interrupts the
receive oscillator. The oscillator is then restarted at the
second Manchester “0" (bit time 4) and is phase locked
to it. As a result, the SIA acquires the clock from the
incoming Manchester bit pattern in 4 bit times with a
“1010" Manchester bit pattern.
SRDCLK and SRD are enabled 1/4 bit time after clock
acquisition in bit cell 5 if the ENPLSIO bit is set in the
PLS configuration control register. SRD is at a HIGH
state when the receiver is idle (no SRDCLK). SRD
however, is undefined when clock is acquired and may
remain HIGH or change to LOW state whenever
SRDCLK is enabled. At 1/4 bit time through bit cell 5,
40
SRD
SRDCLK
RXCRS
16235D-5
the controller portion of the MACE device sees the first
SRDCLK transition. This also strobes in the incoming
fifth bit to the SIA as Manchester “1". SRD may make a
transition after the SRDCLK rising edge bit cell 5, but
its state is still undefined. The Manchester “1" at bit 5 is
clocked to SRD output at 1/4 bit time in bit cell 6.
PLL Tracking
After clock acquisition, the phase-locked clock is compared to the incoming transition at the bit cell center
(BCC) and the resulting phase error is applied to a
correction circuit. This circuit ensures that the
phase-locked clock remains locked on the received
signal. Individual bit cell phase corrections of the Voltage Controlled Oscillator (VCO) are limited to 10%
of the phase differencebetween BCCand phaselocked clock.
Carrier Tracking and End of Message
The carrier detection circuit monitors the DI± inputs
after RXCRS is asserted for an end of message.
RXCRS de-asserts 1 to 2 bit times after the last positive
transition on the incoming message. This initiates the
end of reception cycle. The time delay from the last rising edge of the message to RXCRS deassert allows
the last bit to be strobed by SRDCLK and transferred to
the controller section, but prevents any extra bit(s) at
the end of message. When IRENA de-asserts (see
Receive Timing-End of Reception (Last Bit = 0) and
Receive Timing-End of Reception (Last Bit = 1) waveform diagrams) an RXCRS hold off timer inhibits
RXCRS assertion for at least 2 bit times.
Data Decoding
The data receiver is a comparator with clocked output
to minimize noise sensitivity to the DI± inputs. Input
error is less than ± 35 mV to minimize sensitivity to
Am79C940
input rise and fall time. SRDCLK strobes the data
receiver output at 1/4 bit time to determine the value of
the Manchester bit and clocks the data out on SRD on
the following SRDCLK. The data receiver also generates the signal used for phase detector comparison to
the internal SIA voltage controlled oscillator (VCO).
Differential Input Terminations
The differential input for the Manchester data (DI±) is
externally terminated by two 40.2 ohm ±1% resistors
and one optional common-mode bypass capacitor, as
shown in the Differential Input Termination diagram
below. The differential input impedance, ZIDF, and the
common-mode input impedance, ZICM, are specified
so that the Ethernet specification for cable termination
impedance is met using standard 1% resistor terminators. If SIP devices are used, 39 ohms is also a suitable
value. The CI ± differential inputs are terminated in
exactly the same way as the DI± pair.
AUI Isolation
Transformer
DI+
CURIO
DI
40.2 Ω
40.2 Ω
0.01µF
16235D-6
Differential Input Termination
Collision Detection
A transceiver detects the collision condition on the network and generates a differential signal at the CI±
inputs. This collision signal passes through an input
stage which detects signal levels and pulse duration.
When the signal is detected by the MENDEC, it sets
the CLSN line HIGH. The condition continues for approximately 1.5 bit times after the last LOW-to-HIGH
transition on CI±.
Jitter Tolerance Definition
The Receive Timing-Start of Reception Clock Acquisition waveform diagram shows the internal timing relationships implemented for decoding Manchester data
in the SIA module. The SIA utilizes a clock capture
circuit to align its internal data strobe with an incoming
bit stream. The clock acquisition circuitry requires four
valid bits with the values 1010. Clock is phase locked
to the negative transition at the bit cell center of the
second “0" in the pattern.
Since data is strobed at 1/4 bit time, Manchester transitions which shift from their nominal placement
through 1/4 bit time will result in improperly decoded
data. With this as the criteria for an error, a definition of
“Jitter Handling” is:
The peak deviation approaching or crossing 1/4 bit cell
position from nominal input transition, for which the SIA
section will properly decode data.
Attachment Unit Interface (AUI)
The AUI is the PLS (Physical Signaling) to PMA (Physical Medium Attachment) interface which effectively
connects the DTE to the MAU. The differential interface
provided by the MACE device is fully compliant to
Section 7 of ISO 8802-3 (ANSI/IEEE 802.3).
After the MACE device initiates a transmission it will
expect to see data looped-back on the DI± pair (AUI
port selected). This will internally generate a carrier
sense, indicating that the integrity of the data path to
and from the MAU is intact, and that the MAU is operating correctly. This carrier sense signal must be
asserted during the transmission when using the AUI
port (DO ± transmitting). If carrier sense does not
become active in response to the data transmission, or
becomes inactive before the end of transmission, the
loss of carrier (LCAR) error bit will be set in the Trans-
Am79C940
41
mit Frame Status (bit 7) after the packet has been
transmitted.
Digital Attachment Interface (DAI)
The Digital Attachment Interface is a simplified electrical attachment specification which allows MAUs which
do not require the DC isolation between the MAU and
DTE (e.g. devices compatible with the 10BASE-T Standard and 10BASE-FL Draft document) to be implemented. All data transferred across the DAI port is
Manchester Encoded. Decoding and encoding is
performed by the MENDEC.
The DAI port will accept receive data on the basis that
the RXCRS input is active, and will take the data presented on the RXDAT input as valid Manchester data.
Transmit data is sent to the external transceiver by the
MACE device asserting TXEN and presenting complimentary data on the TXDAT± pair. During idle, the
MACE device will assert the TXDAT+ line high, and the
TXDAT line low, while TXEN is maintained inactive
(high). The MACE device implements logical collision
detection and will use the simultaneous assertion of
TXEN and RXCRS to internally detect a collision condition, take appropriate internal action (such as abort
the current transmit or receive activity), and provide
external indication using the CLSN pin. Any external
transceiver utilized for the DAI interface must not loop
back the transmit data (presented by the MACE device) on the TXDAT± pins to the RXDAT pin. Neither
should the transceiver assert the RXCRS pin when
transmitting data to the network. Duplication of these
functions by the external transceiver (unless the MACE
device is in the external loop back test configuration)
will cause false collision indications to be detected.
In order to provide an integrity test of the connectivity
between the MACE device and the external transceiver
similar to the SQE Test Message provided as a part of
the AUI functionality, the MACE device can be programmed to operate the DAI port in an external loopback test. In this case, the external transceiver is
assumed to loopback the TXDAT± data stream to the
RXDAT pin, and assert RXCRS in response to the
TXEN request. When in the external loopback mode of
operation (programmed by LOOP [1-0] = 01), the
MACE device will not internally detect a collision condition. The external transceiver is assumed to take action
to ensure that this test will not disrupt the network. This
type of test is intended to be operated for a very limited
period (e.g. after power up), since the transceiver is assumed to be located physically close to the MACE
device and with minimal risk of disconnection (e.g. connected via printed circuit board traces).
Note that when the DAI port is selected, LCAR errors
will not occur, since the MACE device will internally loop
back the transmit data path to the receiver. This loop
back function must not be duplicated by a transceiver
42
which is externally connected via the DAI port, since this
will result in a condition where a collision is generated
during any transmit activity.
The transmit function of the DAI port is protected by a
jabber mechanism which will be invoked if the TXDAT±
and TXEN circuit is active for an excessive period (20 150 ms). This prevents a single node from disrupting
the network due to a stuck-on or faulty transmitter. If
this maximum transmit time is exceeded, the DAI port
transmitter circuitry is disabled, the CLSN pin is
asserted, the Jabber bit (JAB in the Interrupt Register)
is set and the INTR pin will be asserted providing the
JABM bit (Interrupt Mask Register) is cleared. Once the
internal transmit data stream from the MENDEC stops
(TXEN deasserts), an unjab time of 250 ms-750 ms will
elapse before the MACE device deasserts the CLSN
indication and re-enables the transmit circuitry.
When jabber is detected, the MACE device will assert
the CLSN pin, de-assert the TXEN pin (regardless of
internal MENDEC activity) and set the TXDAT+ and
TXDAT pins to their inactive state.
10BASE-T Interface
Twisted Pair Transmit Function
Data transmission over the 10BASE-T medium
requires use of the integrated 10BASE-T MAU, and
uses the differential driver circuitry in the TXD± and
TXP± pins. The driver circuitry provides the necessary
electrical driving capability and the pre-distortion control for transmitting signals over maximum length
Twisted Pair cable, as specified by the 10BASE-T
supplement to the IEEE 802.3 Standard. The transmit
function for data output meets the propagation delays
and jitter specified by the standard. During normal
transmission, and providing that the 10BASE-T MAU is
not in a Link Fail or jabber state, the TXEN pin will
be driven HIGH and can be used indirectly to drive a
status LED.
Twisted Pair Receive Function
The receiver complies with the receiver specifications
of the IEEE 802.3 10BASE-T Standard, including noise
immunity and received signal rejection criteria (Smart
Squelch). Signals meeting this criteria appearing at the
RXD± differential input pair are routed to the internal
MENDEC. The receiver function meets the propagation delays and jitter requirements specified by the
10BASE-T Standard. The receiver squelch level drops
to half its threshold value after unsquelch to allow
reception of minimum amplitude signals and to mitigate
carrier fade in the event of worst case signal attenuation and crosstalk noise conditions. During receive, the
RXCRS pin is driven HIGH and can be used indirectly
to drive a status LED.
Note that the 10BASE-T Standard defines the receive input
amplitude at the external Media Dependent Interface
Am79C940
(MDI). Filter and transformer loss are not specified. The
10BASE-T MAU receiver squelch levels are defined to account for a 1dB insertion loss at 10 MHz, which is typical for
the type of receive filters/transformers recommended (see
the Appendix for additional details).
Normal 10BASE-T compatible receive thresholds are
employed when the LRT bit is inactive (PHY Configuration Control register). When the LRT bit is set, the
Low Receive Threshold option is invoked, and the sensitivity of the 10BASE-T MAU receiver is increased.
This allows longer line lengths to be employed, exceeding the 100m target distance of normal 10BASE-T
(assuming typical 24 AWG cable). The additional cable
distance attributes directly to increased signal attenuation and reduced signal amplitude at the 10BASE-T
MAU receiver. However, from a system perspective,
making the receiver more sensitive means that it is also
more susceptible to extraneous noise, primarily caused
by coupling from co-resident services (crosstalk). For
this reason, it is recommended that when using the
Low Receive Threshold option that the service should
be installed on 4-pair cable only. Multi-pair cables
within the same outer sheath have lower crosstalk attenuation, and may allow noise emitted from adjacent
pairs to couple into the receive pair, and be of sufficient
amplitude to falsely unsquelch the 10BASE-T
MAU receiver.
Link Test Function
The link test function is implemented as specified by
10BASE-T standard. During periods of transmit pair
inactivity, Link Test pulses will be periodically sentover
the twisted pair medium to constantly monitor
medium integrity.
When the link test function is enabled, the absence of
Link Test pulses and receive data on the RXD± pair will
cause the 10BASE-T MAU to go into a Link Fail state.
In the Link Fail state, data transmission, data reception,
data loopback and the collision detection functions are
disabled, and remain disabled until valid data or >5
consecutive link pulses appear on the RXD± pair. During Link Fail, the LNKST pin is inactive (externally
pulled HIGH), and the Link Fail bit (LNKFL in the PHY
Configuration Control register) will be set. When the
link is identified as functional, the LNKST pin is driven
LOW (capable of directly driving a Link OK LED using
an integrated 12 mA driver) and the LNKFL bit will be
cleared. In order to inter-operate with systems which
do not implement link test, this function can be disabled
by setting the the Disable Link Test bit (DLNKTST in the
PHY Configuration Control register). With link test
disabled, the data driver, receiver and loopback functions as well as collision detection remain enabled
irrespective of the presence or absence of data or link
pulses on the RXD± pair.
The MACE devices integrated 10BASE-T transceiver
will mimic the performance of an externally connected
device (such as a 10BASE-T MAU connected using an
AUI). When the 10BASE-T transceiver is in link fail, the
receive data path of the transceiver must be disabled.
The MACE device will report a Loss of Carrier error
(LCAR bit in the Transmit Frame Status register) due to
the absence of the normal loopback path, for every
packet transmitted during the link fail condition. In addition, a Collision Error (CERR bit in the Transmit
Frame Status register) will also be reported (see the
section on Signal Quality Error Test Function for
additional details).
If the AWAKE bit is set in the PHY Configuration Control register prior to the assertion of the hardware
SLEEP pin, the 10BASE-T receiver remains operable,
and is able to detect and indicate (using the LNKST
output) the presence of legitimate Link Test pulses or
receive activity. The transmission of Link Test pulses is
suspended to reduce power consumption.
If the RWAKE bit is set in the PHY Configuration Control register prior to the assertion of the hardware
SLEEP pin, the 10BASE-T receiver and transmitter
functions remain active, the LNKST output is disabled,
and the EADI output pins are enabled. In addition the
AUI port (transmit and receive) remains active. Note
that since the MAC core will be in a sleep mode, no
transmit activity is possible, and the transmission of
Link Test pulses is also suspended to reduce
power consumption.
Polarity Detection and Reversal
The Twisted Pair receive function includes the ability to
invert the polarity of the signals appearing at the RXD±
pair if the polarity of the received signal is reversed
(such as in the case of a wiring error). This feature allows data packets received from a reverse wired RXD±
input pair to be corrected in the 10BASE-T MAU prior
to transfer to the MENDEC. The polarity detection function is activated following reset or Link Fail, and will
reverse the receive polarity based on both the polarity
of any previous Link Test pulses and the polarity of
subsequent packets with a valid End Transmit
Delimiter (ETD).
When in the Link Fail state, the internal 10BASE-T
receiver will recognize Link Test pulses of either positive or negative polarity. Exit from the Link Fail state is
made due to the reception of five to six consecutive
Link Test pulses of identical polarity. On entry to the
Link Pass state, the polarity of the last five Link Test
pulses is used to determine the initial receive polarity
configuration and the receiver is reconfigured to subsequently recognize only Link Test pulses of the previously recognized polarity. This link pulse algorithm is
employed only until ETD polarity determination is made
as described later inthis section.
Am79C940
43
Positive Link Test pulses are defined as received signal
with a positive amplitude greater than 520 mV (LRT =
LOW) with a pulse width of 60 ns-200 ns. This positive
excursion may be followed by a negative excursion.
This definition is consistent with the expected received
signal at a correctly wired receiver, when a Link Test
pulse which fits the template of Figure 14-12 in the
10BASE-T Standard is generated at a transmitter and
passed through 100 m of twisted pair cable.
Negative Link Test pulses are defined as received signals with a negative amplitude greater than 520 mV
(LRT = LOW) with a pulse width of 60 ns-200 ns. This
negative excursion may be followed by a positive excursion. This definition is consistent with the expected
received signal at a reverse wired receiver, when a
Link Test pulse which fits the template of Figure 14-12
in the 10BASE–T Standard is generated at a transmitter and passed through 100 m of twisted pair cable.
The polarity detection/correction algorithm will remain
armed until two consecutive packets with valid ETD of
identical polarity are detected. When armed, the
receiver is capable of changing the initial or previous
polarity configuration based on the most recent ETD
polarity.
On receipt of the first packet with valid ETD following
reset or Link Fail, the MACE device will utilize the
inferred polarity information to configure its RXD ±
input, regardless of its previous state. On receipt of a
second packet with a valid ETD with correct polarity,
the detection/correction algorithm will lock-in the
received polarity. If the second (or subsequent) packet
is not detected as confirming the previous polarity
decision, the most recently detected ETD polarity will
be used as the default. Note that packets with invalid
ETD have no effect on updating the previous polarity
decision. Once two consecutive packets with valid ETD
have been received, the MACE device will disable the
detection/correction algorithm until either a Link Fail
condition occurs or a hardware or software reset
occurs.
During polarity reversal, the RXPOL pin should be
externally pulled HIGH and the Reversed Polarity bit
(REVPOL in the PHY Configuration Control register)
will be set. During normal polarity conditions, the
RXPOL pin is driven LOW (capable of directly driving a
Polarity OK LED using an integrated 12 mA driver) and
the REVPOL bit will be cleared.
If desired, the polarity correction function can be disabled by setting the Disable Auto Polarity Correction bit
(DAPC bit in the PHY Configuration Control register).
However, the polarity detection portion of the algorithm
continues to operate independently, and the RXPOL
pin and the REVPOL bits will reflect the polarity state of
the receiver.
44
Twisted Pair Interface Status
Three outputs (TXEN, RXCRS and CLSN) indicate
whether the MACE device is transmitting (MENDECto
Twisted Pair), receiving (Twisted Pair to MENDEC), or
in a collision state with both func tions activ e
simultaneously.
The MACE device will power up in the Link Fail state.
The normal algorithm will apply to allow it to enter the
Link Pass state. On power up, the TXEN, RXCRS and
CLSN) pins will be in a high impedance state until they
are enabled by setting the Enable PLS I/O bit
(ENPLSIO in the PLS Configuration Control register)
and the 10BASE-T port enters the Link Pass state.
In the Link Pass state, transmit or receive activity which
passes the pulse width/amplitude requirements of the
DO± or RXD± inputs, will be indicated by the TXEN or
RXCRS pin respectively going active. TXEN, RXCRS
and CLSN are all asserted during a collision.
In the Link Fail state, TXEN, RXCRS and CLSN
are inactive.
In jabber detect mode, the MACE device will activate
the CLSN pin, disable TXEN (regardless of Manchester data output from the MENDEC), and allow the
RXCRS pin to indicate the current state of the RXD±
pair. If there is no receive activity on RXD±, only CLSN
will be active during jabber detect. If there is RXD± activity, both CLSN and RXCRS will be active.
If the SLEEP pin is asserted (regardless of the programming of the AWAKE or RWAKE bits in the PHY
Configuration Control register), the TXEN, RXCRS and
CLSN outputs will be placed in a high impedance state.
Collision Detect Function
Simultaneous activity (presence of valid data signals)
from both the internal MENDEC transmit function (indicated externally by TXEN active) and the twisted pair
RXD± pins constitutes a collision, thereby causing an
external indication on the CLSN pin, and an internal
indication which is returned to the MAC core. The
TXEN, RXCRS and CLSN pins are driven high during
collision.
Signal Quality Error (SQE) Test (Heartbeat)
Function
The SQE Test message (a 10 MHz burst normally
returned on the AUI CI± pair at the end of every transmission) is intended to be a self-test indication to the
DTE that the MAU collision circuitry is functional and
the AUI cable/connection is intact. This has minimal
relevance when the 10BASE-T MAU is embedded in
the LAN controller. A Collision Error (CERR bit in the Interrupt Register) will be reported only when the
10BASE-T port is in the link fail state, since the collision
circuit of the MAU will be disabled, causing the
absence of the SQE Test message. In GPSI mode the
Am79C940
external encoder/decoder is responsible for asserting
the CLSN pin after each transmission. In DAI mode,
SEQ Test has no relevance.
Jabber Function
The Jabber function inhibits the twisted pair transmit
function of the MACE device if the TXD±/TXP± circuits
are active for an excessive period (20-150 ms). This
prevents any one node from disrupting the network due
to a stuck-on or faulty transmitter. If this maximum
transmit time is exceeded, the data path through the
10BASE-T transmitter circuitry is disabled (although
Link Test pulses will continue to be sent), the CLSN pin
is asserted, the Jabber bit (JAB in the Interrupt Register) is set and the INTR pin will be asserted providing
the JABM bit (Interrupt Mask Register) is cl eared.
Once the internal transmit data stream from the MENDEC stops (TXEN deasserts), an unjab time of
250-750 ms will elapse before the MACE device
deasserts the CLSN indication and re-enables the
transmit circuitry.
When jabber is detected, the MACE device will assert
the CLSN pin, de-assert the TXEN pin (regardless of
internal MENDEC activity), and allow the RXCRS pin to
indicate the current state of the RXD± pair. If there is no
receive activity on RXD±, only CLSN will be active during jabber detect. If there is RXD± activity, both CLSN
and RXCRS will be active.
External Address Detection Interface
(EADI)
This interface is provided to allow external perfect address filtering. This feature is typically utilized for terminal server, bridge and/or router type products. The use
of external logic is required, to capture the serial bit
stream from the MACE device, and compare this with
a table of stored addresses or identifiers. See the EADI
port diagram in the Systems Applications section,
Network Interfaces sub-section, for details.
The EADI interface operates directly from the NRZ
decoded data and clock recovered by the Manchester
decoder. This allows the external address detection to
be performed in parallel with frame reception and
address comparison in the MAC Station Address
Detection (SAD) block.
SRDCLK is provided to allow clocking of the receive bit
stream from the MACE device, into the external
address detection logic. Once a received packet commences and data and clock are available from the
decoder, the EADI interface logic will monitor the alternating (1,0) preamble pattern until the two ones of the
Start Frame Delimiter (1,0,1,0,1,0,1,1) are detected, at
which point the SF/BD output will be driven high.
After SF/BD is asserted the serial data from SRD
should be de-serialized and sent to a Content
Addressable Memory (CAM) or other address
detection device.
To allow simple serial to parallel conversion, SF/BD is
provided as a strobe and/or marker to indicate the
delineation of bytes, subsequent to the SFD. This feature provides a mechanism to allow not only capture
and/or decoding of the physical or logical (group)
address, but also facilitates the capture of header
information to determine protocol and or inter-networking information. The EAM/R pin is driven by the external address comparison logic, to either reject or accept
the packet. Two alternative modes are permitted, allowing the external logic to either accept the packet
based on address match, or reject the packet if there is
no match. The two alternate methods are programmed
using the Match/Reject (M/R) bit in the Receive Frame
Control register.
If the M/R bit is set, the pin is configured as EAM
(External Address Match). The MACE device can be
configured with Physical, Logical or Broadcast Address
comparison operational. If an internal address match is
detected, the packet will be accepted regardless of the
condition of EAM. Additional addresses can be located
in the external address detection logic. If a match is
detected, EAM must go active within 600 ns of the last
bit in the destination address field (end of byte 6) being
presented on the SRD output, to guarantee frame
reception. In addition, EAM must go inactive after a
match has been detected on a previous packet, before
the next match can take place on any subsequent
packet. EAM must be asserted for a minimum pulse
width of 200 ns.
If the M/R bit is clear (default state after either the
RESET pin or SWRST bit have been activated), the pin
is configured as EAR (External Address Reject). The
MACE device can be configured with Physical, Logical
or Broadcast Address comparison operational. If an
internal address match is detected, the packet will be
accepted regardless of the condition of EAR. Incoming
packets which do not pass the internal address comparison will continue to be received by the MACE
device. EAR must be externally presented to the
MACE chip prior to the first assertion of RDTREQ, to
guarantee rejection of unwanted packets. This allows
approximately 58 byte times after the last destination
address bit is available to generate the EAR signal, assuming the MACE device is not configured to accept
runt packets. EAR will be ignored by the MACE device
from 64 byte times after the SFD, and the packet will be
accepted if EAR has not been asserted before this
time. If the MACE device is configured to accept runt
packets, the EAR signal must be generated prior to the
receive message completion, which could be as short
as 12 byte times (assuming six bytes for source
address, two bytes for length, no data, four bytes for
FCS) after the last bit of the destination address is
Am79C940
45
available. EAR must have a pulse width of at least
200 ns.
Note that setting the PROM bit (MAC Configuration
Control) will cause all receive packets to be received,
regardless of the programming of M/R or the state of
the EAM/R input. The following table summarizes the
operation of the EADI features.
Internal/External Address Recognition Capabilities
PROM
M/R
EAM/R
Required Timing
Received Messages
1
X
X
No timing requirements
All Received Frames
0
0
H
No timing requirements
All Received Frames
0
0
↓
Low for 200 ns within 512-bits after SFD
Physical/Logical/Broadcast Matches
0
1
H
No timing requirements
Physical/Logical/Broadcast Matches
0
1
↓
Low for 200 ns within 8-bits after DA field
All Received Frames
General Purpose Serial Interface (GPSI)
The GPSI port provides the signals necessary to
present an interface consistent with the non encoded
data functions observed to/from a LAN controller such
as the Am7990 Local Area Network Controller for
Ethernet (LANCE). The actual GPSI pins are functionally identical to some of the pins from the DAI and the
EADI ports, the GPSI replicates this type of interface.
The GPSI allows use of an external Manchester
encoder/decoder, such as the Am7992B Serial Interface Adapter (SIA). In addition, it allows the MACE
device to be used as a MAC sublayer engine in a
repeater based on the Am79C980 Integrated Multiport
Repeater (IMR). Simple connection to the IMR Expansion Bus allows the MAC to view all packet data passing through a number of interconnected IMRs, allowing
statistics and network management information to
be collected.
The GPSI functional pins are duplicated as follows:
Pin Configuration for GPSI Function
Function
Receive Data
Receive Clock
Receive Carrier Sense
Collision
Transmit Data
Transmit Clock
Transmit Enable
Type
I
I
I
I
O
I
O
LANCE
Pin
RX
RCLK
RENA
CLSN
TX
TCK
TENA
MACE
Pin
RXDAT
SRDCLK
RXCRS
CLSN
TXDAT+
STDCLK
TXEN
ers DI ±, CI ±), and the crystal input (XTAL1/XTAL2)
pins, are not tested.
The following is a brief summary of the IEEE 1149.1
compatible test functions implemented in the MACE
device. For additional details, consult the IEEE Standard Test Access Port and Boundary-Scan Architecture document (IEEE Std 1149.1–1990).
The boundary scan test circuit requires four pins (TCK,
TMS, TDI and TDO ), defined as the Test Access Port
(TAP). It includes a finite state machine (FSM), an
instruction register, a data register array and a power
on reset circuit. Internal pull-up resistors are provided
for the TCK, TDI and TMS pins.
The TAP engine is a 16 state FSM, driven by the Test
Clock (TCK) and the Test Mode Select (TMS) pins. An
independent power on reset circuit is provided to
ensure the FSM is in the TEST_LOGIC_RESET state
at power up.
In addition to the minimum IEEE 1149.1 instruction
requirements (EXTEST, SAMPLE and BYPASS), three
additional instructions (IDCODE, TRI_ST and SET_I/
O) are provided to further ease board level testing. All
unused instruction codes are reserved.
IEEE 1149.1 Supported Instruction Summary
Inst
ame
Description
EXTEST External Test
Selected
Data Reg
Reg
Mode
Inst
Code
BSR
Test
0000
IDCode
ID Code Inspection
ID Reg
Normal 0001
IEEE 1149.1 Test Access Port Interface
Sample
Sample Boundary
BSR
Normal 0010
An IEEE 1149.1 compatible boundary scan Test
Access Port is provided for board level continuity test
and diagnostics. All digital input, output and input/output and input/output pins are tested. Analog pins,
including the AUI differential driver (DO±) and receiv-
TRI_ST
Force Tristate
Bypass
Normal 0011
SET_I/0
Control
BoundaryTo I/0
Bypass
Test
0100
Bypass
Bypass Scan
Bypass
Normal
1111
46
Am79C940
After hardware or software reset, the IDCODE instruction is always invoked. The decoding logic provides
signals to control the data flow in the DATA registers
according to the current instruction.
Each Boundary Scan Register (BSR) cell also has two
stages. A flip-flop and a latch are used in the SERIAL
SHIFT STAGE and the PARALLEL OUTPUT STAGE
respectively.
There are four possible operational modes in the BSR
cell:
1. CAPTURE
TC can be dynamically changed on a cycle by cycle
basis to program the slave cycle execution for two (TC
= HIGH) or three (TC = LOW) SCLK cycles. TC must
be stable by the falling edge of SCLK (EDSEL = High)
in S0 at the start of a cycle, and should only be
changed in S0 in a multiple cycle burst.
A read cycle is initiated when either CS or FDS is sampled low on the falling edge of SCLK at S0. FDS and
CS must be asserted exclusively. If they are active
simultaneously when sampled, the MACE device will
not execute any read or write cycle.
If CS is low, a Register Address read will take place.
The state of the ADD4–0 will be used to commence
decoding of the appropriate internal register/FIFO.
2. SHIFT
3. UPDATE
If FDS is low, a FIFO Direct read will take place from
the RCVFIFO. The state of the ADD4-0 bus is irrelevant for the FIFO Direct mode.
4. SYSTEM FUNCTION
Other Data Registers
■ BYPASS REG (1 bit)
With either the CS or FDS input active, the state of the
ADD0-4 (for Register Address reads), R/W (high to
indicate a read cycle), BE0 and BE1 will also be latched
on the falling (EDSEL = HIGH) edge of SCLK at S0.
■ Device Identification Register (32 bits)
Bits 31-28:Version (4 bits)
Bits 27-12:Part number (16 bits) is 9400H
Bits 11-1:Manufacturer ID (11 bits).
The manufacturer ID code for AMD is
00000000001 in accordance with
JEDEC Publication 106-A.
Bit 0:Always a logic 1
SLAVE ACCESS OPERATION
Internal register accesses are based on a 2 or 3 SCLK
cycle duration, dependent on the state of the TC input
pin. TC must be externally pulled low to force the
MACE device to perform a 3-cycle access. TC is internally pulled high if left unconnected, to configure the
2-cycle access by default.
All register accesses are byte wide with the exception
of the data path to and from the internal FIFOs.
Data exchanges to/from register locations will take
place over the appropriate half of the data bus to suit
the host memory organization (as programmed by the
BSWP bit in the BIU Configuration Control register).
The BE0, BE1 and EOF signals are provided to allow
control of the data flow to and from the FIFOs. Byte
read operations from the Receive FIFO cause data to
be duplicated on both the upper and lower bytes of the
data bus. Byte write operations to the Transmit FIFO
must use the BE0 and BE1 inputs to define the active
data byte to the MACE device.
Read Access
Details of the read access timing are located in the AC
Waveforms section, Host System Interface, figures:
Two-Cycle Receive FIFO/Register Read Timing and
Three-Cycle Receive FIFO/Register Read Timing.
From the falling edge of SCLK in S1 (EDSEL = HIGH),
the MACE device will drive data on DBUS15-0 and
activate the DTV output (providing the read cycle completed successfully). If the cycle read the last byte/word
of data for a specific frame from the RCVFIFO, the
MACE device will also assert the EOF signal. DBUS150, DTV and EOF will be guaranteed valid and can be
sampled on the falling (EDSEL = HIGH) edge of SCLK
at S2.
If the Register Address mode is being used to access
the RCVFIFO, once EOF is asserted during the last
byte/word read for the frame, the Receive Frame Status can be read in one of two ways. The Register Address mode can be continued, by placing the
appropriate address (00110b) on the address bus and
executing four read cycles (CS active) on the Receive
Frame Status location. In this case, additional Register
Address read requests from the RCVFIFO will be ignored, and no DTV returned, until all four bytes of the
Receive Frame Status register have been read. Alternatively, a FIFO Direct read can be performed, which
will effectively route the Receive Frame Status through
the RCVFIFO location. This mechanism is explained in
more detail below.
If the FIFO Direct mode is used, the Receive Frame
Status can be read directly from the RCVFIFO by continuing to execute read cycles (by asserting FDS low
and R/W high) after EOF is asserted indicating the last
byte/word read for the frame. Each of the four bytes of
Receive Frame Status will appear on both halves of the
data bus, as if the actual Receive Frame Status register were being accessed. Alternatively, the status can
be read as normal using the Register Address mode by
Am79C940
47
placing the appropriate address (00110b) on the
address bus and executing four read cycles (CS
active).
■ Write the BIU Configuration Control (BIUCC) register to change the Byte Swap mode to big endian or
to change the Transmit Start Point.
Either the FIFO Direct or Register Address modes can
be interleaved at any time to read the Receive Frame
Status, although this is considered unlikely due to the
additional overhead it requires. In either case, no additional data will be read from the RCVFIFO until the
Receive Frame Status has been read, as four bytes
appended to the end of the packet when using the
FIFO Direct mode, or as four bytes from the Receive
Frame Status location when using the Register
Address mode.
■ Write the FIFO Configuration Control (FIFOCC)
register to change the FIFO watermarks or to
enable the FIFO Burst Mode.
EOF will only be driven by the MACE device when
reading received packet data from the RCVFIFO. At all
other times, including reading the Receive Frame Status using the FIFO Direct mode, the MACE device will
place EOF in a high impedance state.
RDTREQ should be sampled on the falling edge of
SCLK. The assertion of RDTREQ is programmed by
RCVFW, and the de-assertion is modified dependent
on the state of the RCVBRST bit (both in the FIFO Configuration Control register). See the section Receive
FIFO Read for additional details.
Write Access
Details of the write access timing are located in the AC
Waveforms section, Host System Interface, figures:
Two-Cycle Transmit FIFO/Register Write Timing and
Three-Cycle Transmit FIFO/Register Write Timing.
Write cycles are executed in a similar manner as the
read cycle previously described, but with the R/W input
low, and the host responsible to provide the data with
sufficient set up to the falling edge of SCLK after S2.
After a FIFO write, TDTREQ should be sampled on or
after the falling (EDSEL = HIGH) edge of SCLK after
S3 of the FIFO write. The state of TDTREQ at this time
will reflect the state of the XMTFIFO.
After going active (low), TDTREQ will remain low for
two or more XMTFIFO writes.
The minimum high (inactive) time of TDTREQ is one
SCLK cycle. When EOF is written to the Transmit
FIFO, TDTREQ will go inactive after one SCLK cycle,
for a minimum of one SCLK cycle.
Initialization
After power-up, RESET should be asserted for a minimum of 15 SCLK cycles to set the MACE device into a
defined state. This will set all MACE registers to their
default values. The receive and transmit functions will
be turned off. A typical sequence to initialize the MACE
device could look like this:
48
■ Write the Interrupt Mask Register (IMR) to disable
unwanted interrupt sources.
■ Write the PLS Configuration Control (PLSCC)
register to enable the active network port. If the
GPSI interface is used, the register must be written
twice. The first write access should only set
PORTSEL [1–0] = 11. The second access must
write again PORTSEL[1–0] = 11 and additionally set
ENPLSIO = 1. This sequence is required to avoid
contention on the clock, data and/or carrier indication signals.
■ Write the PHY Configuration Control (PHYCC) register to configure any non-default mode if the
10BASE-T interface is used.
■ Program the Logical Address Filter (LADRF) register or the Physical Address Register (PADR). The
Internal Address Configuration (IAC) register must
be accessed first. Set the Address Change
(ADDRCHG) bit to request access to the internal
address RAM. Poll the bit until it is cleared by the
MACE device indicating that access to the internal
address RAM is permitted. In the case of an
address RAM access after hardware or software
reset (ENRCV has not been set), the MACE device
will return ADDRCHG = 0 right away. Set the
LOGADDR bit in the IAC register to select writing to
the Logical Address Filter register. Set the PHYADDR bit in the IAC register to select writing to the
Physical Address Register. Either bit can be set together with writing the ADDRCHG bit. Initializing the
Logical Address Filter register requires 8 write
cycles. Initializing the Physical Address Register
requires 6 write cycles.
■ Write the User Test Register (UTR) to set the MACE
device into any of the user diagnostic modes such
as loopback.
■ Write the MAC Configuration Control (MACCC) register as the last step in the initialization sequence to
enable the receiver and transmitter. Note that the
system must guarantee a delay of 1 ms after
power-up before enabling the receiver and transmitter to allow the MACE phase lock loop to stabilize.
■ The Transmit Frame Control (XMTFC) and the
Receive Frame Control (RCVFC) registers can be
programmed on a per packet basis.
Am79C940
Reinitialization
The SWRST bit in the BIU Configuration Control
(BIUCC) register can be set to reset the MACE device
into a defined state for reinitialization. The same
sequence described in the initialization section can be
used. The 1 ms delay for the MACE phase lock loop
stabilization need not to be observed as it only applies
to a power-up situation.
TRANSMIT OPERATION
The transmit operation and features of the MACE
device are controlled by programmable options. These
options are programmed through the BIU, FIFO and
MAC Configuration Control registers.
Parameters controlled by the MAC Configuration Control register are generally programmed only once,
during initialization, and are therefore static during the
normal operation of the MACE device (see the Media
Access Control section for a detailed description). The
features controlled by the FIFO Configuration Control
register and the Transmit Frame Control register can
be re-programmed if the MACE device is not transmitting.
Transmit FIFO Write
The Transmit FIFO is accessed by performing a host
generated write sequence on the MACE device. See
the Slave Access Operation-Write Access section and
the AC Waveforms section, Host System Interface, figures: Two-Cycle Transmit FIFO/Register Write Timing
and Three-Cycle Transmit FIFO/Register Write Timing
for details of the write access timing.
There are two fundamentally different access methods
to write data into the FIFO. Using the Register Address
mode, the FIFO can be addressed using the ADD0-4
lines, (address 00001b), initiating the cycle with the CS
and R/W (low) signals. The FIFO Direct mode allows
write access to the Transmit FIFO without use of the
address lines, and using only the FDS and R/W lines.
If the MACE device detects both signals active, it will
not execute a write cycle. The write cycle timing for the
Register Address or Direct FIFO modes are identical.
FDS and CS should be mutually exclusive.
The data stream to the Transmit FIFO is written using
multiple byte and/or word writes. CS or FDS does not
have to be returned inactive to commence execution of
the next write cycle. If CS/FDS is detected low at the
falling edge of S0, a write cycle will commence. Note
that EOF must be asserted by the host/controller
during the last byte/word transfer.
Transmit Function Programming
The Transmit Frame Control register allows programming of dynamic transmit attributes. Automatic transmit
features such as retry on collision, FCS generation/
transmission and pad field insertion can all be
programmed, to provide flexibility in the
(re-)transmission of messages.
The disable retry on collision (DRTRY bit) and automatic pad field insertion (APAD XMT bit) features
should not be changed while data remains in the Transmit FIFO. Writing to either the DRTRY or APAD XMT
bits in this case may have unpredictable results. These
bits are not internally latched or protected. When writing to the Transmit Frame Control register the DRTRY
and APAD XMT bits should be programmed consistently. Once the Transmit FIFO is empty, DRTRY and
APAD XMT can be reprogrammed.
This can be achieved with no risk of transmit data loss
or corruption by clearing ENXMT after the packet data
for the current frame has been completely loaded. The
transmission will complete normally and the activation
of the INTR pin can be used to determine if the transmit
frame has completed (XMTINT will be set in the Interrupt Register). Once the Transmit Frame Status has
been read, APAD XMT and/or DRTRY can be changed
and ENXMT set to restart the transmit process with the
new parameters.
APAD XMT is sampled if there are less than 60 bytes
in the transmit packet when the last bit of the last byte
is transmitted. If APAD XMT is set, a pad field of pattern
00h is added until the minimum frame size of 64 bytes
(excluding preamble and SFD) is achieved. If APAD
XMT is clear, no pad field insertion will take place and
runt packet transmission is possible. When APAD XMT
is enabled, the DXMTFCS feature is over-ridden and
the four byte FCS will be added to the transmitted
packet unconditionally.
The disable FCS generation/transmission feature can
be programmed dynamically on a packet by packet
basis. The current state of the DXMTFCS bit is
internally latched on the last write to the Transmit FIFO,
when the EOF indication is asserted by the
host/controller.
The programming of static transmit attributes are distributed between the BIU, FIFO and MAC Configuration Control registers.
The point at which transmission begins in relation to
the number of bytes of a frame in the FIFO is controlled
by the XMTSP bits in the BIU Configuration Control
register. Depending on the bus latency of the system,
XMTSP can be set to ensure that the Transmit FIFO
does not underflow before more data is written to the
FIFO. When the entire frame is in the FIFO, or the FIFO
becomes full before the threshold is reached, transmission of preamble will commence regardless of the
value in XMTSP. The default value of XMTSP is 64
bytes after reset.
The point at which TDTREQ is asserted in relation to
the number of empty bytes present in the Transmit
Am79C940
49
FIFO is controlled by the XMTFW bits in the FIFO Configuration Control register. TDTREQ will be asserted
when one of the following conditions is true:
■ The number of bytes free in the Transmit FIFO relative to the current Saved Read Pointer value is
greater than or equal to the threshold set by the
XMTFW (16, 32 or 64 bytes). The Saved Read
Pointer is the first byte of the current transmit frame,
either in progress or awaiting channel availability.
■ The number of bytes free in the Transmit FIFO relative to the current Read Pointer value is greater
than or equal to the threshold set by the XMTFW
(16, 32 or 64 bytes). The Read Pointer becomes
available only after a minimum of 64 byte frame
length has been transmitted on the network (eight
bytes of preamble plus 56 bytes of data), and points
to the current byte of the frame being transmitted.
Depending on the bus latency of the system, XMTFW
can be set to ensure that the Transmit FIFO does not
underflow before more data is written into the FIFO.
When the entire frame is in the FIFO, TDTREQ will
remain asserted if sufficient bytes remain empty. The
default value of XMTFW is 64 bytes after hardware or
software reset. Note that if the XMTFW is set below the
64 byte limit, the transmit latency for the host to service
the MACE device is effectively increased, since
TDTREQ will occur earlier in the transmit sequence
and more bytes will be present in the Transmit FIFO
when the TDTREQ is de-asserted.
The transmit operation of the MACE device can be
halted at any time by clearing the ENXMT bit (bit 1) in
the MAC Configuration Control register. Note that any
complete transmit frame that is in the Transmit FIFO
and is currently in progress will complete, prior to the
transmit function halting. Transmit frames in the FIFO
which have not commenced will not be started. Transmit frames which have commenced but which have not
been fully transferred into the Transmit FIFO will be
aborted, in one of two ways. If less than 544 bits
(68 bytes) have been transmitted onto the network, the
transmission will be terminated immediately, generating a runt packet which can be deleted at the receiving
station. If greater than 544 bits have been transmitted,
the messages will have the current CRC inverted and
appended at the next byte boundary, to guarantee an
error is detected at the receiving station. This feature
ensures that packets will not be generated with potential undetected data corruption. An explanation of the
544 bit derivation appears in the “Automatic Pad
Generation” section.
Automatic Pad Generation
Transmit frames can be automatically padded to extend them to 64 data bytes (excluding preamble) permitting the minimum frame size of 64 bytes (512 bits)
for 802.3/Ethernet to be guaranteed, with no software
intervention from the host system.
APAD XMT = 1 enables the automatic padding feature.
The pad is placed between the LLC Data field and FCS
field in the 802.3 frame. The FCS is always added if
APAD XMT = 1, regardless of the state of DXMTFCS.
The transmit frame will be padded by bytes with the
value of 00h. The default value of APAD XMT will
enable auto pad generation after hardware or software
reset.
It is the responsibility of upper layer software to correctly define the actual length field contained in the
message to correspond to the total number of LLC
Data bytes encapsulated in the packet (length field as
defined in the IEEE 802.3 standard). The length value
contained in the message is not used by the MACE
device to compute the actual number of pad bytes to be
inserted. The MACE chip will append pad bytes dependent on the actual number of bits transmitted onto the
network. Once the last data byte of the frame has completed, prior to appending the FCS, the MACE device
will check to ensure that 544 bits have been transmitted. If not, pad bytes are added to extend the frame
size to this value, and the FCS is then added.
Preamble
1010....1010
SFD
10101011
Dest
Addr
Srce
Addr
Length
56
Bits
8
Bits
6
Bytes
6
Bytes
2
Bytes
IEEE 802.3 Format Data Frame
The 544 bit count is derived from the following:
50
Am79C940
LLC
Data
Pad
46—1500
Bytes
FCS
4
Bytes
16235D-7
Minimum frame size (excluding preamble,
including FCS)
64 bytes
512 bits
Preamble/SFD size
8 bytes
64 bits
FCS size
4 bytes
32bits
At the point that FCS is to be appended, the transmitted
frame should contain:
Preamble
64
A minimum length transmit frame from the MACE
device will therefore be 576 bits, after the FCS is
appended.
To be classed as a minimum size frame at the receiver,
the transmitted frame must contain:
Preamble
+
+ (Min Frame Size – FCS) bits
+
(512
– 32) bits
(Min Frame Size + FCS) bits
The Ethernet specification makes no use of the LLC
pad field, and assumes that minimum length messages
will be at least 64 bytes in length.
Preamble
1010....1010
SYNCH
11
Dest
Addr
Srce
Addr
Type
Data
FCS
62
Bits
2
Bits
6
Bytes
6
Bytes
2
Bytes
46—1500
Bytes
4
Bytes
Ethernet Format Data Frame
Transmit FCS Generation
Automatic generation and transmission of FCS for a
transmit frame depends on the value of DXMTFCS
(Disable Transmit FCS) when the EOF is asserted indicating the last byte/word of data for the transmit frame
is being written to the FIFO. The action of writing the
last data byte/word of the transmit frame, latches the
current contents of the Transmit Frame Control register, and therefore determines the programming of
DXMTFCS for the transmit frame. When DXMTFCS =
0 the transmitter will generate and append the FCS to
the transmitted frame. If the automatic padding feature
is invoked (APAD XMT in Transmit Frame Control), the
FCS will be appended regardless of the state of DXMTFCS. Note that the calculated FCS is transmitted most
significant bit first. The default value of DXMTFCS is 0
after hardware or software reset.
Transmit Status Information
Although multiple transmit frames can be queued in the
Transmit FIFO, the MACE device will not permit loss of
Transmit Frame Status information. The Transmit
Frame Status and Transmit Retry Count can only be
buffered internally for a maximum of two frames. The
MACE device will therefore not commence a third
transmit frame, until the status from the first frame is
read. Once the Transmit Retry Count and Transmit
Frame Status for the first transmit packet is read, the
MACE device will autonomously begin the next transmit frame, provided that a transmit frame is pending,
the XMTSP threshold has been exceeded (or the
16235D-8
XMT FIFO is full), the network medium is free, and the
IPG time has elapsed.
Indication of valid Transmit Frame Status can be
obtained by servicing the hardware interrupt and testing the XMTINT bit in the Interrupt Register, or by polling the XMTSV bit in the Poll register if a continuous
polling mechanism is required. If the Transmit Retry
Count data is required (for loading, diagnostic, or management information), XMTRC must be read prior to
XMTFS. Reading the XMTFS register when the
XMTSV bit is set will clear both the XMTRC and
XMTFS values.
Transmit Exception Conditions
Exception conditions for frame transmission fall into
two distinct categories; those which are the result of
normal network operation and those which occur due
to abnormal network and/or host related events.
Normal events which may occur and which are handled
autonomously by the MACE device are:
(a)
Collisions within the slot time with automatic retry
(b) Deletion of packets due to excessive transmission attempts.
(a) The MACE device will ensure that collisions which
occur within 512 bit times from the start of transmission
(including preamble) will be automatically retried with
no host intervention. The Transmit FIFO ensures this
by guaranteeing that data contained within the Trans-
Am79C940
51
mit FIFO will not be overwritten until at least 64 bytes
(512 bits) of data have been successfully transmitted
onto the network. This criteria will be met, regardless of
whether the transmit frame was the first (or only) frame
in the Transmit FIFO, or if the transmit frame was
queued pending completion of the preceding frame.
(b) If 16 total attempts (initial attempt plus 15 retries)
have been made to transmit the frame, the MACE
device will abandon the transmit process for the particular frame, de-assert the TDTREQ pin, report a Retry
Error (RTRY) in the Transmit Frame Status, and set the
XMTINT bit in the Interrupt Register, causing activation
of the external INTR pin providing the interrupt is
unmasked.
Once the XMTINT condition has been externally recognized, the Transmit Frame Counter (XMTFC) can be
read to determine whether the tail end of the frame that
suffers the RTRY error is still in the host memory (i.e.,
when XMTFC = 0). This XMTFC read should be
requested before the Transmit Frame Status read
since reading the XMTFS would cause the XMTFC to
decrement. If the tail end of the frame is indeed still in
the host memory, the host is responsible for ensuring
that the tail end of the frame does not get written into
the FIFO and does not get transmitted as a whole
frame. It is recommended that the host clear the tail
end of the frame from the host memory before requesting the XMTFS read so that after the XMTFS read,
when MACE device re-asserts TDTREQ, the tail end of
the frame does not get written into the FIFO. The
Transmit Frame Status read will indicate that the RTRY
error occurred. The read operation on the Transmit
Frame Status will update the FIFO read and write
pointers. If no End-of-Frame write (EOF pin assertion)
had occurred during the FIFO write sequence, the entire transmit path will be reset (which will update the
Transmit FIFO watermark with the current XMTFW
value in the FIFO Configuration Control register). If a
whole frame does reside in the FIFO, the read pointer
will be moved to the start of the next frame or free location in the FIFO, and the write pointer will be unaffected. TDTREQ will not be re-asserted until the
Transmit Frame Status has been read.
After a RTRY error, all further packet transmission will
be suspended until the Transmit Frame Status is read,
regardless of whether additional packet data exists in
the FIFO to be transmitted. Receive FIFO read operations are not impaired.
Packets experiencing 16 unsuccessful attempt to
transmit will not be re-tried. Recovery from this condition must be performed by upper layer software.
Abnormal network conditions include:
(a)
Loss of carrier.
(b)
Late collision.
(c)
SQE Test Error.
52
These should not occur on a correctly configured 802.3
network, but will be reported if the network has been
incorrectly configured or a fault condition exists.
(a) A loss of carrier condition will be reported if the
MACE device cannot observe receive activity while it is
transmitting. After the MACE device initiates a transmission it will expect to see data looped-back on the
receive input path. This will internally generate a carrier
sense, indicating that the integrity of the data path to
and from the external MAU is intact, and that the MAU
is operating correctly.
When the AUI port is selected, if carrier sense does not
become active in response to the data transmission, or
becomes inactive before the end of transmission, the
loss of carrier (LCAR) error bit will be set in the Transmit Frame Status (bit 7) after the packet has been
transmitted. The packet will not be re-tried on the basis
of an LCAR error.
When the 10BASE–T port is selected, LCAR will be
reported for every packet transmitted during the Link
fail condition.
When the GPSI port is selected, LCAR will be reported
if the RXCRS input pin fails to become active during a
transmission, or once active, goes inactive before the
end of transmission.
When the DAI port is selected, LCAR errors will not
occur, since the MACE device will internally loop back
the transmit data path to the receiver. The loop back
feature must not be performed by the external transceiver when the DAI port is used.
During internal loopback, LCAR will not be set, since
the MACE device has direct control of the transmit and
receive path integrity. When in external loopback,
LCAR will operate normally according to the specific
port which has been selected.
(b) A late collision will be reported if a collision condition
exists or commences 64 byte times (512 bit times) after
the transmit process was initiated (first bit of preamble
commenced). The MACE device will abandon the
transmit process for the particular frame, complete
transmission of the jam sequence (32-bit all zeroes
pattern), de-assert the TDTREQ pin, report the Late
Collision (LCOL) and Transmit Status Valid (XMTSV) in
the Transmit Frame Status, and set the XMTINT bit in
the Interrupt Register, causing activation of the external
INTR pin providing the interrupt is unmasked.
Once the XMTINT condition has been externally recognized, the Transmit Frame Counter (XMTFC) can be
read to determine whether the tail end of the frame that
suffers the LCOL error is still in the host memory (i.e.,
when XMTFC = 0). This XMTFC read should be
requested before the Transmit Frame Status read
since reading the XMTFS would cause the XMTFC to
decrement. If the tail end of the frame is indeed still in
Am79C940
the host memory, the host is responsible for ensuring
that the tail end of the frame does not get written into
the FIFO and does not get transmitted as a whole
frame. It is recommended that the host clear the tail
end of the frame from the host memory before requesting the XMTFS read so that after the XMTFS
read,when the MACE device re-asserts TDTREQ, the
tail end of the frame does not get written into the FIFO.
The Transmit Frame Status read will indicate that the
LCOL error occurred. The read operation on the Transmit Frame Status will update the FIFO read and write
pointers. If no End-of-Frame write (EOF pin assertion)
had occurred during the FIFO write sequence, the entire transmit path will be reset (which will update the
Transmit FIFO watermark with the current XMTFW
value in the FIFO Configuration Control register). If a
whole frame resides in the FIFO, the read pointer will
be moved to the start of the next frame or free location
in the FIFO, and the write pointer will be unaffected.
TDTREQ will not be re-asserted until the Transmit
Frame Status has been read.
After an LCOL error, all further packet transmission will
be suspended until the Transmit Frame Status is read,
regardless of whether additional packet data exists in
the FIFO to be transmitted. Receive FIFO operations
are unaffected.
Packets experiencing a late collision will not be re-tried.
Recovery from this condition must be performed by
upper layer software.
(c) During the inter packet gap time following the completion of a transmitted message, the AUI CI± pair is
asserted by some transceivers as a self-test. When the
AUI port has been selected, the integral Manchester
Encoder/Decoder will expect the SQE Test Message
(nominal 10 MHz sequence) to be returned via the CI±
pair, within a 40 network bit time period after DI± goes
inactive. If the CI± input is not asserted within the 40
network bit time period following the completion of
transmission, then the MACE device will set the CERR
bit (bit 5) in the Interrupt Register. The INTR pin will be
activated if the corresponding mask bit CERRM = 0.
When the GPSI port is selected, the MACE device will
expect the CLSN input pin to be asserted 40 bit times
after the transmission has completed (after TXEN output pin has gone inactive). When the DAI port has
been selected, the CERR bit will not be reported. A
transceiver connected via the DAI port is not expected
to support the SQE Test Message feature.
Host related transmit exception conditions include:
(a) Overflow caused by excessive writes to the
Transmit FIFO (DTV will not be issued if the Transmit FIFO is full).
(b) Underflow caused by lack of host writes to the
Transmit FIFO.
(c) Not reading current Transmit Frame Status.
(a) The host may continue to write to the Transmit FIFO
after the TDTREQ has been de-asserted, and can
safely do so on the basis of knowledge of the number
of free bytes remaining (set by XMTFW in the FIFO
Configuration Control register). If however the host
system continues to write data to the point that no additional FIFO space exists, the MACE device will not
return the DTV signal and hence will effectively not
acknowledge acceptance of the data. It is the host’s
responsibility to ensure that the data is re-presented at
a future time when space exists in the Transmit FIFO,
and to track the actual data written into the FIFO.
(b) If the host fails to respond to the TDTREQ from the
MACE device before the Transmit FIFO is emptied, a
FIFO underrun will occur. The MACE device will in this
case terminate the network transmission in an orderly
sequence. If less than 512 bits have been transmitted
onto the network the transmission will be terminated
immediately, generating a runt packet. If greater than
512 bits have been transmitted, the message will have
the current CRC inverted and appended at the next
byte boundary, to guarantee an FCS error is detected
at the receiving station. The MACE device will report
this condition to the host by de-asserting the TDTREQ
pin, setting the UFLO and XMTSV bits (in the Transmit
Frame Status) and the XMTINT bit (in the Interrupt
Register), and asserting the INTR pin providing the corresponding XMTINTM bit (in the Interrupt Mask
Regis ter) is cleared.
Once the XMTINT condition has been externally recognized, the Transmit Frame Counter (XMTFC) can be
read to determine whether the tail end of the frame that
suffers the UFLO error is still in the host memory (i.e.,
when XMTFC = 0). In the case of FIFO underrun, this
will definitely be the case and the host is responsible for
ensuring that the tail end of the frame does not get written into the FIFO and does not get transmitted as a
whole frame. It is recommended that the host clear the
tail end of the frame from the host memory before
requesting the XMTFS read so that after the XMTFS
read, when the MACE device re-asserts TDTREQ, the
tail end of the frame does not get written into the FIFO.
The Transmit Frame Status read will indicate that the
UFLO error occurred. The read operation on the Transmit Frame Status will update the FIFO read and write
pointers and the entire transmit path will be reset
(which will update the Transmit FIFO watermark with
the current XMTFW value in the FIFO Configuration
Control register). TDTREQ will not be re-asserted until
the Transmit Frame Status has been read.
(c) The MACE device will internally store the Transmit
Frame Status for up to two packets. If the host fails to
read the Transmit Frame Status and both internal
entries become occupied, the MACE device will not
commence any subsequent transmit frames to prevent
overwriting of the internally stored values. This will
Am79C940
53
occur regardless of the number of bytes written to the
Transmit FIFO.
RECEIVE OPERATION
The receive operation and features of the MACE device are controlled by programmable options. These
options are programmed through the BIU, FIFO and
MAC Configuration Control registers.
Parameters controlled by the MAC Configuration Control register are generally programmed only once, during initialization, and are therefore static during the
normal operation of the MACE device (see the Media
Access Control section for a detailed description). The
features controlled by the FIFO Configuration Control
register and the Receive Frame Control register can be
programmed without performing a reset on the part.
The host is responsible for ensuring that no data is
present in the Receive FIFO when re-programming the
receive attributes.
Receive FIFO Read
The Receive FIFO is accessed by performing a host
generated read sequence on the MACE device. See
the Slave Access Operation-Read Access section and
the AC Waveforms section, Host System Interface, figures: “2 Cycle Receive FIFO/Register Read Timing”
and “3 Cycle Receive FIFO/Register Read Timing” for
details of the read access timing.
Note that EOF will be asserted by the MACE device
during the last data byte/word transfer.
Receive Function Programming
The Receive Frame Control register allows programming of the automatic pad field stripping feature and
the configuration of the Match/Reject (M/R) pin.
ASTRP RCV and M/R must be static when the receive
function is enabled (ENRCV = 1). The receiver should
be disabled before (re-) programming these options.
The EADI port can be used to permit reception of
frames to commence whilst external address decoding
takes place. The M/R bit defines the function of the
EAM/R pin, and hence whether frames will be
accepted or rejected by the external address
comparison logic.
The programming of additional receive attributes are
distributed between the FIFO and MAC Configuration
Control registers, and the User Test Register.
All receive frames can be accepted by setting the
PROM bit (bit 7) in the MAC Configuration Control register. When PROM is set, the MACE device will attempt
to receive all messages, subject to minimum frame
enforcement. Setting PROM will override the use of the
EADI port to force the rejection of unwanted messages.
See the sections External Address Detection Interface
for more details.
54
The point at which RDTREQ is asserted in relation to
the number of bytes of a frame that are present in the
Receive FIFO (RCVFIFO) is controlled by the RCVFW
bits in the FIFO Configuration Control register, or the
LLRCV bit in the Receive Frame Control register.
RDTREQ will be asserted when one of the following
conditions is true:
(i) There are at least 64 bytes in the RCVFIFO.
(ii) The received packet has passed the 64 byte minimum criteria, and the number of bytes in the
RCVFIFO is greater than or equal to the threshold
set by the RCVFW (16 or 32 bytes).
(iii) A receive packet has completed, and part or all of
it is present in the RCVFIFO.
(iv) The LLRCV bit has been set and greater than
12-bytes of at least 8 bytes have been received.
Note that if the RCVFW is set below the 64-byte limit,
the MACE device will still require 64-bytes of data to be
received before the initial assertion of RDTREQ. Subsequently, RDTREQ will be asserted at any time the
RCVFW threshold is exceeded. The only times that the
RDTREQ will be asserted when there are not at least
an initial 64-bytes of data in the RCVFIFO are:
(i) When the ASTRP RCV bit has been set in the Receive Frame Control register, and the pad is automatically stripped from a minimum length packet.
(ii) When the RPA bit has been set in the User Test
Register, and a runt packet of at least 8 bytes has
been received.
(iii) When the LLRCV bit has been set in the Receive
Frame Control register, and at least 12-bytes (after
SFD) has been received.
No preamble/SFD bytes are loaded into the Receive
FIFO. All references to bytes past through the receive
FIFO are received after the preamble/SFD sequence.
Depending on the bus latency of the system, RCVFW
can be set to ensure that the RCVFIFO does not overflow before more data is read. When the entire frame is
in the RCVFIFO, RDTREQ will be asserted regardless
of the value in RCVFW. The default value of RCVFW is
64-bytes after hardware or software reset.
The receive operation of the MACE device can be
halted at any time by clearing the ENRCV bit in the
MAC Configuration Control register. Note that any
receive frame currently in progress will be accepted
normally, and the MACE device will disable the receive
process once the message has completed. The Missed
Packet Count (MPC) will be incremented for
Am79C940
56
Bits
Preamble
1010....1010
8
Bits
SYNCH
10101011
6
Bytes
Dest.
ADDR.
6
Bytes
2
Bytes
SRCE.
ADDR.
Length
46–1500
Bytes
4
Bytes
LLC
DATA
Pad
1–1500
Bytes
45–0
Bytes
FCS
Start of Packet
at Time= 0
Bit
0
Increasing Time
Bit Bit
7 0
Most
Significant
Byte
Bit
7
Least
Significant
Byte
16235D-9
802.3 Packet and Length Field Transmission Order
subsequent packets that would have normally been
passed to the host, and are now ignored due to the
disabled state of the receiver.
field stripped. Receive frames which have a length field
of 46 bytes or greater will be passed to the host
unmodified.
Note that clearing the ENRCV bit disables the assertion of RDTREQ. If ENRCV is cleared during receive
activity and remains cleared for a long time and if the
tail end of the receive frame currently in progress is
Since any valid Ethernet Type field value will always be
greater than a normal 802.3 Length field, the MACE
device will not attempt to strip valid Ethernet frames.
longer than the amount of space available in the
Receive FIFO, Receive FIFO overflow will occur. However, even with RDTREQ deasserted, if there is valid
data in the Receive FIFO to be read, successful slave
reads to the Receive FIFO can be executed (indicated
by valid DTV). It is the host’s responsibility to avoid the
overflow situation.
Note that for some network protocols, the value passed
in the Ethernet Type and/or 802.3 Length field is not
compliant with either standard and may cause
problems.
The diagram below shows the byte/bit ordering of the
received length field for an 802.3 compatible frame
format.
Automatic Pad Stripping
Receive FCS Checking
During reception of a frame, the pad field can be
stripped automatically. ASTRP RCV = 1 enables the
automatic pad stripping feature. The pad field will be
stripped before the frame is passed to the FIFO, thus
Reception and checking of the received FCS is performed automatically by the MACE device. Note that if
the Automatic Pad Stripping feature is enabled,
the received FCS will be verified against the value
computed for the incoming bit stream including pad
characters, but it will not be passed through the Receive FIFO to the host. If an FCS error is detected, this
will be reported by the FCS bit (bit 4) in the Receive
Frame Status.
preserving FIFO space for additional frames. The FCS
field will also be stripped, since it is computed at the
transmitting station based on the data and pad field
characters, and will be invalid for a receive frame that
has the pad characters stripped.
The number of bytes to be stripped is calculated from
the embedded length field (as defined in the IEEE
802.3 definition) contained in the packet. The length
indicates the actual number of LLC data bytes contained in the message. Any received frame which contains a length field less than 46 bytes will have the pad
Receive Status Information
The EOF indication signals that the last byte/word of
data has been passed from the FIFO for the specific
frame. This will be accompanied by a RCVINT indication in the the Interrupt Register signaling that the
Receive Frame Status has been updated, and must be
Am79C940
55
read. The Receive Frame Status is a single location
which must be read four times to allow the four bytes of
status information associated with each frame to be
read. Further data read operations from the Receive
FIFO using the Register Address mode, will be ignored
by the MACE device (indicated by the MACE chip not
returning DTV) until all four bytes of the Receive Frame
Status have been read. Alternatively, the FIFO Direct
access mode may be used to read the Receive Frame
Status through the Receive FIFO. In either case, the
4-byte total must be read before additional receive data
can be read from the Receive FIFO. However, the
RDTREQ indication will continue to reflect the state of
the Receive FIFO as normal, regardless of whether the
Receive Frame Status has been read. DTV will not be
returned when a read operation is performed on the
Receive Frame Status location and no valid status is
present or ready.
Note that the Receive Frame Status can be read using
either the Register Address or FIFO Direct modes. For
additional details, see the section Receive FIFO Read.
Receive Exception Conditions
Exception conditions for frame reception fall into two
distinct categories; those which are the result of normal
network operation, and those which occur due to
abnormal network and/or host related events.
Normal events which may occur and which are handled
autonomously by the MACE device are basically collisions within the slot time and automatic runt packet
deletion. The MACE device will ensure that any receive
packet which experiences a collision within 512 bit
times from the start of reception (excluding preamble)
will be automatically deleted from the Receive FIFO
with no host intervention (the state of the RPA bit in the
User Test Register; or the RCVFW bits in the FIFO
Configuration Control register have no effect on this).
This criteria will be met, regardless of whether the
receive frame was the first (or only) frame in the
Receive FIFO, or if the receive frame was queued
behind a previously received message.
Abnormal network conditions include:
■ FCS errors
■ Framing errors
■ Dribbling bits
■ Late collision
These should not occur on a correctly configured 802.3
network, but may be reported if the network has been
incorrectly configured or a fault condition exists.
Host related receive exception conditions include:
(a)
56
Underflow caused by excessive reads from the
Receive FIFO (DTV will not be issued if the
Receive FIFO is empty)
(b)
Overflow caused by lack of host reads from the
Receive FIFO
(c)
Missed packets due to lack of host reads from
the Receive FIFO and/or the Receive Frame
Status
(a) Successive read operations from the Receive FIFO
after the final byte of data/status has been read, will
cause the DTV pin to remain de-asserted during the
read operation, indicating that no valid data is present.
There will be no adverse effect on the Receive FIFO.
(b) Data present in the Receive FIFO from packets
which completed before the overflow condition
occurred, can be read out by accessing the Receive
FIFO normally. Once this data (and the associated
Receive Frame Status) has been read, the EOF indication will be asserted by the MACE device during the
first read operation takes place from the Receive FIFO,
for the packet which suffered the overflow. If there were
no other packets in the FIFO when the overflow
occurred, the EOF will be asserted on the first read
from the FIFO. In either case, the EOF indication will be
accompanied by assertion of the INTR pin, providing
that the RCVINTM bit in the Interrupt Mask Register is
not set. If the Register Address mode is being used, the
host is required to access the Receive Frame Status
location using four separate read cycles. Further
access to the Receive FIFO will be ignored by the
MACE device until all four bytes of the Receive Frame
Status have been read. DTV will not be returned if a
Receive FIFO read is attempted. If the FIFO Direct
mode is being used, the host can read the Receive
Frame Status through the Receive FIFO, but the host
must be aware that the subsequent four cycles will
yield the receive status bytes, and not data from the
same or a new packet. Only the OFLO bit will be valid
in the Receive Frame Status, other error/status and the
RCVCNT fields are invalid.
While the Receive FIFO is in the overflow condition, it
is deaf to additional receive data on the network. However, the MACE device internal address detect logic
continues to operate and counts the number of packets
that would have been passed to the host under normal
(non overflow) conditions. The Missed Packet Count
(MPC) is an 8-bit count (in register 24) that maintains
the number of packets which pass the address match
criteria, and complete without collision. The MPC
counter will wrap around when the maximum count of
255 is reached, setting the MPCO (Missed Packet
Count Overflow) bit in the Interrupt Register, and
asserting the INTR pin providing that MPCOM (Missed
Packet Count Overflow Mask) in the Interrupt Mask
Register is clear. MPCO will be cleared (the interrupt
will be unmasked) after hardware or software reset.
However, until the first time that the receiver is enabled,
MPC will not increment, hence no interrupt will occur
due to missed packets after a reset.
Am79C940
(c) Failure to read packet data from the Receive FIFO
will eventually cause an overflow condition. The FIFO
will maintain any previously completed packet(s), which
can be read by the host at its convenience. However,
packet data on the network will no longer be received,
regardless of destination address, until the overflow is
cleared by reading the remaining Receive FIFO data
and Receive Status. The MACE device will increment
the Missed Packet Count (MPC) register to indicate that
a packet which would have been normally passed to the
host, was dropped due to the error condition.
Note: The moment a packet overflow is detected or
read, an EOF with INT is generated. On status read
(OFLOW), the FIFO pointers are reset to the first
location. This essentially flushes the FIFO.
LOOPBACK OPERATION
During loopback, the FCS logic can be allocated to the
receiver by setting RCVFCSE = 1 in User Test Register. This permits both the transmit and receive FCS operations to be verified during the loopback process.
The state of RCVFCSE is only valid during loopback
opera tion.
If RCVFCSE = 0, the MACE device will calculate and
append the FCS to the transmitted message. The
receive message passed to the host will therefore contain an additional four bytes of FCS. The Receive
Frame Status will indicate the result of the loopback
operation and the RCVCNT.
If RCVFCSE = 1, the last four bytes of the transmit
message must contain the FCS computed for the
transmit data preceding it. The MACE device will transmit the data without addition of an FCS field, and the
FCS will be calculated and verified at the receiver.
The loopback facilities of the MACE device allow full
operation to be verified without disturbance to the network. Loopback operation is also affected by the state
of the Loopback Control bits (LOOP [0–1]) in the User
Test Register. This affects whether the internal MENDEC is considered part of the internal or external
loop-back path.
When in the loopback mode(s), the multicast address
detection feature of the MACE device, programmed by
the contents of the Logical Address Filter (LADR [63–
0]) can only be tested when RCVFCSE = 1, allocating
the CRC generator to the receiver. All other features
operate identically in loopback as in normal operation,
such as automatic transmit padding and receivepad
stripping.
USER ACCESSIBLE REGISTERS
The following registers are provided for operation of the
MACE device. All registers are 8-bits wide unless
otherwise stated. Note that all reserved register bits
should be written as zero.
Receive FIFO (RCVFIFO)
(REG ADDR 0)
RCVFIFO [15–0]
This register provides a 16-bit data path from the
Receive FIFO. Reading this register will read one word/
byte from the Receive FIFO. The RCVFIFO should
only be read when Receive Data Transfer Request
(RDTREQ) is asserted. If the RCVFIFO location is read
before 64-bytes are available in the RCVFIFO (or
12-bytes in the case that LLRCV is set in the Receive
Frame Control register), DTV will not be returned.
Once the 64-byte threshold has been achieved and
RDTREQ is asserted, the de-assertion of RDTREQ
does not prevent additional data from being read from
the RCVFIFO, but indicates the number of additional
bytes which are present, before the RCVFIFO is emptied, and subsequent reads will not return DTV (see
the FIFO Sub-System section for additional details).
Write operations to this register will be ignored and
DTV will not be returned.
Byte transfers from the RCVFIFO are supported, and
will be fully aligned to the target memory architecture,
defined by the BSWP bit in the BIU Configuration Control register. The Byte Enable inputs (BE1-0) will define
which half of the data bus should be used for the transfer. The external host/controller will be informed that
the last byte/word of data in a receive frame is being
read from the RCVFIFO, when the MACE device asserts the EOF signal.
Transmit FIFO (XMTFIFO)
(REG ADDR 1)
XMTFIFO [15–0]
This register provides a 16-bit data path to the Transmit
FIFO. Byte/word data written to this register will be
placed in the Transmit FIFO. The XMTFIFO can be
written at any time the Transmit Data Transfer Request
(TDTREQ) is asserted. The de-assertion of TDTREQ
does not prevent data being written to the XMTFIFO,
but indicates the number of additional write cycles
which can take place, before the XMTFIFO is filled, and
subsequent writes will not return DTV (see the FIFO
Sub-System section for additional details). Read operations to this register will be ignored and DTV will not
be returned.
Byte transfers to the XMTFIFO are supported, and
accept data from the source memory architecture to
ensure the correct byte ordering for transmission,
defined by the BSWP bit in the MAC Configuration
Control register. The Byte Enable inputs (BE1-0) will
define which half of the data bus should be used for the
transfer. The use of byte transfers have implications on
the latency time provided by the XMTFIFO (see the
FIFO Sub-System section for additional details). The
external host/controller must indicate the last byte/word
Am79C940
57
of data in a transmit frame is being written to the
XMTFIFO, by asserting the EOF signal.
Transmit Frame Control (XMTFC)
(REG ADDR 2)
The Transmit Frame Control register is latched internally on the last write to the Transmit FIFO for each individual packet, when EOF is asserted. This permits
automatic transmit padding and FCS generation on a
packet-by-packet basis.
DRTRY
Bit
Bit 7
Bit 6-4
Bit 3
58
RES
RES
Name
DRTRY
DXMTFCS
RES
RES
APAD XMT
Description
Disable Retry. When DRTRY is
set, the MACE device will provide a single transmission attempt for the packet, all further
retries will be suspended. In the
case of a collision during the attempt, a Retry Error (RTRY) will
be reported in the Transmit Status. With DRTRY cleared, the
MACE device will attempt up to
15 retries (16 attempts total) before indicating a Retry Error.
DRTRY is cleared by activation
of the RESET pin or SWRST bit.
DRTRY is sampled during the
transmit process when a
collision occurs. DRTRY should
not be changed whilst data
remains in the Transmit FIFO
since this may cause an unpredictable retry response to a collision. Once the Transmit FIFO is
empty, DRTRY can be reprogrammed.
RES
Reserved. Read as zeroes.
Always write as zeroes.
DXMTFCS Disable Transmit FCS. When
DXMTFCS = 0 the transmitter
will generate and append an
FCS to the transmitted frame.
When DXMTFCS = 1, no FCS
will be appended to the transmitted frame, providing that APAD
XMT is also clear. If APAD XMT
is set, the calculated FCS will be
appended to the transmitted
message regardless of the state
of DXMTFCS. The value of
DXMTFCS for each frame is
programmed when EOF is asserted to transfer the last byte/
word for the transmit packet to
the FIFO. DXMTFCS is cleared
by activation of the RESET pin
or SWRST bit. DXMTFCS is
sampled only when EOF is
asserted during a Transmit FIFO
write.
Bit
Bit 2-1
Name
Description
RES
Reserved. Read as zeroes.
Always write as zeroes.
Bit 0
APAD XMT Auto Pad Transmit. APAD XMT
enables the automatic padding
feature. Transmit frames will be
padded to extend them to 64
bytes including FCS. The FCS is
calculated for the entire frame
including pad, and appended after the pad field. APAD XMT will
override the programming of the
DXMTFCS bit. APAD XMT is set
by activation of the RESET pin
or SWRST bit. APAD XMT is
sampled only when EOF is asserted during a Transmit FIFO
write.
Transmit Frame Status (XMTFS)
(REG ADDR 3)
The Transmit Frame Status is valid when the XMTSV
bit is set. The register is read only, and is cleared when
XMTSV is set and a read operation is performed. The
XMTINT bit in the Interrupt Register will be set when
any bit is set in this register.
Note that if XMTSV is not set, the values in this register
can change at any time, including during a read operation. This register should be read after the Transmit
Retry Count (XMTRC). See the description of the
Transmit Retry Count (XMTRC) for additional details.
XMTSV
Bit
UFLO
LCOL MORE
Name
Bit 7
XMTSV
Bit 6
UFLO
Bit 5
LCOL
Am79C940
ONE
DEFER
LCAR
RTRY
Description
Transmit Status Valid. Transmit
Status Valid indicates that this
status is valid for the last frame
transmitted. The value of
XMTSV will not change during a
read operation.
Underflow. Indicates that the
Transmit FIFO emptied before
the end of frame was reached.
The transmitted frame is truncated at that point. If UFLO is set,
TDTREQ will be de-asserted,
and will not be re-asserted until
the XMTFS has been read.
Late Collision. Indicates that a
collision occurred after the slot
time of the channel elapsed. If
LCOL is set, TDTREQ will be
de-asserted, and will not be
re-asserted until the XMTFS has
been read. The MACE device
does not retry after a late
collision.
Bit 4
MORE
More. Indicates that more than
one retry was needed to transmit
the frame. ONE, MORE and
RTRY are mutually exclusive.
Bit 3
ONE
One. Indicates that exactly one
retry was needed to transmit the
frame. ONE, MORE and RTRY
are mutually exclusive.
Bit 2
DEFER
Defer. Indicates that MACE
device had to defer transmission
of the frame. This condition
results if the channel is busy
when the MACE device is ready
to transmit.
Bit 1
LCAR
Loss of Carrier. Indicates that
the carrier became false during
a transmission. The MACE
device does not retry upon Loss
of Carrier. LCAR will not be set
when the DAI port is selected,
when the 10BASE-T port is selected and in the link pass state,
or during any internal loopback
mode. When the 10BASE-T port
is selected and in the link fail
state, LCAR will will be reported
for any transmission attempt.
Bit 0
RTRY
Retry Error. Indicates that all
attempts to transmit the frame
were unsuccessful, and that further attempts have been aborted. If Disable Retry (DRTRY in
the Transmit Frame Control register) is cleared, RTRY will be
set when a total of 16 unsuccessful attempts were made to
transmit the frame. If DRTRY is
set, RTRY indicates that the first
and only attempt to transmit the
frame was unsuccessful. ONE,
MORE and RTRY are mutually
exclusive. If RTRY is set,
TDTREQ will be de-asserted,
and will not be re-asserted until
the XMTFS has been read.
Transmit Retry Count (XMTRC)
(REG ADDR 4)
Bit
Bit 3-0
RES
RES
RES
Description
EXDEF
Excessive Defer. The EXDEF bit
will be set if a transmit frame
waited for an excessive period
for transmission. An excessive
defer time is defined in accordance with the following (from
page 34, section 5.2.4.1 of IEEE
Std 802.3h-1990 Layer Management):maxDeferTime = {2 x
(max frame size x 8)} bits where
maxFrameSize = 1518 bytes
(from page 68, section 4.4.2.1 of
ANSI/IEEE Std 802.3-1990).
So, the maxDeferTime = 24288
bits = 214+ 212 + 211+ 210 + 29
+27 +26 +25
Bit 6-4 RES
Reserved. Read as zeroes.
Always write as zeroes.
Bit 3-0
XMTRCTransmit Retry Count.
Contains
[3-0]
the count of the number of retry
attempts made by the MACE
device to transmit the current
transmit packet. The value of the
counter will be zero if the first
transmission attempt was successful, and a maximum of 15 if
all retry attempts were utilized.
RTRY will be set in Transmit
Frame Status if all 16 attempts
were unsuccessful.
Receive Frame Control (RCVFC) (REG ADDR 5)
RES
RES
Bit
RES
Name
Bit 7-4
RES
Bit 3
LLRCV
The Transmit Retry Count should be read only in
response to a hardware interrupt request (INTR
asserted) when XMTINT is set in the Interrupt Register,
or after XMTSV is set in the Poll Register.The register
should be read before the Transmit Frame Status
register. Reading the Transmit Frame Status with
XMTSV set will cause the XMTRC value to be reset.
This register is read only.
EXDEF
Name
XMTRC[3-0]
Am79C940
RES
LLRCV
M/R
RES
ASTRPRCV
Description
Reserved. Read as zeroes.
Always write as zeroes.
Low Latency Receive. A
programmable option to allow
access to the Receive FIFO
before the 64-byte threshold has
been reached. When set, data
can be read from the RCVFIFO
once a low threshold (12-bytes
after SFD plus synchronization)
has been exceeded, causing
RDTREQ to be asserted.
RDTREQ will remain asserted
as long as one read cycle can be
performed on the RCVFIFO
(identical to the burst mode).
Indication of a valid read cycle
from the RCVFIFO will return
DTV asserted. Reading the
RCVFIFO before data is available, or while waiting for addi59
Bit 2
Bit 1
M/R
RES
tional data once a packet is in
progress will not cause the
RCVFIFO to underflow, and will
be indicated by DTV being
invalid. The MACE device will no
longer be able to reject runts in
this mode, this responsibility is
transferred to the host system.
In the case of a collided packet
(normal slot time collision or late
collision), the MACE device will
abort the reception, and return
the RCVFS. Note that all collisions in this mode will appear as
late collisions and be reported
by the CLSN bit in the Receive
Status (RCVSTS) byte.
If the host does not keep up with
the incoming receive data, normal RCVFIFO overflow recovery
is provided.
Match/Reject. The Match/Reject
option sets the criteria for the
External Address Detection
Interface. If set, the EAM/R pin is
configured as External Address
Match, and is used to signal the
acceptance of a receive frame to
the MACE device. If cleared, the
pin functions as External
Address Reject and is used to
flush unwanted packets from the
Receive FIFO prior to the first
assertion of RDTREQ. M/R is
cleared by activation of the
RESET pin or SWRST bit. When
the EADI feature is disabled, the
EAM/R pin must be tied active
(low) and all normal receive address recognition configurations
are supported (physical, logical
and promiscuous). See the section “External Address Detection
Interface” for additional details.
Reserved. Read as zero. Always
write as zero. Bit 0 ASTRP RCV
Auto Strip Receive. ASTRP
RCV enables the automatic pad
stripping feature. The pad and
FCS fields will be stripped from
receive frames and not placed in
the FIFO. ASTRP RCV is set by
activation of the RESET pin or
the SWRST bit.
Receive Frame Status (RCVFS)
(REG ADDR 6)
RCVFS [31–00]
In Register Direct mode, access to the Receive FIFO
will be denied until all four status bytes for the completed frame have been read from the Receive Frame
Status location. In FIFO Direct mode, the Receive
Frame Status is read through the Receive FIFO location, by continuing to execute four read cycles after the
completion of packet data (and assertion of EOF). The
Receive Frame Status can be read using either mode,
or a combination of both modes, however each status
byte will be presented only once regardless of access
method. Other register reads and/or writes can be
interleaved at any time, during the Receive Frame
Sta tus sequence.
The Receive Frame Status consists of the following
four bytes of information:
RFS0
RFS1
RFS2
RFS3
Receive Message Byte Count
(RCVCNT) [11–0]
Receive Status, (RCVSTS) [15–12]
Runt Packet Count (RNTPC) [7–0]
Receive Collision Count (RCVCC) [7–0]
RFS0—Receive Message Byte Count (RCVCNT)
RCVCNT [7:0]
Bit
Bit 7-0
Name
RCVCNT
[7:0]
Description
The Receive Message Byte
Count indicates the number of
whole bytes in the received message. If pad bytes were stripped
from the received frame,
RCVCNT indicates the number
of bytes received less the number of pad bytes and less the
number of FCS bytes. RCVCNT
is 12 bits long. If a late collision
is detected (CLSN set in
RCVSTS), the count is an indication of the length (in byte
times) of the duration of the receive activity including the collision. RCVCNT [10:8] correspond to bits 3-0 in RFS1 of the
Receive
Frame
Status.
RCVCNT [11–0] will be invalid
when OFLO is set.
RFS1—Receive Status (RCVSTS)
OFLO CLSN FRAM FCS
Bit
The Receive Frame Status is a single byte location
which must be read by four read cycles to obtain the
four bytes (32-bits) of status associated with each
60
receive frame. Receive Frame Status can be read
using either the Register Direct or FIFO Direct access
modes.
Bit 7
Am79C940
Name
OFLO
RCVCNT [10:8]
Description
Overflow flag. Indicates that the
Receive FIFO over flowed due
Bit 6
Bit 5
Bit 4
Bit 3-0
CLSN
FRAM
FCS
RCVCNT
[11:8]
to the inability of the host/controller to read data fast enough
to keep pace with the receive serial bit stream and the latency
provided by the Receive FIFO itself. OFLO is indicated on the receive frame that caused the
overflow condition; complete
frames in the Receive FIFO are
not affected. While the Receive
FIFO is in the overflow condition,
it ignores additional receive data
on the network. The internal address detect logic will continue
to operate and the Missed Packet Count (MPC in register 24) will
be incremented for each packet
which passes the address match
criteria, and complete without
collision.
Collision Flag. Indicates that the
receive operation suffered a collision during reception of the
frame. If CLSN is set, it indicates
that the receive frame suffered a
late collision, since a frame experiencing collision within the
slot time will be automatically
deleted from the RCVFIFO (providing LLRCV in the Receive
Frame Control register is
cleared). Note that if the LLRCV
bit is enabled, the late collision
threshold is effectively moved
from the normal 64–byte (512–
bit) level to the 12-byte (96–bit)
level. Runt packets suffering a
collision will be flushed from the
RCVFIFO regardless of the
state of the RPA bit (User Test
Register). CLSN will not be set if
OFLO is set.
Framing Error flag. Indicates
that
the
received
frame
contained a non-integer multiple
of bytes and an FCS error. If
there was no FCS error then
FRAM will not be set. FRAM is
not
valid
during
internal
loopback. FRAM will not be set if
OFLO is set.
FCS Error flag. Indicates that
there is an FCS error in the
frame. The receive FCS is
computed and checked normally
when ASTRP RCV = 1, but is not
passed to the host. FCS will not
be set if OFLO is set.
The Receive Message Byte
Count indicates the number of
whole bytes in the received
message from the network.
RCVCNT is 12 bits long, and
valid (accurate) only when there
are no errors reported in the
Receive Status (RCVSTS). If a
late collision is detected (CLSN
set in RCVSTS), the count is an
indication of the length (in byte
times) of the duration of the
receive activity including the
collision. RCVCNT [7:0] correspond to bits 7-0 in RFS0 of the
Receive
Frame
Status.
RCVCNT [11–0} will be invalid
when OFLO is set.
RFS2—Runt Packet Count (RNTPC)
RNTPC [7–0]
Bit
Bit 7-0
Name
Description
RNTPC
The
Runt
Packet
Count
indicates
[7–0]
the number of runt packets
received, addressed to this
node, since the last successfully
received packet. The value does
not roll over after 255 runt
packets have been detected,
and will remain frozen at the
maximum count.
RFS3—Receive Collision Count (RCVCC)
RCVCC [7–0]
Bit
Name
Description
Bit 7–0 RCVCC
[7–0]
The Receive Collision Count indicates the number of collisions
detected on the network since
the last successfully received
packet. The value does not roll
over after 255 collisions have
been detected, and will remain
frozen at the maximum count.
FIFO Frame Count (FIFOFC)
(REG ADDR 7)
RCVFC[3–0]
Bit
Name
Bit 7–4 RCVFC
Am79C940
[3–0]
XMTFC[3–0]
Description
Receive Frame Count. The
(read
only) count of the frames in the
Receive FIFO. A frame is counted when the last byte is put in
the FIFO. The counter is decremented when the last byte of the
frame is read. If the RCVFC
reaches its maximum value of
61
15, additional receive frames will
be ignored, and the Missed
Packet Count (MPC) register will
be incremented for frames which
match the internal address(es)
of the MACE device.
Bit 3–0 XMTFC
Transmit Frame Count. The
[3–0]
(read only) count of the frames in
the Transmit FIFO. A frame is
counted when the last byte is put
in the FIFO. The counter is decremented when XMTSV (in the
Transmit Frame Status and Poll
Register) is set and the Transmit
Frame Status read access is
performed.
Interrupt Register (IR)
(REG ADDR 8)
All status bits are set upon occurrence of an event and
cleared when read. The resister is read only. In addition
all status bits are cleared by hardware or software
reset. Bit assignments for the register are as follows:
JAB
Bit
Bit 7
Bit 6
62
BABL CERR
Name
JAB
BABL
RDVCCO
RNTPCO MPCO RCVINT
Bit 5
CERR
Bit 4
RCVCCO
XMTINT
Description
Jabber Error. JAB indicates that
the MACE device attempted to
transmit for an excessive time
period (20–150 ms), when using
either the DAI port or the
10BASE–T port. If the internal
jabber timer expires during
transmission, the transmit bit
stream will be interrupted, until
the internal transmission ceases
and the unjab timer (0.5 s ±0.25
s) expires. The jabber function
will be disabled, and JAB will not
be set, regardless of transmission length, when either the AUI
or GPSI ports have been
selected.
JAB is READ/CLEAR only, and
is set by the MACE device and
reset when read. Writing has no
effect. It is also cleared by activation of the RESET pin or
SWRST bit.
Babble Error. BABL is the
transmitter time-out error. It indicates that the transmitter has
been on the channel longer
than the time required to send
the maximum packet. It will be
set after 1519 bytes (or greater) have been transmitted. The
MACE device will continue to
transmit until the current packet transmission is over. The
INTR pin will be activated if the
Am79C940
corresponding
mask
bit
BABLM = 0.
BABL is READ/CLEAR only,
and is set by the MACE device
and reset when read. Writing
has no effect. It is also cleared
by activation of the RESET pin
or SWRST bit.
Collision Error. CERR indicates
the absence of the Signal Quality Error Test (SQE Test) message after a packet transmission. The SQE Test message is
a transceiver test feature. Detection depends on the MACE network interface selected. In all
cases, CERR will be set if the
MACE device failed to observe
the SQE Test message within 20
network bit times after the packet transmission ended. When
CERR is set, the INTR pin will be
activated if the corresponding
mask bit CERRM = 0.
When the AUI port is selected,
the SQE Test message is
returned over the CI± pair as a
brief (5-15 bit times) burst of 10
MHz
activity.
When
the
10BASE–T port is selected,
CERR will be reported after a
transmission only when the
internal transceiver is in the link
fail state (LNKST pin = HIGH).
When the GPSI port is selected,
the CLSN pin must be asserted
by the external encoder/decoder
to provide the SQE Test function. When the DAI port is selected, CERR will not be reported at
any time.
CERR is READ/CLEAR only. It
is set by the MACE and reset
when read. Writing has no
effect. It is also cleared by
activation of the RESET pin or
SWRST bit.
Receive Collision Count Overflow. Indicates that the Receive
Collision Count register rolled
over at a value of 255 receive
collisions. Receive collisions are
defined as received frames
which suffered a collision. The
INTR pin will be activated if the
corresponding mask bit RCVCCOM = 0. Note that the RCVCC
value returned in the Receive
Frame Status (RFS3) will freeze
at a value of 255, whereas this
register based version of
Bit 3
Bit 2
Bit 1
RNTPCO
MPCO
RCVINT
RCVCC (REG ADDR 27) is free
running.
RCVCCO is READ/CLEAR only.
It is set by the MACE device and
reset when read. Writing has no
effect. It is also cleared by
asserting the RESET pin or
SWRST bit.
Runt Packet Count Overflow.
Indicates that the Runt Packet
Count register rolled over at a
value of 255 runt packets. Runt
packets are defined as received
frames which passed the internal address match criteria but
did not contain a minimum of
64-bytes of data after SFD. The
INTR pin will be activated if
the corresponding mask bit
RNTPCOM = 0. Note that the
RNTPC value returned in the
Receive Frame Status (RFS2)
will freeze at a value of 255,
whereas this register based
version of RNTPC (REG ADDR
26) is free running.
RNTPCO is READ/CLEAR only.
It is set by the MACE device and
reset when read. Writing has no
effect. It is also cleared by
asserting the RESET pin or
SWRST bit.
Missed Packet Count Overflow.
Indicates that the Missed Packet
Count register rolled over at a
value of 255 missed frames.
Missed frames are defined as
received frames which passed
the internal address match
criteria but were missed due to a
Receive FIFO overflow, the
receiver being disabled (ENRCV
= 0) or an excessive receive
frame count (RCVFC > 15). The
INTR pin will be activated if the
corresponding mask bit MPCOM
= 0.
MPCO is READ/CLEAR only. It
is set by the MACE device and
reset when read. Writing has no
effect. It is also cleared by
asserting the RESET pin or
SWRST bit.
Receive Interrupt. Indicates that
the host read the last byte/word
of a packet from the Receive
FIFO. The Receive Frame Status is available immediately on
the next host read operation.
The INTR pin will be activated if
the corresponding mask bit
RCVINTM = 0.
RCVINT is READ/CLEAR only.
It is set by the MACE device and
reset when read. Writing has no
effect. It is also cleared by activation of the RESET pin or
SWRST bit.
Bit 0
XMTINT
Transmit Interrupt. Indicates that
the MACE device has completed
the transmission of a packet and
updated the Transmit Frame
Status. The INTR pin will be
activated if the corresponding
mask bit XMTINTM = 0.
XMTINT is READ/CLEAR only.
It is set by the MACE device and
reset when read. Writing has no
effect. It is also cleared by activation of the RESET pin or
SWRST bit.
Interrupt Mask Register (IMR)
(REG ADDR 9)
This register contains the mask bits for the interrupts.
Read/write operations are permitted. Writing a one into
a bit will mask the corresponding interrupt. Writing a
zero to any previously set bit will unmask the corresponding interrupt. Bit assignments for the register are
as follows:
RES
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Am79C940
BABLM
CERRM
Name
RCVCCOM
RNTPCOM
MPCOM
RCVINTM
XMTINTM
Description
JABM
Jabber Error Mask. JABM is the
mask for JAB. The INTR pin will
not be asserted by the MACE
device regardless of the state of
the JAB bit, if JABM is set. It is
cleared by activation of the
RESET pin or SWRST bit.
BABLM
Babble Error Mask. BABLM is
the mask for BABL. The INTR
pin will not be asserted by the
MACE device regardless of the
state of the BABL bit, if BABLM
is set. It is cleared by activation
of the RESET pin or SWRST bit.
CERRM
Collision Error Mask. CERRM is
the mask for CERR. The INTR
pin will not be asserted by the
MACE device regardless of the
state of the CERR bit, if CERRM
is set. It is cleared by activation
of the RESET pin or SWRST bit.
RCVCCOM Receive Collision Count Overflow Mask. RCVCCOM is the
mask for RCVCCO(Receive
Collision Count Overflow). The
INTR pin will not be asserted by
63
Bit 3
Bit 2
Bit 1
Bit 0
the MACE device regardless of
the state of the RCVCCO bit, if
RCVCCOM is set. It is cleared
by activation of the RESET pin
or SWRST bit.
RNTPCOM Runt Packet Count Overflow
Mask. RNTPCOM is the mask
for RNTPCO (Runt Packet
Count Overflow). The INTR pin
will not be asserted by the
MACE device regardless of the
state of the RNTPCO bit, if
RNTPCOM is set. It is cleared by
activation of the RESET pin or
SWRST bit.
MPCOM
Missed Packet Count Overflow
Mask. MPCOM is the mask for
MPCO (Missed Packet Count
Overflow). The INTR pin will not
be asserted by the MACE device
regardless of the state of the
MPCO bit, if MPCOM is set. It is
cleared by activation of the
RESET pin or SWRST bit.
RCVINTM Receive
Interrupt
Mask.
RCVINTM is the mask for
RCVINT. The INTR pin will not
be asserted by the MACE device
regardless of the state of the
RCVINT bit, if RCVINTM is set. It
is cleared by activation of the
RESET pin or SWRST bit.
XMTINTM Transmit
Interrupt
Mask.
XMTINTM is the mask for
XMTINT. The INTR pin will not
be asserted by the MACE device
regardless of the state of the
XMTINT bit, if XMTINT is set. It
is cleared by activation of the
RESET pin or SWRST bit
Bit 6
Transmit
Data
Transfer
Request. An internal indication
of the current request status of
the Transmit FIFO. TDTREQ is
set when the external TDTREQ
signal is asserted.
Bit 5
RDTREQ
Receive Data Transfer Request.
An internal indication of the current request status of the
Receive FIFO. RDTREQ is set
when the external RDTREQ
signal is asserted.
Bit 4-0 RES
Reserved. Read as zeroes.
Always write as zeroes.
BIUConfigurationControl(BIUCC) (REGADDR11)
All bits within the BIU Configuration Control register will
be set to their default state upon a hardware or software reset. Bit assignments are as follows:
RES
Bit
TDTREQ
RDTREQ
RES
RES
Poll Register (PR)
RES
RES
Bit 7
64
Name
XMTSV
Name
RES
Bit 6
BSWP
Bit 5-4
XMTSP
[1-0]
RES
(REG ADDR 10)
This register contains copies of internal status bits to
simplify a host implementation which is non-interrupt
driven. The register is read only, and its status is unaffected by read operations. All register bits are cleared
by hardware or software reset. Bit assignments are as
follows:
Bit
BSWP XMTSP [1-0]
Bit 7
.
XMTSV
TDTREQ
Description
Transmit Status Valid. Transmit
Status Valid indicates that the
Transmit Frame Status is valid.
Am79C940
RES
RES
RES
SWRST
Description
Reserved. Read as zero. Always
write as zero.
Byte Swap. The BSWP function
allows data to and from the
FIFOs to be orientated according to little endian or big endian
byte
ordering
conventions.
BSWP is cleared by by activation of the RESET pin or SWRST
bit, defaulting to Intel byte
ordering.
Transmit Start Point. XMTSP
controls the point preamble
transmission commences in
relation to the number of bytes
written to the XMTFIFO. When
the entire frame is in the XMTFIFO (or the XMTFIFO becomes
full before the threshold is
achieved), transmission of preamble will start regardless of the
value in XMTSP (once the IPG
time has expired). XMTSP is
given a value of 10 (64 bytes)
after hardware or software reset.
Regardless of XMTSP, the FIFO
will not internally over write its
data until at least 64 bytes, or the
entire frame, has been transmitted onto the network. This
ensures that for collisions within
the slot time window, transmit
data need not be re-written to
the XMTFIFO, and re-tries will
be handled autonomously by the
MACE device.
Transmit Start Point
Bit 3-1
XMTSP [1-0]
Bytes
00
4
01
16
10
64
11
112
Reserved. Read as zeroes. Always write as zeroes.
Bit 0
SWRST
Software Reset. When set, provides an equivalent of the hardware RESET pin function. All
register bits will be set to their
default values. The MACE device will require re-initialization
after SWRST has been activated. The MACE device will clear
SWRST during its internal reset
sequence.
FIFO Configuration Control
(REG ADDR 12)
(FIFOCC)
write cycles (including an
End-Of-Frame
delimiter),
TDTREQ may go inactive before
the XMTSP threshold is reached
when using the non burst mode
(XMTBRST = 0). The host must
be aware that despite TDTREQ
going inactive, additional space
exists in the XMTFIFO, and the
data write must continue to
ensure the XMTSP threshold is
achieved. No transmit activity
will commence until the XMTSP
threshold is reached. When
using the burst mode, TDTREQ
will not be de-asserted until only
a single write cycle can be performed. See the FIFO Sub-system section for additional details.
RES
Bit 5-4
RCVFW
[1-0]
All bits within the FIFO Configuration Control register
will be set to their default state upon a hardware or software reset. Bit assignments are as follows:
XMTFW[1-0]
Bit
Bit 7-6
RCVFW [1-0] XMTFWU RCVFWU
Name
XMTBRST
RCVBRST
Description
XMTFW
Transmit
FIFO Watermark.
[1-0]
XMTFW controls the point
TDTREQ is asserted in relation
to the number of write cycles to
the Transmit FIFO. TDTREQ will
be asserted at any time that the
number of write cycles specified
by XMTFW can be executed.
XMTFW is set to a value of 00 (8
cycles) after hardware or
software reset.
Transmit FIFO Watermarks
Receive FIFO Watermark.
RCVFW controls the point
RDTREQ is asserted in relation
to the number of bytes available
in the RCVFIFO. RCVFW specifies the number of bytes which
must be present (once the packet has been verified as a
non-runt), before the RDTREQ
is asserted. Note however that in
order for RDTREQ to be activated for a new frame, at least
64-bytes must have been
received. This effectively avoids
reacting to receive frames which
are runts or suffer a collision during the slot time (512 bit times).
If the Runt Packet Accept feature (RPA in Receive Frame
Control)
is
enabled,
the
RDTREQ pin will be activated as
soon as either 64-bytes are
received, or a complete valid
receive frame is detected
(regardless of length). RCVFW
is set to a value of 10 (64 bytes)
after hardware or software reset.
Receive FIFO Watermarks
XMTSP [1–0]
Bytes
00
8
XMTSP [1–0]
Bytes
01
16
00
16
10
32
01
32
11
XX
10
64
11
XX
The XMTFW value will only be
updated when the XMTFWU bit
is set.
To ensure that sufficient space
is present in the XMTFIFO to
accept the specified number of
Bit 3
Am79C940
XMTFWU
The RCVFW value will only be
updated when the RCVFWU bit
is set.
Transmit
FIFO
Watermark
Update. Allows update of the
65
Bit 2
Bit 1
66
Transmit FIFO Watermark bits.
The XMTFW can be written at
any point, and will be read back
as written. However, the new
value in the XMTFW bits will be
ignored until XMTFWU is set (or
the transmit path is reset due to
a retry failure). The recommended procedure to change the
XMTFW is to write the new value
with XMTFWU set, in a single
write cycle. The XMTFIFO
should be empty and all transmit
activity complete before attempting a watermark update, since
the XMTFIFO will be reset to
allow the new pointer values to
be loaded. It is recommended
that the transmitter be disabled
by clearing the ENXMT bit.
XMTFWU will be cleared by the
MACE device after the new
XMTFW value has been loaded,
or by activation of the RESET
pin or SWRST bit.
RCVFWU Receive
FIFO
Watermark
Update. Allows update of the
Receive FIFO Watermark bits.
The RCVFW bits can be written
at any point, and will read back
as written. However, the new
value in the RCVFW bits will be
ignored until RCVFWU is set.
The recommended procedure to
change the RCVFW is to write
the new value with RCVFWU
set, in a single write cycle. The
RCVFIFO should be empty
before attempting a watermark
update, since the RCVFIFO will
be reset to allow the new pointer
values to be loaded. It is recommended that the receiver be disabled by clearing the ENRCV
bit. RCVFWU will be cleared by
the MACE device after the new
RCVFW value has been loaded,
or by activation of the RESET
pin or SWRST bit.
XMTBRST Transmit Burst. When set, the
transmit burst mode is selected.
The behavior of the Transmit
FIFO high watermark, and
hence the de-assertion of
TDTREQ, will be modified.
TDTREQ will be deasserted if
there are only two bytes of space
available in the XMTFIFO (so
that a full word write can still
occur) or if four bytes of space
exist and the EOF pin is asserted by the host.TDTREQ will be
asserted identically in both
normal and burst modes, when
there is sufficient space in the
XMTFIFO to allow the specified
number of write cycles to occur
(programmed by the XMTFW
bits).
Cleared by activation of the
RESET pin or SWRST bit.
Bit 0
RCVBRST Receive Burst. When set, the
receive burst mode is selected.
The behavior of the Receive
FIFO low watermark, and hence
the de-assertion of RDTREQ,
will be modified. RDTREQ will
de-assert when there are only
2-bytes of data available in the
RCVFIFO (so that a full word
read can still occur).
RDTREQ will be asserted identically in both normal and burst
modes, when a minimum of
64-bytes have been received for
a new frame (or a runt packet
has been received and RPA is
set). Once the 64-byte limit has
been exceeded, RDTREQ will
be asserted providing there is
sufficient data in the RCVFIFO
to exceed the threshold, as programmed by the RCVFW bits.
Cleared by activation of the
RESET pin or SWRST bit.
MAC Configuration
Control (MACCC)
(REG ADDR 13)
This register programs the transmit and receive operation and behavior of the internal MAC engine. All bits
within the MAC Configuration Control register are
cleared upon hardware or software reset. Bit
assignments are as follows:
PROM
Bit
Bit 7
Bit 6
Bit 5
Am79C940
DXMT2PD EMBA RES
Name
PROM
DRCVPA
DRCVBC
ENXMT
ENRCV
Description
Promiscuous. When PROM is
set all incoming frames are
received regardless of the destination address. PROM is
cleared by activation of the
RESET pin or SWRST bit.
DXMT2PD Disable Transmit Two Part
Deferral. When set, disables the
transmit two part deferral option.
DXMT2PD is cleared by
activation of the RESET pin or
SWRST bit.
EMBA
Enable Modified Back-off Algorithm. When set, enables the
Bit 4
RES
Bit 3
DRCVPA
Bit 2
DRCVBC
Bit 1
Bit 0
ENXMT
ENRCV
modified backoff algorithm.
EMBA is cleared by activation of
the RESET pin or SWRST bit.
Reserved. Read as zeroes.
Always write as zeroes.
Disable
Receive
Physical
Address. When set, the physical
address detection (Station or
node ID) of the MACE device will
be disabled. Packets addressed
to the nodes individual physical
address will not be recognized
(although the packet may be
accepted by the EADI mechanism). DRCVPA is cleared by
activation of the RESET pin or
SWRST bit.
Disable Receive Broadcast.
When set, disables the MACE
device from responding to
broadcast messages. Used for
protocols that do not support
broadcast addressing, except as
a function of multicast. DRCVBC
is cleared by activation of the
RESET pin or SWRST bit
(broadcast messages will be
received).
Enable
Transmit.
Setting
ENXMT = 1 enables transmission. With ENXMT = 0, no transmission will occur. If ENXMT is
written as 0 during frame transmission, a packet transmission
which is incomplete will have a
guaranteed
CRC
violation
appended before the internal
Transmit FIFO is cleared. No
subsequent attempts to load the
FIFO should be made until
ENXMT is set and TDTREQ is
asserted. ENXMT is cleared by
activation of the RESET pin or
SWRST bit.
Enable Receive. Setting ENRCV
= 1 enables reception of frames.
With ENRCV = 0, no frames will
be received from the network
into the internal FIFO. When
ENRCV is written as 0, any
receive frame currently in
progress will be completed (and
valid data contained in the
RCVFIFO can be read by the
host) and the MACE device will
enter the monitoring state for
missed packets. Note that
clearing the ENRCV bit disables
the assertion of RDTREQ. If
ENRCV is cleared during re-
ceive activity and remains
cleared for a long time and if the
tail end of the receive frame currently in progress is longer than
the amount of space available in
the Receive FIFO, Receive
FIFO overflow will occur. However, even with RDTREQ deasserted, if there is valid data in the
Receive FIFO to be read, successful slave reads to the
Receive FIFO can be executed
(indicated by valid DTV). It is the
host’s responsibility to avoid the
overflow situation. ENRCV is
cleared by activation of the
RESET pin or SWRST bit.
PLS Configuration
Control (PLSCC)
(REG ADDR 14)
All bits within the PLS Configuration Control register
are cleared upon a hardware or software reset. Bit
assignments are as follows:
RES
Bit
RES
RES
RES
Name
Bit 7-4
RES
Bit 3
XMTSEL
Bit 2-1
PORTSEL
[1-0]
Am79C940
XMTSEL
PORTSEL [1-0]
ENPLSIO
Description
Reserved. Read as zeroes.
Always write as zeroes.
Transmit Mode Select. XMTSEL
provides control over the AUI
DO+ and DO– operation while
the MACE device is not transmitting. With XMTSEL = 0, DO+
and DO will be equal during
transmit idle state, providing
zero differential to operate transformer coupled loads. The turn
off and return to zero delays are
controlled
internally.
With
XMTSEL = 1, DO+ is positive
with respect to DO during the
transmit idle state .
Port Select. PORTSEL is used
to select between the AUI,
10BASE–T, DAI or GPSI ports
of the MACE device. PORTSEL
is cleared by hardware or software reset. PORTSEL will determine which of the interfaces is
used during normal operation, or
tested when utilizing the loopback options (LOOP [1-0]) in the
User Test Register. Note that
the PORTSEL [1–0] programming will be overridden if the
ASEL bit in the PHY Configuration Control register is set.
67
PORTSEL Interface Definition
PORTSEL
[1–0]
Active
Interface
DXCVR Pin
00
AUI
LOW
01
10BASE–T
HIGH
10
DAI Port
HIGH
11
GPSI
LOW
Bit 0
ENPLSIO
Enable PLS I/O. ENPLSIO is
used to enable the optional I/O
functions from the PLS function.
The following pins are affected
by the ENPLSIO bit: RXCRS,
TXDAT+,
RXDAT,
TXEN,
TXDAT-,
CLSN,
STDCLK,
RDCLK and SRD. Note that if an
external SIA is being utilized via
the GPSI, PORTSEL [1–0] = 11
must be programmed before
ENPLSIO is set, to avoid contention of clock, data and/or
carrier indicator signals.
PHY Configuration
Control (PHYCC)
Bit
Bit 7
68
REVPOL DAPC
Name
LNKFL
DLNKTST
Bit 5
REVPOL
Bit 4
DAPC
Bit 3
LRT
Bit 2
ASEL
Bit 1
RWAKE
(REG ADDR 15)
All bits within the PHY Configuration Control register
with the exception of LNKFL, are cleared by hardware
or software reset. Bit assignments are as follows:
LNKFL DLNKTST
Bit 6
LRT
ASEL
RWAKE
AWAKE
Description
Link Fail. Reports the link integrity of the 10BASE–T receiver.
When the link test function is
enabled (DLNKTST = 0), the
absence of link beat pulses on
the RXD± pair will cause the
integrated 10BASE–T transceiver to go into the link fail state. In
the link fail state, data transmission, data reception, data loopback and the collision detection
functions are disabled, and
remain disabled until valid data
or >5 consecutive link pulses
appear on the RXD± pair. During
link fail, the LNKFL bit will be set
and the LNKST pin should be
externally pulled HIGH. When
the link is identified as functional, the LNKFL bit will be cleared
and the LNKST pin is driven
LOW, which is capable of directly driving a Link OK LED. In
order to inter-operate with systems which do not implement
Link Test, this function can be
disabled
by
setting
the
Am79C940
DLNKTST bit. With Link Test
disabled (DLNKTST = 1), the
data driver, receiver and loopback functions as well as collision detection remain enabled
irrespective of the presence or
absence of data or link pulses on
the RXD± pair. The transmitter
will continue to generate link
beat pulses during periods of
transmit data inactivity. Set by
hardware or software reset.
Disable Link Test. When set, the
integrated 10BASE–T transceiver will be forced into the link pass
state, regardless of receive link
test pulses or receive packet
activity.
Reversed Polarity. Indicates the
receive polarity of the RD± pair.
When normal polarity is detected, the REVPOL bit will be
cleared, and the RXPOL pin
(capable of driving a Polarity OK
LED) will be driven LOW. When
reverse polarity is detected, the
REVPOL bit will be set, and the
RXPOL pin should be externally
pulled HIGH.
Disable Auto Polarity Correction.
When set, the automatic polarity
correction will be disabled.
Polarity detection and indication
will still be possible via the
RXPOL pin.
Low Receive Threshold. When
set, the threshold of the twisted
pair receiver will be reduced by
4.5 dB, to allow extended distance operation.
Auto Select. When set, the
PORTSEL [1-0] bits are overridden, and the MACE device will
automatically select the operating media interface port. When
the 10BASE–T transceiver is in
the link pass state (due to receiving valid packet data and/or Link
Test pulses or the DLNKTST bit
is set), the 10BASE-T port will be
used. When the 10BASE–T port
is in the link fail state, the AUI
port will be used. Switching
between the ports will not occur
during transmission in order to
avoid any type of fragment
generation.
Remote Wake. When set prior to
the SLEEP pin being activated,
the AUI and 10BASE–T receiver
sections and the EADI port will
continue to operate even during
SLEEP. Incoming packet activity
will be passed to the EADI port
pins permitting detection of specific frame contents used to initiate a wake-up sequence.
RWAKE must be programmed
prior to SLEEP being asserted
for this function to operate.
RWAKE is not cleared by
SLEEP, only by activation of the
SWRST bit or RESET pin.
Bit 0
AWAKE
Auto Wake. When set prior to
the SLEEP pin being activated,
the 10BASE-T receiver section
will continue to operate even
during SLEEP, and will activate
the LNKST pin if Link Pass is
detected. AWAKE must be programmed prior to SLEEP being
asserted for this function to
operate. AWAKE is not cleared
by SLEEP, only by activation of
the SWRST bit or RESET pin.
Chip Identification Register
(CHIPID [15-00])
(REG ADDR 16 &17)
This 16-bit value corresponds to the specific version of
the MACE device being used. The value will be
programmed to X940h, where X is a value dependent
on version. [For the current version of the MACE device, X = 3 to denote Rev C0 silicon.]
CHIPID [07–00]
CHIPID [15–08]
Internal Address
Configuration (IAC)
(REG ADDR 18)
This register allows access to and from the multi-byte
Physical Address and Logical Address Filter locations,
using only a single byte location.
The MACE device will reset the IAC register PHYADDR
and LOGADDR bits after the appropriate number of
read or write cycles have been executed on the Physical
Address Register or the Logical Address Filter. Once the
LOGADDR bit is set, the MACE device will reset the bit
after 8 read or write operations have been performed.
Once the PHYADDR bit is set, the MACE device will
reset the bit after 6 read or write operations have been
performed. The MACE device makes no distinction between read or write operations, advancing the internal
address RAM pointer with each access. If both PHYADDR and LOGADDR bits are set, the MACE device
will accept only the LOGADDR bit. If the PHYADDR bit
is set and the Logical Address Filter location is accessed, a DTV will not be returned. Similarly, if the
LOGADDR bit is set and the Physical Address Register
location is accessed, DTV will not be returned. PHY-
ADDR or LOGADDR can be set in the same cycle as
ADDRCHG.
ADDRCHG
Bit
RES
RES
Name
RES
RES
PHYADDR
LOGADDR
RES
Description
Bit 7
ADDRCHG Address Change. When set,
allows the physical and/or logical address to be read or programmed. When ADDRCHG is
set, ENRCV will be cleared, the
MPC will be stopped, and the
last or current in progress
receive frame will be received as
normal. After the frame completes, access to the internal
address RAM will be permitted,
indicated by the MACE device
clearing the ADDRCHG bit.
Please refer to the register
description of the ENRCV bit in
the MAC Configuration Control
register (REG ADDR 13) for the
effect of clearing the ENRCV bit.
Normal reception can be
resumed once the physical/logical address has been changed,
by setting ENRCV.
Bit 6-3 RES
Reserved. Read as zeroes.
Always write as zeroes.
Bit 2
PHYADDR Physical Address Reset. When
set, successive reads or writes
to the Physical Address Register
will occur in the order PADR
[07–00], PADR [15–08],....,
PADR [47–40]. Each read or
write operation on the PADR
location will auto-increment the
internal pointer to access the
next most significant byte.
Bit 1
LOGADDR Logical Address Reset. When
set, successive reads or writes
to the Logical Address Filter will
occur in the order LADRF [07–
00], LADRF [15-08],....,LADRF
[63–56]. Each read or write
operation on the LADRF location
will auto-increment the internal
pointer to access the next most
significant byte.
Bit 0
RES
Reserved. Read as zero. Always
write as zero.
Logical Address Filter
(LADRF [63–00])
(REG ADDR 20)
LADRF [63–00]
This 64-bit mask is used to accept incoming Logical
Addresses. The Logical Address Filter is expected to
be programmed at initialization (after hardware or
Am79C940
69
software reset). After a hardware or software reset and
before the ENRCV bit in the MAC Configuration Control register has been set, the Logical Address can be
accessed by setting the LOG ADDR bit in the Internal
Address Configuration register (REG ADDR 18) and
then by performing 8 reads or writes to the Logical
Address Filter. Once ENRCV has been set, the ADDR
CHG bit in the Internal Address Configuration register
must be set and be polled until it is cleared by the
MACE device before setting the LOGADDR bit and
before accessing of the Logical Address Filter is
allowed.
address and is compared against the value stored in
the Physical Address Register at initialization.
The Logical Address Filter is used in multicast addressing schemes. The acceptance of the incoming frame
based on the filter value indicates that the message
may be intended for the node. It is the user’s responsibility to determine if the message is actually intended
for the node by comparing the destination address of
the stored message with a list of acceptable logical
addresses.
The Broadcast address, which is all ones, does not go
through the Logical Address Filter and is always
enabled provided the Disable Receive Broadcast bit
(DRCVBC in the MAC Configuration Control register) is
cleared. If the Logical Address Filter is loaded with all
zeroes (and PROM = 0), all incoming logical addresses
except broadcast will be rejected.
If the least significant address bit of a received
message is set (Destination Address bit 00 = 1), then
the address is deemed logical, and passed through the
FCS generator. After processing the 48-bit destination
address, a 32-bit resultant FCS is produced and
strobed into an internal register. The high order 6-bits
of this resultant FCS are used to select one of the 64-bit
positions in the Logical Address Filter (see diagram). If
the selected filter bit is a 1, the address is accepted and
the packet will be placed in memory.
Multicast addressing can only be performed when
using external loopback (LOOP [1–0] = 0) by programming RCVFCSE = 1 in the User Test Register.
The FCS logic is internally allocated to the receiver
section, allowing the FCS to be computed on the incoming logical address.
The first bit of the incoming address must be a 1 for a
logical address. If the first bit is a 0, it is a physical
Received Message
Destination Address
47
1 0
1
31
32-Bit Resultant CRC
0
26
CRC
GEN
63
SEL
Logical
Address
Filter
(LADRF)
0
64
MUX
MATCH*
6
MATCH = 1: Packet Accepted
MATCH = 0: Packet Rejected
Logical Address Match Logic
70
Am79C940
16235D-10
Physical Address
(PADR [47-00])
(REG ADDR 21)
PADR [47–00]
This 48-bit value represents the unique node value
assigned by the IEEE and used for internal address
comparison. After a hardware or software reset and
before the ENRCV bit in the MAC Configuration Control register has been set, the Physical Address can be
accessed by setting the PHYADDR bit in the Internal
Address Configuration register (REG ADDR 18) and
then by performing 6 reads or writes to the Physical
Address. Once ENRCV has been set, the ADDRCHG
bit in the Internal Address Configuration register must
be set and be polled until it is cleared by the MACE
device before setting the PHYADDR bit and before
accessing of the Physical Address is allowed. The first
bit of the incoming address must be a 0 for a physical
address. The incoming address is compared against
the value stored in the Physical Address register at initialization provided that the DRCVPA bit in the MAC
Configuration Control register is cleared.
Missed Packet Count (MPC)
(REG ADDR 24)
MPC [7–0]
The Missed Packet Count (MPC) is a read only 8-bit
counter. The MPC is incremented when the receiver is
unable to respond to a packet which would have normally been passed to the host. The MPC will be reset
to zero when read. The MACE device will be deaf to
receive traffic due to any of the following conditions:
■ The host disabled the receive function by clearing
the ENRCV bit in the MAC Configuration Control
register.
■ A Receive FIFO overflow condition exists, and must
be cleared by reading the Receive FIFO and the
Receive Frame Status.
■ The Receive Frame Count (RCVFC) in the FIFO
Frame Count register exceeds its maximum value,
indicating that greater than 15 frames are in the
Receive FIFO.
■ The packet must pass the internal address match to
be counted. Any of the following address match
conditions will increment MPC while the receiver is
deaf:
Physical Address match;
Logical Address match;
Broadcast reception;
Any receive in promiscuous mode (PROM = 1 in the
MAC Configuration Control register);
EADI feature match mode and EAM is asserted;
EADI feature reject mode and EAR is not asserted.
■ Any packet which suffers a collision within the slot
time will not be counted.
■ Runt packets will not be counted unless RPA in the
User Test Register is enabled.
■ Packets which pass the address match criteria but
experience FCS or Framing errors will be counted,
since they are normally passed to the host.
Runt Packet Count (RNTPC)
(REG ADDR 26)
RNTPC [7–0]
The Runt Packet Count (RNTPC) is a read only 8-bit
counter, incremented when the receiver detects a runt
packet that is addressed to this node. Runt packets are
defined as received frames which passed the internal
address match criteria but did not contain a minimum
of 64-bytes of data after SFD. Note that the RNTPC
value returned in the Receive Frame Status (RFS2) will
freeze at a value of 255, whereas this register based
version of RNTPC is free running. The value will roll
over after 255 runt packets have been detected, setting
the RNTPCO bit (in the Interrupt Register and asserting the INTR pin if the corresponding mask bit (RNTPCOM in the Interrupt Mask Register) is cleared.
RNTPC will be reset to zero when read.
Receive Collision Count (RCVCC)(REG ADDR 27)
RCVCC [7–0]
If the number of received frames that have been
missed exceeds 255, the MPC will roll over and continue counting from zero, the MPCO (Missed Packet
Count Overflow) bit in the Interrupt Register will be set
(at the value 255), and the INTR pin will be asserted
providing that MPCOM (Missed Packet Count Overflow
Mask) in the Interrupt Mask Register is clear. MPCOM
will be cleared (the interrupt will be unmasked) after a
hardware or software reset.
The Receive Collision Count (RCVCC) is a read only
8-bit counter, incremented when the receiver detects a
collision on the network. Note that the RCVCC value
returned in the Receive Frame Status (RFS3) will
freeze at a value of 255, whereas this register based
version of RCVCC is free running. The value will roll
over after 255 receive collisions have been detected,
setting the RCVCCO bit (in the Interrupt Register and
asserting the INTR pin if the corresponding mask bit
(RCVCCOM in the Interrupt Mask Register) is cleared.
RCVCC will be reset to zero when read.
Note that the following conditions apply to the MPC:
User Test Register (UTR)
■ After hardware or software reset, the MPC will not
increment until the first time the receiver is enabled
(ENRCV = 1). Once the receiver has been enabled,
the MPC will count all missed packet events,
regardless of the programming of ENRCV.
The User Test Register is used to put the chip into test
configurations. All bits within the Test Register are
cleared upon a hardware or software reset. Bit
assignments are as follows:
RTRE
RTRD
RPA
FCOLL
(REG ADDR 29)
RCVFCSE
LOOP [1-0]
FD_TEST
71
Bit
Bit 7
Bit 6
Bit 5
Bit 4
Bit3
72
Name
Description
RTRE
Reserved Test Register Enable.
Access to the Reserved Test
Registers should not be attempted by the user. Note that
access to the Reserved Test
Register may cause damage
to the MACE device if configured in a system board application. Access to the Reserved
Test Register is prevented,
regardless of the state of RTRE,
once RTRD has been set. RTRE
is cleared by activation of the
RESET pin or SWRST bit.
RTRD
Reserved Test Register Disable.
When set, access to the
Reserved Test Registers is
inhibited, and further writes to
the RTRD bit are ignored.
Access to the Reserved Test
Register is prevented, regardless of the state of RTRE, once
RTRD has been set. RTRD can
only be cleared by hardware or
software reset.
RPA
Runt Packet Accept. Allows
receive packets which are less
than the legal minimum as specified by IEEE 802.3/Ethernet, to
be passed to the host interface
via the Receive FIFO. The
receive packets must be at least
8 bytes (after SFD) in length to
be accepted. RPA is cleared by
activation of the RESET pin or
SWRST bit.
FCOLL
Force Collision. Allows the collision logic to be tested. The
MACE device should be in an
internal loopback test for the
FCOLL test. When FCOLL = 1, a
collision will be forced during the
next transmission attempt. This
will result in 16 total transmission attempts (if DRTRY = 0)
with the Retry Error reported in
the Transmit Frame Status register. FCOLL is cleared by the
activation of the RESET pin or
SWRST bit.
RCVFCSE Receive FCS Enable. Allows the
hardware associated with the
FCS generation to be allocated
to the transmitter or receiver during loopback diagnostics. When
clear, the FCS will be generated
and appended to the transmit
message (providing that DXMTFCS in the Transmit Frame Con-
Bit 2-1
trol is clear), and received after
the loopback process through
the Receive FIFO. When set, the
hardware associated with the
FCS generation is allocated to
the receiver. A transmit packet
will be assumed to contain the
FCS in the last four bytes of the
frame passed through the
Transmit FIFO. The received
frame will have the FCS calculated on the data field and compared with the last four bytes
contained in the received message. An FCS error will be
flagged in the Received Status
(RFS1) if the received and calculated values do not match.
RCVFCSE is only valid when in
any one of the loopback modes
as defined by LOOP [0–1]. Note
that if the receive frame is
expected to be recognized on
the basis of a multicast address
match, the FCS logic must be
allocated
to
the
receiver
(RCVFCSE = 1). RCVFCSE is
cleared by activation of the
RESET pin or SWRST bit.
LOOP [1-0] Loopback Control. The loopback
functions allow the MACE
device to receive its own transmitted frames. Three levels of
loopback are provided as shown
in the following table. During
loopback operation a multicast
address can only be recognized
if RCVFCSE = 1. LOOP [0-1] are
cleared by activation of the
RESET pin or SWRST bit
Loopback Functions
Loop [1–0]
Function
00
No Loopback
01
External Loopback
10
Internal Loopback, excludes
MENDEC
11
Internal Loopback, includes
MENDEC
External loopback allow the
MACE device to transmit to the
physical medium, using either
the AUI, 10BASE–T, DAI or
GPSI port, dependent on the
PORTSEL [1–0] bits in the PLS
Configuration Control register.
Using the internal loopback test
will ensure that transmission
Bit 0
FD_TEST
does not disturb the physical
medium and will prohibit frame
reception from the network. One
Internal loopback function includes the MENDEC in the loop.
Full Duplex Test. When set, will
allow the MACE device to
transmit back to back packets
with 9.6 µs IPG regardless of
receive activities. The setting of
this bit should also be in
conjunction with the setting of
Bit 0 of the Transmit Frame Control (XMTFC) (REG ADDR 2).
The setting of Bit 0 of the
XMTFC register will cause disabling of transmit FCS.
To activate Full Duplex Test mode, program the MACE
device into external loopback mode (EXLOOP=1,
INLOOP=0) and set FD_TEST=1. The code sequence
would be as follows:
write 2 08 ;register XMTFC, transmit FCS disable
write 29 0b ;register UTR, receive FCS enable external
loop enable, full duplex enable
Reserved Test Register 1 (RTR1)
(REG ADDR 30)
Reserved for AMD internal use only.
Reserved Test Register 2 (RTR2) (REG ADDR 31)
Reserved for AMD internal use only.
73
Register Table Summary
Address
Mnemonic
0
RCVFIFO
Receive FIFO [15–00]
Read only
1
XMTFIFO
Transmit FIFO [15–00]
Write only
2
XMTFC
Transmit Frame Control
Read/Write
3
XMTFS
Transmit Frame Status
Read only
4
XMTRC
Transmit Retry Count
Read only
5
RCVFC
Receive Frame Control
Read/Write
6
RCVFS
Receive Frame Status (4-bytes)
Read only
7
FIFOFC
FIFO Frame Count
Read only
8
IR
Interrupt Register
Read only
9
IMR
Interrupt Mask Register
Read/Write
10
PR
Poll Register
Read only
11
BIUCC
BIU Configuration Control
Read/Write
12
FIFOCC
FIFO Configuration Control
Read/Write
13
MACCC
MAC Configuration Control
Read/Write
14
PLSCC
PLS Configuration Control
Read/Write
15
PHYCC
PHY Configuration Control
Read/Write
16
CHIPID
Chip Identification Register [07–00]
Read only
17
CHIPID
Chip Identification Register [15–08]
Read only
18
IAC
Internal Address Configuration
Read/Write
19
Reserved
Comments
Read/Write as 0
20
LADRF
Logical Address Filter (8-bytes)
Read/Write
21
PADR
Physical Address (6-bytes)
Read/Write
22
Reserved
Read/Write as 0
23
Reserved
Read/Write as 0
24
MPC
25
Missed Packet Count
Reserved
Read only
Read/Write as 0
26
RNTPC
Runt Packet Count
Read only
27
RCVCC
Receive Collision Count
Read only
28
74
Contents
Reserved
Read/Write as 0
29
UTR
User Test Register
Read/Write
30
RTR1
Reserved Test Register 1
Read/Write as 0
31
RTR2
Reserved Test Register 2
Read/Write as 0
Register Bit Summary
16-Bit Registers
0
RCVFIFO [15–0]
1
XMTFIFO [15–0]
8-Bit Registers
Address
Mnemonic
2
DRTRY
RES
RES
RES
DXMTFCS
RES
RES
3
XMTSV
UFLO
LCOL
MORE
ONE
DEFER
LCAR
4
EXDEF
RES
RES
RES
5
RES
RES
RES
RES
6
APADXMT
XMTRC [3–0]
LLRCV
RES
M/R
ASTRPRCV
RCVFS [31–00]
7
RCVFC [3–0]
XMTFC [3–0]
8
JAB
BABL
CERR
RCVCCO
RNTPCO
MPCO
RCVINT
XMTINT
9
JABM
BABLM
CERRM
RCVCCOM
RNTPCOM
MPCOM
RCVINTM
XMTINTM
10
XMTSV
TDTREQ
RDTREQ
RES
11
RES
BSWP
12
13
XMTFW [1–0]
PROM
DXMT2PD
RES
RES
RES
RES
XMTSP [1–0]
RES
RES
RES
SWRST
RCVFW [1–0]
XMTFWU
RCVFWU
XMTBRST
RCVBRST
RES
DRCVPA
DRCVBC
ENXMT
ENRCV
EMBA
14
RES
RES
RES
RES
XMTSEL
15
LNKFL
DLNKTST
REVPOL
DAPC
LRT
16
CHIPID [07–00]
17
CHIPID [15–08]
18
ADDRCHG
RES
RES
RES
RES
19
RESERVED
20
LADRF [63–00]
21
PADR [47–00]
22
RESERVED
23
RESERVED
24
MPC [7–0]
25
RESERVED
26
RNTPC [7–0]
27
RCVCC [7–0]
28
RESERVED
29
RTRE
RTRD
RPA
FCOLL
PORTSEL [1–0]
RWAKE
AWAKE
PHYADDR
LOGADDR
RES
RCVFCSE
30
RESERVED
31
RESERVED
ENPLSIO
ASEL
LOOP [1–0]
RES
Receive Frame Status
Address
Mnemonic
RFS0
RCVCNT [7:0]
RFS1
OFLO
CLSN
FRAM
RFS2
RNTPC [7–0]
RFS3
RCVCC [7–0]
FCS
RCVCNT [10:8]
75
Programmer’s Register Model
Addr Mnemonic
Contents
R/W
0
RCVFIFO
Receive FIFO–16 bits
RO
1
XMTFIFO
Transmit FIFO–16 bits
WO
2
XMTFC
3
4
5
XMTFS
XMTRC
RCVFC
Transmit Frame Control
80
DRTRY
Disable Retry
08
DXMTFC
Disable Transmit FCS
01
APADXMT
Auto Pad Transmit
R/W
Transmit Frame Status
80
XMTSV
Transmit Status Valid
40
UFLO
Underflow
20
LCOL
Late Collision
10
MORE
MORE than one retry was needed
08
ONE
Exactly ONE retry occurred
04
DEFER
Transmission was deferred
02
LCAR
Loss of Carrier
01
RTRY
Transmit aborted after 16 attempts
Excessive Defer
80
EXDEF
40
–
20
–
10
–
0F
XMTRC [3:0]
R/W
RO
4-bit Transmit Retry Count
Receive Frame Control
08
LLRCV
Low Latency Receive
04
M/R
Match/Reject for external address detection
01
ASTRPRCV
Auto Strip Receive–Strips pad and FCS from
R/W
received frames
6
RCVFS
Receive Frame Status–4 bytes–read in 4 read cycles
RFS0
RCVCNT [7:0] Receive Message Byte Count
RFS1
RCVSTS, RCVCNT [11:8]–Receive Status & Receive Msg Byte Count MSBs
80
OFLO
Receive FIFO Overflow
40
CLSN
Collision during reception
20
FRAM
Framing Error
10
FCS
RO
FCS (CRC) error
0F
RCVCNT [11:8] 4 MSBs of Receive Msg. Byte Count
RFS2
RNTPC [7:0]
Runt Packet Count (since last successful reception)
RFS3
RCVCC [7:0]
Receive Collision Count (since last successful
reception)
7
76
FIFOFC
FIFO Frame Count
RO
F0
RCVFC
Receive Frame Count–# of RCV frames in FIFO
0F
XMTFC
Transmit Frame Count–# of XMT frames in FIFO
RO
Addr Mnemonic
8
9
IR
IMR
Contents
Interrupt Register
80
JAB
Jabber Error–Excessive transmit during (20–150ms)
40
BABL
Babble Error➔ 1518 bytes transmitted
20
CERR
Collision Error–No SQE Test Message
10
RCVCCO
Receive Collision Count Overflow–Red Add 27 overflow
08
RNTPCO
Runt Packet Count Overflow–Reg Addr 26 overflow
04
MPCO
Missed Packet Count Overflow–Reg Addr 24 overflow
02
RCVINT
Receive Interrupt–Host has read last byte of packet
01
XMTINT
Transmit Interrupt–Transmission is complete
PR
JABM
Jabber Error Mask
40
BABLM
Babble Error Mask
20
CERRM
Collision Error Mask
10
RCVCCOM
Receive Collision Count Overflow Mask
08
RNTPCOM
Runt Packet Count Overflow Mask
04
MPCOM
Missed Packet Count Overflow Mask
02
RCVINTM
Receive Interrupt Mask
01
XMTINTM
Transmit Interrupt Mask
Poll Register
80
11
BIUCC
RO
Interrupt Mask Register
80
10
R/W
XMTSV
Transmit Status Valid
40
TDTREQ
Transmit Data Transfer Request
20
RDTREQ
Receive Data Transfer Request
R/W
RO
Bus Interface Unit Configuration Control
80
–
40
BSWP
30
XMTSP–Transmit Start Point (2 bits)
01
Byte Swap
00
Transmit after 4 bytes have been loaded
01
Transmit after 16 bytes have been loaded
10
Transmit after 64 bytes have been loaded
11
Transmit after 112 bytes have been loaded
SWRST
Software Reset
R/W
77
Programmer’s Register Model (continued)
Addr
Mnemonic
12
FIFOCC
Contents
R/W
FIFO Configuration Control
C0
XMTFW
30
Transmit FIFO Watermark (2 bits)
00
Assert TDTREQ after 8 write cycles can be made
01
Assert TDTREQ after 16 write cycles can be made
10
Assert TDTREQ after 32 write cycles can be made
11
XX
RCVFW
Receive FIFO Watermark (2 bits)
00
Assert RDTREQ after 16 bytes are present
01
Assert RDTREQ after 32 bytes are present
10
Assert RDTREQ after 64 bytes are present
11
XX
08
XMTFWU
Transmit FIFO Watermark Update–loads XMTFW bits
04
RCVFWU
Receive FIFO Watermark Update–loads
R/W
RCVFW bits
13
14
MACCC
PLSCC
02
XMBRST
Select Transmit Burst mode
01
RCVBRST
Select Receive Burst mode
Media Access Control (MAC) Configuration Control
80
PROM
Promiscuous mode
40
DXMT2PD
Disable Transmit Two Part Deferral
20
EMBA
Enable Modified Back-off Algorithm
10
–
08
DRCVPA
Disable Receive Physical Address
04
DRCVBC
Disable Receive Broadcast
02
ENXMT
Enable Transmit
01
ENRCV
Enable Receive
Physical Layer Signalling (PLS) Configuration Control
Transmit Mode Select: 1➔ DO± =1 during IDLE
08
XMTSEL
06
PORTSEL [1:0]–Port Select (2 bits)
01
78
R/W
00
AUI selected
01
10BASE-T selected
10
DAI port selected
11
GPSI selected
ENPLSIO
Enable Status
R/W
Programmer’s Register Model (continued)
Addr Mnemonic
15
Contents
PHYCC
R/W
R/W
Physical Layer (PHY) Configuration Control
80
40
20
10
08
04
LNKFL
DLNKTST
REVPOL
DAPC
LRT
ASEL
02
RWAKE
01
AWAKE
Link Fail–Reports 10BASE-T receive inactivity
Disable Link Test–Force 10BASE–T port into Link Pass
Reversed Polarity–Reports 10BASE-T receiver wiring error
Disable Auto Polarity Correction–Detection remains active
Low Receive Threshold–Extended distance capability
Auto Select–Select 10BASE-T port when active, otherwise
AUI
Remote Wake–10BASE-T, AUI and EADI features active during
sleep
Auto Wake–10BASE-T receive and LNKST active during sleep
16
CHIPID
Chip Identification Register LSB–CHIPID [7:0]
RO
17
CHIPID
Chip Identification Register MSB–CHIPID [15:8]
RO
18
IAC
Internal Address Configuration
80
ADDRCHG Address Change–Write to PHYADDR or LOGADDR after ENRCV
40
–
20
–
10
–
08
–
04
–
04
PHYADDR Reset Physical Address pointer
02
LOGADDR Reset Logical Address pointer
01
–
R/W
19
–
Reserved
R/W as 0
20
LADRF
Logical Address Filter–8 bytes–8 reads or writes–LS Byte first
R/W as 0
21
PADR
Physical 6 bytes–6 reads or writes–LS Byte
first
R/W as 0
22
–
Reserved
R/W as 0
23
–
24
MPC
Reserved
R/W as 0
Missed Packet Counter–Number of receive packets missed
R/W as 0
25
–
Reserved
R/W as 0
26
RNTPC
Runt Packet Count–Number of runt packets addressed to this node
R/W as 0
27
RCVCC
Receive Collision Count–Number of receive collision frames on network
R/W as 0
28
–
Reserved
R/W as 0
79
Missing Table Title?
Addr
29
Mnemonic
UTR
Contents
R/W
User Test Register
80
RTRE
Reserved Test Register Enable–must be 0
40
RTRD
Reserved Test Register Disable
20
RPA
Runt Packet Accept
10
FCOLL
Force Collision
08
RCVFCSE
Receive FCS Enable
06
LOOP
Loopback control (2 bits)
00
No loopback
01
External loopback
10
Internal loopback, excludes MENDEC
11
Internal loopback, includes MENDEC
01
–
R/W
R/W
30
–
Reserved
R/W as 0
31
–
Reserved
R/W as 0
SYSTEM APPLICATIONS
Host System Examples
Motherboard DMA Controller
The block diagram shows the MACE device interfacing
to a 8237 type DMA controller. Two external latches are
used to provide a 24 bit address capability. The first
latch stores the address bits A [15:8], which the 8237
will output on the data line DB [7:0], while the signal
ADSTB is active. The second latch is used as a page
register. It extends the addressing capability of the
8237 from 16–bit to 24–bit. This latch must be programmed by the system using an I/0 command to generate the signal LATCHHIGHADR.
The MACE device uses two of the four DMA channels.
One is dedicated to fill the Transmit FIFO and the other
to empty the Receive FIFO. Both DMA channels
should be programmed in the following mode:
— Command Register:
Memory to memory disabled
DREQ sense active high
DACK sense active low
Normal timing
Late Write
Note:
This is the same configuration as used in the IBM PC.
80
The 8237 and the MACE device run synchronous to
the same SCLK. The 8237 is programmed to execute
a transfer in three clock cycles This requires an extra
wait state in the MACE device during FIFO accesses.
A system not using the same configuration as in the
IBM PC can minimize the bus bandwidth required by
the MACE device by programming the DMA controller
in the compressed timing mode.
Care must be taken with respect to the number of
transfers within a burst. The 8237 will drive the signal
EOP low every time the internal counter reaches the
zero. The MACE device however only expects EOF asserted on the last byte/word of a packet. This means,
that the word counter of the 8237 should be initially
loaded with the number of bytes/words in the whole
packet. If the application requires that the packet will be
constructed from several buffers at transmit time, some
extra logic is required to suppress the assertion of EOF
at the end of all but the last buffer transferred by the
DMA controller. Also note that the DMA controller can
only handle either bytes or words at any time. It requires special handling if a packet is transferred to the
MACE device Transmit FIFO in word quantities and it
ends in an odd byte.
The 8237 requires an extra clock cycle to update the
external address latch every 256 transfer cycles. This
example assumes that an update of the external
address latch occurs only at the beginning of the
block transfer.
VDD
CLK
SCLK
DREQ0
RDTREQ
DREQ1
TDTREQ
EOP
DACK0
8237
SCLK
EOF
DACK1
FDS
Am79C940
R/W
ADSTB
CS
DB[7:0]
TC
A[7:0]
DBUS[15:0]
IOW
CSMACE
ADD[4:0]
D[7:0]
Q[7:0]
’373 C
CC
D[7:0]
Q[7:0]
’373
C
CC
LATCHHIGHADR
D[15:0]
A[23:0]
16235D-11
System Interface - Motherboard DMA Example
81
PC/AT Ethernet Adapter Card
SA19-SA0
Remote
Boot
PROM
IEEE
Address
PROM
AUI
I
S
A
DB15
D7-D0
SD7-SD0
Am79C940
B
U
S
RJ45
TP
D15-D8
SD15-SD8
CAM
GPSI/DAI
Header
16235D-12
System Interface - Simple PC/AT Ethernet Adapter Card Example
82
NETWORK INTERFACES
External Address Detection Interface
(EADI)
The address matching, and the support logic necessary to capture and present the relevant data to the external table of address is application specific. Note that
since the entire 802.3 packet after SFD is made available, recognition is not limited to the destination address and/or type fields (Ethernet only).
Inter-networking protocol recognition can be performed
on specific header or LLC information fields.
The External Address Detection Interface can be used
to implement alternative address recognition schemes
outside the MACE device, to complement the physical,
logical and promiscuous detection supported internally.
EADI
Pins
74LS595
SRD
74LS245
SER
SRDCLK
A8-A1
SRCK
SF/BD
EAM/R
CAM
Programming
Interface
Databus
RCK
Q H’
QH-A
B8-B1
74LS595
74LS245
SER
A8-A1
SRCK
Databus
RCK
Q H’
B8-B1
QH-A
Logic
Block
D15-D0
MTCH
Am99C10
16235D-13
EADI Feature - Simple External CAM Interface
83
Attachment Unit Interface (AUI)
The AUI can drive up to 50 m of standard drop cable to
allow the transceiver to be remotely located, as is typically the case in IEEE 803.3 10BASE5 or thick Ethernet® installations. For a locally mounted transceiver,
such as 802.3 10BASE2 or Cheapernet interface, the
isolation transformer requirements between the transceiver and the MACE device can be reduced.
DTE
When used with the Am79C98 TPEX (Twisted Pair
Ethernet Transceiver), the isolation requirements of the
AUI are completely removed providing that the transceiver is mounted locally. For remote location of the
TPEX via an AUI drop cable, the isolation requirement
is necessary to meet IEEE 802.3 specifications for fault
tolerance and recovery.
MAU
AUI
Cable
10BASE5/Ethernet
Am7996
Transceiver
CPU
Memory
Ethernet
Coax
Tap
Am79C940
Power
Supply
Local Bus
16235D-14
AUI-10BASE5/Ethernet Example
10BASE2/Cheapernet
System
CPU
DMA
Engine
Local
Memory
Am79C940
Am7996
Transceiver
I/O Bus
Power
Supply
RG58
BNC “T”
Cheapernet
Coax
16235D-15
AUI-10BASE2/Cheapernet Example
84
10BASE-T/Twisted-Pair Ethernet
RJ45
System
CPU
Other Slave
I/O Device(s)
i.e. SCSI
Am79C9416
Am79C940
MACE
Unshielded
Twisted-Pair
I/O
Processor
Slave Peripheral Bus
16235D-16
10BASE-T/Unshielded Twisted-Pair Interface
85
ANLG +5 V
0.1 µF
0.1 µF
AVDD
Filter &
Transformer
Module
1:1
ANLG GND
AVSS
TXD+
TXP+
TXDTXP-
61.9 Ω
422 Ω
61.9 Ω
422 Ω
Note 2
Note 1
RXD+
LNKST
TD+ 1
TD- 2
XMT
Filter
1.21K Ω
1:1
RD+ 3
RD- 6
RCV
Filter
100Ω
RXD-
RJ45
Connector
DGTL +5 V
LINK OK
RX POL OK
RXPOL
Am79C940
Active Low
DXCVR
Active High Optional
Pulse
Transformer
Note 4
Disable
10BASE2 DC/DC
Convertor
10BASE2 MAU
DO+
DONote 3
DI+
Am7996
DICI+
COAX
TAP
(BNC)
CI40.2 Ω
40.2 Ω
40.2 Ω
0.1 µF
Optional
40.2 Ω
See Am7996 Data Sheet
for component and
implementation details
0.1 µF
ANLG GND
16235D-17
Notes:
1. Compatible filter modules, with a brief description of package type and features are included in the following section.
2. The resistor values are recommended for general purpose use and should allow compliance to the 10BASE-T specification for template
fit and jitter performance. However, the overall performance of the transmitter is also affected by the transmit filter configuration. All
resistors are ± 1%.
3. Compatible AUI transformer modules, with a brief description of package type and features are included in the following section.
4. Active High indicates the external convertor should be turned off. The Disable Transceiver (DXCVR) output is used to indicate the active
network port. A high level indicates the 10BASE-T port is selected and the AUI port is disabled. A low level indicates the AUI port is
selected and the Twisted Pair interface is disabled.
Active Low: indicates the external converter should be turned off. The LNKST output can be used to indicate the active network
port. A high level indicates the 10BASE-T port is in the Link Fail state, and the external convertor should be on. A low level indicates the
10BASE-T port is in the Link Pass state, and the external convertor should be off.
10BASE–T and 10BASE2 Configuration of Am79C940
86
ANLG +5 V
0.1µF
0.1µF
Filter &
Transformer
Module
ANLG GND
AVDD AVSS
TXD+
TXP+
TXDTXP-
61.9Ω
422Ω
1:1
61.9Ω
422Ω
1.21KΩ
Note 2
Note 1
1:1
RD+ 3
RD- 6
RCV
Filter
100Ω
RXD-
TD+ 1
TD- 2
XMT
Filter
RXD+
LNKST
RJ45
Connector
DGTL +5 V
LINK OK
RX POL OK
RXPOL
Am79C940
DGTL GND
Pulse
Transformer
DO+
AUI
Connector
3
DO–
Note 3
DI+
10
5
DI-
12
CI+
2
9
CI40.2Ω
40.2Ω
40.2Ω
0.1µF
Optional
40.2Ω
0.1µF
16235D-18
ANLG GND
Notes:
1. Compatible filter modules, with a brief description of package type and features are included in the following section.
2. The resistor values are recommended for general purpose use and should allow compliance to the 10BASE-T
specification for template fit and jitter performance. However, the overall performance of the transmitter is also
affected by the transmit filter configuration. All resistors are ± 1%.
3. Compatible AUI transformer modules, with a brief description of package type and features are included in the
following section.
10BASE-T and AUI Implementation of Am79C940
87
MACE Compatible 10BASE-T Filters
and Transformers
The table below provides a sample list of MACE compatible 10BASE-T filter and transformer modules
available from various vendors. Contact the respective
manufacturer for a complete and updated listing of
components.
Manufacturer
Part #
Package
Filters
and
Transformers
Filters
Transformers
and Choke
Filters
Transformers
Dual Chokes
Bel Fuse
A556-2006-DE 16–pin 0.3 DIL
✓
Bel Fuse
0556-2006-00
14–pin SIP
✓
Bel Fuse
0556-2006-01
14–pin SIP
✓
Bel Fuse
0556-6392-00
16–pin 0.5 DIL
✓
Halo Electronics
FD02-101G
16–pin 0.3 DIL
Halo Electronics
FD12-101G
16–pin 0.3 DIL
Halo Electronics
FD22-101G
16–pin 0.3 DIL
PCA Electronics
EPA1990A
16–pin 0.3 DIL
PCA Electronics
EPA2013D
16–pin 0.3 DIL
PCA Electronics
EPA2162
16–pin 0.3 SIP
Pulse Engineering
PE-65421
16–pin 0.3 DIL
Pulse Engineering
PE-65434
16–pin 0.3 SIL
✓
Pulse Engineering
PE-65445
16–pin 0.3 DIL
✓
Pulse Engineering
PE-65467
12–pin 0.5 SMT
Valor Electronics
PT3877
16–pin 0.3 DIL
Valor Electronics
FL1043
16–pin 0.3 DIL
Filters
Transformers
Resistors
Dual Chokes
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
MACE Compatible AUI Isolation
Transformers
The table below provides a sample list of MACE compatible AUI isolation transformers available from
vendors. Contact the respective manufacturer for a
complete and updated listing of components
Manufacturer
Part #
.
Package
Description
Bel Fuse
A553-0506-AB
16–pin 0.3 DIL
50 µH
Bel Fuse
S553-0756-AE
16–pin 0.3 SMD
75 µH
Halo Electronics
TD01-0756K
16–pin 0.3 DIL
75 µH
Halo Electronics
TG01-0756W
16–pin 0.3 SMD
75 µH
PCA Electronics
EP9531-4
16–pin 0.3 DIL
50 µH
Pulse Engineering
PE64106
16–pin 0.3 DIL
50 µH
Pulse Engineering
PE65723
16–pin 0.3 SMT
75 µH
Valor Electronics
LT6032
16–pin 0.3 DIL
75 µH
Valor Electronics
ST7032
16–pin 0.3 SMD
75 µH
88
MACE Compatible DC/DC Converters
The table below provides a sample list of MACE compatible DC/DC converters available from various vendors. Contact the respective manufacturer for a
complete and updated listing of components.
Manufacturer
Part #
Package
Voltage
Remote On/Off
Halo Electronics
DCU0-0509D
24–pin DIP
5/-9
No
Halo Electronics
DCU0-0509E
24–pin DIP
5/-9
Yes
PCA Electronics
EPC1007P
24–pin DIP
5/-9
No
PCA Electronics
EPC1054P
24–pin DIP
5/-9
Yes
PCA Electronics
EPC1078
24–pin DIP
5/-9
Yes
Valor Electronics
PM7202
24–pin DIP
5/-9
No
Valor Electronics
PM7222
24–pin DIP
5/-9
Yes
MANUFACTURER CONTACT
INFORMATION
Contact the following companies for further information
on their products.
Company
US. and Domestic
Asia
Europe
33-1-69410402
33-1-69413320
Phone:
(201) 432-0463
852-328-5515
FAX:
(201) 432-9542
852-352-3706
Phone:
(415) 969-7313
65-285-1566
FAX:
(415) 367-7158
65-284-9466
PCA Electronics
Phone:
(818) 892-0761
852-553-0165
(HPC in Hong Kong)
FAX:
(818) 894-5791
852-873-1550
33-1-44894800
33-1-42051579
Phone:
(619) 674-8100
852-425-1651
353-093-24107
FAX:
(619) 675-8262
852-480-5974
353-093-24459
Phone:
(619) 537-2500
852-513-8210
49-89-6923122
FAX:
(619) 537-2525
852-513-8214
49-89-6926542
Bel Fuse
Halo Electronics
Pulse Engineering
Valor Electronics
89
ABSOLUTE MAXIMUM RATINGS
OPERATING RANGES
Storage Temperature . . . . . . . . . . . . -65°C to +150°C
Commercial (C) Devices
Ambient Temperature . . . . . . . . . . . . . . . . . . . . . . . . .
Under Bias . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C
Ambient Temperature (TA) . . . . . . . . . . .0°C to +70°C
Supply Voltage to AVSS
or DVss (AVDD, DVDD) . . . . . . . . . . .-0.3 V to +6.0 V
Ambient Temperature (TA) . . . . . . . . .–40°C to +85°C
Stresses above those listed under Absolute Maximum Ratings may cause permanent device failure. Functionality at or
above these limits is not implied. Exposure to Absolute Maximum Ratings for extended periods may affect device reliability. Programming conditions may differ.
Industrial (I) Devices
VCC Supply Voltages
. . . . . . . . . . . . . . . . . . . . . . (AVDD, DVDD) 5 V ±5%
All inputs within the range: . . AVDD – 0.5 V ≤ Vin ≤
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . AVSS + 0.5 V, or
. . . . . . . . . . . . . . . . . . . . . . . . . DVDD – 0.5 V ≤ Vin ≤
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DVSS + 0.5 V
Operating ranges define those limits between which the functionality of the device is guaranteed.
DC CHARACTERISTICS (Unless otherwise noted, parametric values are the same
between Commercial devices and Industrial devices.)
Parameter
Symbol
VIL
VIH
VILX
VIHX
VSS = 0.0 V
(External Clock Signal)
XTAL1 Input HIGH Voltage
VSS = 0.0 V
VOL
VOH
(External Clock Signal)
Output LOW Voltage
Output HIGH Voltage
IIL1
Input Leakage Current
IIL2
Input Leakage Current
IIH
Input Leakage Current
IIAXD
IIAXC
IILXN
IIHXN
IILXS
IIHXS
IOZ
VAOD
VAODOFF
90
Parameter Description
Input LOW Voltage
Input HIGH Voltage
XTAL1 Input LOW Voltage
Input Current at DI+
and DI–
Input Current at CI+
and CI–
XTAL1 Input LOW Current
Test Conditions
IOL = 3.2 mA
IOH = -0.4 mA (Note 1)
VDD = 5 V, VIN = 0 V
(Note 2)
VDD = 5 V, VIN = 0 V
(Note 2)
VDD = 5 V, VIN = 2.7 V
–0.5
0.8
V
VDD–
VDD+
0.8
0.5
0.45
2.4
V
V
V
–10
10
µA
–200
200
µA
–100
µA
–1 V < VIN < AVDD + 0.5 V
–500
+500
µA
–1 V < VIN < AVDD + 0.5 V
–500
+500
µA
–92
(Note 9)
µA
92
(Note 10)
µA
<10
µA
410
µA
–10
10
µA
RL = 78 Ω
630
1200
mV
RL = 78 Ω (Note 5)
–40
+40
mV
VIN = 0 V
during normal operation
XTAL1 Input LOW Current
SLEEP = HIGH
VIN = 0 V
during Sleep
XTAL1 Input HIGH Current
SLEEP = LOW
VIN = 5.5 V
during Sleep
Output Leakage Current
SLEEP = LOW
0.4 V < VOUT < VDD
(Note 4)
Idle Voltage
Unit
V
V
(Note 3)
SLEEP = HIGH
VIN = 5.5 V
|(DO+)–(DO–)|
Transmit Differential Output
Max
0.8
2.0
during normal operation
XTAL1 Input HIGH Current
Differential Output Voltage
Min
DC CHARACTERISTICS (Continued)
Parameter
Symbol
IAODOFF
VAOCM
VODI
VATH
VASQ
VIRDVD
VICM
VOPD
Parameter Description
Transmit Differential
Output Idle Current
DO± Common Mode
Output Voltage
DO± Differential Output
Voltage Imbalance
Receive Data Differential
Input Threshold
DI± and CI± Differential
Input Threshold Squelch
DI± and CI± Differential
Mode Input Voltage Range
DI± and CI± Input Bias
Voltage
Test Conditions
Min
Max
Unit
RL = 78 Ω
–1
+1
mA
RL = 78 Ω
2.5
AVDD
V
RL = 78 Ω (Note 6)
–25
25
mV
RL = 78 Ω (Note 6)
–35
35
mV
RL = 78 Ω (Note 6)
–160
–275
mV
1.5
V
AVDD –0.8
V
–100
mV
75
mA
100
µA
10
mA
20
mA
500
µA
IIN= 0 mA
AVDD –3.0
DI± Undershoot Voltage at Zero (Note 5)
Differential on Transmit Return
to Zero (ETD)
IDD
Power Supply Current
IDDSLEEP
Power Supply Current
IDDSLEEP
Power Supply Current
IDDSLEEP
Power Supply Current
Twisted Pair Interface
Input Current at RXD±
IIRXD
RXD± Differential Input
RRXD
Resistance
RXD±, RXD– Open Circuit
VTIVB
Input Voltage (Bias)
Differential Mode Input
VTIDV
Voltage Range (RXD±)
RXD Positive Squelch
VTSQ+
Threshold (Peak)
RXD Negative Squelch
VTSQ–
Threshold (Peak)
RXD Post-Squelch
VTHS+
Positive Threshold (Peak)
RXD Post-Squelch
VTHS–
Negative Threshold) (Peak)
RXD Positive Squelch
VLTSQ+
Threshold (Peak)
RXD Negative Squelch
VLTSQ–
Threshold (Peak)
RXD Post-Squelch Positive
VLTHS+
Threshold (Peak)
SCLK = 25 MHz
XTAL1 = 20 MHz
SLEEP Asserted, AWAKE = 0
RWAKE = 1 (Note 7)
SLEEP Asserted, AWAKE = 1
RWAKE = 0 (Note 7)
SLEEP Asserted, AWAKE = 0
RWAKE = 1 (Note 7)
AVSS< VIN < AVDD
(Note 8)
IIN= 0 mA
–500
10
KΩ
AVDD –3.0
AVDD –1.5
V
–3.1
+3.1
V
300
520
mV
–520
–300
mV
150
293
mV
5 MHz ≤ f ≤10 MHz
–293
–150
mV
LRT = LOW
180
312
mV
LRT = LOW
–312
–180
mV
LRT = LOW
90
156
mV
AVDD= +5V
Sinusoid
5 MHz ≤ f ≤10 MHz
Sinusoid
5 MHz ≤ f ≤10 MHz
Sinusoid
5 MHz ≤ f ≤10 MHz
Sinusoid
91
DC CHARACTERISTICS (Continued)
Parameter
Symbol
VLTHS–
VRXDTH
VTXH
VTXL
Parameter Description
RXD Post-Squelch
Negative Threshold (Peak)
RXD Switching Threshold
TXD± and TXD± Output
HIGH Voltage
TXD± and TXD± Output
LOW Voltage
Test Conditions
Min
Max
Unit
LRT = LOW
–156
–90
mV
(Note 4)
–35
35
mV
DVDD –0.6
DVDD
V
DVSS
DVSS + 0.6
V
–40
+40
mV
DVSS = 0V
DVDD = +5V
VTXI
TXD± and TXD± Differential
Output Voltage Imbalance
VTXOFF
TXD± and TXD± Idle Output
Voltage
DVDD = +5V
40
mV
TXD± Differential Driver Output
Impedance
(Note 8)
40
Ω
TXD± Differential Driver Output
Impedance
(Note 8)
80
Ω
RTX
Notes:
1. VOH does not apply to open-drain output pins.
2. IIL1 and IIL2 applies to all input only pins except DI±, CI±, and XTAL1.
IIL1 = ADD4–0, BE1–0, CS, EAM/R, FDS, RESET, RXDAT, R/W, SCLK.
IIL2 = TC, TDI, TCK, TMS.
3. Specified for input only pins with internal pull-ups: TC, TDI, TCK, TMS.
4. IOZ applies to all three-state output pins and bi-directional pins.
5. Test not implemented to data sheet specification.
6. Tested, but to values in excess of limits. Test accuracy not sufficient to allow screening guard bands.
7. During the activation of SLEEP:
–The following pins are placed in a high impedance state: SRD, SF/BD, TXDAT, DXCVR, DTV, TDTREQ, RDTREQ, NTR
and TDO.
–The following I/O pins are placed in a high impedance mode and have their internal TTL level translators disabled:
DBUS15–0, EOF, SRDCLK, RXCRS, RXDAT, CLSN, TXEN, STDCLK and TXDAT+.
–The following input pin has its internal pull-up and TTL level translator disabled: TC.
–The following input pins have their internal TTL level translators disabled and do not have internal pull-ups: CS, FDS,
R/W, ADD4-0, SCLK, BE0, BE1 and EAM/R.
–The following pins are pulled low: XTAL1 (XTAL2 feedback is cut off from XTAL1), TXD+, TXD–, TXP+, TXP–, DO+
and DO.
–The following pins have their input voltage bias disabled: DI+, DI, CI+ and CI.
–AWAKE and RWAKE are reset to zero. IDDSLEEP, with either AWAKE set or RWAKE set, will be much higher and its
value remains to be determined.
8. Parameter not tested.
9. For industrial temperature version, Max value is –150 µA.
10. For industrial temperature version, Max value is +150 µA.
92
AC CHARACTERISTICS (Unless otherwise noted, parametric values are the same
between Commercial devices and Industrial devices.)
No.
Parameter
Symbol
Parameter Description
Test Conditions
Min (ns)
Max (ns)
Clock and Reset Timing
1
tSCLK
SCLK period
40
1000
2
tSCLKL
SCLK LOW pulse width
0.4*tSCLK
0.6*tSCLK
3
tSCLKH
SCLK HIGH pulse width
0.4*tSCLK
0.6*tSCLK
4
tSCLKR
SCLK rise time
5
tSCLKF
SCLK fall time
6
tRST
RESET pulse width
7
tBT
Network Bit Time (BT)=2*tX1 or tSTDC
5
5
15*tSCLK
99
101
49.995
50.005
Internal MENDEC Clock Timing
9
tX1
XTAL1 period
11
tX1H
XTAL1 HIGH pulse width
20
12
tX1L
XTAL1 LOW pulse width
20
13
tX1R
XTAL1 rise time
5
14
tX1F
XTAL1 fall time
5
BIU TIMING (Note 1)
31
tADDS
Address valid setup to SCLK↓
9
32
tADDH
Address valid hold after SCLK↓
2
1. 33
34
tSLVS
tSLVH
CS or FDS and TC, BE1–0,
9
R/W setup to SCLK↓
CS or FDS and TC, BE1–0,
2
R/W hold after SCLK↓
35
tDATD
Data out valid delay from SCLK↓
36
tDATH
Data out valid hold from SCLK↓
37
tDTVD
DTV valid delay from SCLK↓
38
tDTVH
DTV valid hold after SCLK↓
39
tEOFD
EOF valid delay from SCLK↓
40
tEOFH
EOF output valid hold after SCLK↓
41
tCSIS
CS inactive prior to SCLK↓
9
42
tEOFS
EOF input valid setup to SCLK↓
9
43
tEOFH
EOF input valid hold after SCLK↓
44
tRDTD
RDTREQ valid delay from SCLK↓
45
tRDTH
RDTREQ input valid hold after SCLK↓
46
tTDTD
TDTREQ valid delay from SCLK↓
47
tTDTH
TDTREQ input valid hold after SCLK↓
6
48
tDATS
Data in valid setup to SCLK↓
9
49
tDATIH
Data in valid setup after SCLK↓
2
50
tDATE
Data output enable delay from SCLK↓ (Note
3)
0
51
tDATD
Data output disable delay from SCLK↓ (Note
3, 4)
CL = 100 pF (Note 2)
32
6
CL = 100 pF (Note 2)
32
6
CL = 100 pF (Note 2)
32
6
2
CL = 100 pF (Note 2)
32
6
CL = 100 pF (Note 2)
32
25
Notes:
1. The following BIU timing assumes that EDSEL = 1. Therefore, these parameters are specified with respect to the falling edge
of SCLK (SCLK↓). If EDSEL = 0, the same parameters apply but should be referenced to the rising edge of SCLK ↑).
2. Tested with CL set at 100 pF and derated to support the Indicated distributed capacitive Load. See the BIU output valid delay
vs. Load Chart.
3. Guaranteed by design–not tested.
4. tDATD is defined as the time required for outputs to turn high impedence and is not referred to as output voltage lead.
93
AC CHARACTERISTICS (continued)
No.
Parameter
Symbol
Parameter Description
Test Conditions
Min (ns)
Max (ns)
AUI Timing
53
tDOTD
XTAL1 (externally driven) to DO± ουτπυτ
54
tDOTR
DO± rise time (10% to 90%)
2.5
5.0
55
tDOTF
DO± fall time (10% to 90%)
2.5
5.0
56
tDOETM
DO± rise and fall mismatch
57
tDOETD
DO± End of Transmit Delimiter
58
tPWRDI
DI± pulse width to reject
|input| > |VASQ|
59
tPWODI
DI± pulse width to turn on internal DI carrier
sense
|input| > |VASQ|
45
60
tPWMDI
DI± pulse width to maintain internal DI carrier
|input| > |VASQ|
sense on
45
61
tPWKDI
DI± pulse width to turn internal DI carrier
sense off
|input| > |VASQ|
200
62
tPWRCI
CI± pulse width to reject
|input| > |VASQ|
63
tPWOCI
CI± pulse width to turn on internal SQE sense |input| > |VASQ|
26
64
tPWMCI
CI± pulse width to maintain internal SQE
sense on
|input| > |VASQ|
26
65
tPWKCI
CI± pulse width to turn internal SQE sense off |input| > |VASQ|
160
66
tSQED
CI± SQE Test delay from O± inactive
|input| > |VASQ|
67
tSQEL
CI± SQE Test length
|input| > |VASQ|
79
tCLSHI
CLSN high time
80
tTXH
100
1
200
375
15
136
10
90
tSTDC + 30
TXEN or DO± hold time from CLSN↑
|input| > |VASQ|
32*tSTDC
96*tSTDC
DAI Port Timing
94
70
tTXEND
STDCLK↑ delay to TXEN↓
CL = 50 pF
70
72
tTXDD
STDCLK↑ delay to TXDAT± change
CL = 50 pF
70
80
tTXH
TXEN or TXDAT± hold time from CLSN↑
95
tDOTF
Mismatch in STDCLK ≠ to TXEN↓ and
TXDAT± change
96
tTXDTR
TXDAT± rise time
See Note 1
5
97
tTXDTF
TXDAT± fall time
See Note 1
5
98
tTXDTM
TXDAT± rise and fall mismatch
See Note 1
1
99
tTXENETD
TXEN End of Transmit Delimiter
100
tFRXDD
First RXDAT↓ delay to RXCRS↑
100
101
tLRXDD
Last RXDAT ≠ delay to RXCRS↓
120
102
tCRSCLSD
RXCRS↑ delay to CLSN↑ (TXEN = 0)
100
32*tSTDC
96*tSTDC
15
250
350
AC CHARACTERISTICS (continued)
No.
Parameter
Symbol
Parameter Description
Test Conditions
Min (ns)
Max (ns)
99
101
GPSI Clock Timing
17
tSTDC
STDCLK period
18
tSTDCL
STDCLK low pulse width
19
tSTDCH
STDCLK high pulse width
20
tSTDCR
STDCLK rise time
See Note 1
21
tSTDCF
STDCLK fall time
See Note 1
22
tSRDC
SRDCLK period
85
23
tSRDCH
SRDCLK HIGH pulse width
38
24
tSRDCL
SRDCLK LOW pulse width
38
25
tSRDCR
SRDCLK rise time
See Note 1
5
26
tSRDCF
SRDCLK fall time
See Note 1
5
70
tTXEND
STDCLK↑ delay to TXEN↑
(CL = 50 pF)
70
71
tTXENH
TXEN hold time from STDCLK↑
(CL = 50 pF)
72
tTXDD
STDCLK↑ delay to TXDAT+ change (CL = 50 pF)
73
tTXDH
TXDAT+ hold time from STDCLK↑
(CL = 50 pF)
74
tRXDR
RXDAT rise time
See Note 1
8
75
tRXDF
RXDAT fall time
See Note 1
8
76
tRXDH
RXDAT hold time (SRDCLK↑ to
RXDAT change)
25
77
tRXDS
RXDAT setup time (RXDAT stable
to SRDCLK↑)
0
78
tCRSL
RXCRS low time
tSTDC + 20
79
tCLSHI
CLSN high time
tSTDC + 30
80
tTXH
TXEN or TXDAT± hold time from
CLSN↑
32*tSTDC
81
tCRSH
RXCRS hold time from SRDCLK↑
0
See Note 1
45
45
5
5
115
GPSI Timing
5
70
5
96*tSTDC
EADI Feature Timing
85
tDSFBDR
SRDCLK↓ delay to SF/BD↑
20
86
tDSFBDF
SRDCLK↓ delay to SF/BD↑
20
87
tEAMRIS
EAM/R invalid setup prior to
SRDCLK↓ after SFD
88
tEAMS
EAM setup to SRDCLK↓ at bit 6 of
Source Address byte 1 (match
packet)
89
tEAMRL
EAM/R low time
200
90
tSFBDHIH
SF/BD high hold from last
SRDCLK↓
100
91
tEARS
EAR setup SRDCLK↓ at bit 6 of
message byte 64
–150
0
0
(reject normal packet)
Note:
1. Not tested but data available upon request.
95
AC CHARACTERISTICS (continued)
No.
Parameter
Parameter Description
Symbol
Test Conditions
Min
Max
IEEE 1149.1 Timing
109
tTCLK
TCK Period, 50% duty cycle (+5%)
100
110
tsu1
TMS setup to TCK↑
8
111
tsu2
TDI setup to TCK↑
5
112
thd1
TMS hold time from TCK↑
5
113
thd2
TDI hold time from TCK↑
10
114
td1
TCK↓ delay to TDO
30
115
td2
TCK↓ delay to SYSTEM OUTPUT
35
10BASE–T Transmit Timing
Min
Max
250
350
125
tTETD
Transmit Start of Idle
126
tTR
Transmitter Rise Time
(10% to 90%)
5.5
127
tTF
Transmitter Fall Time
(90% to 10%)
5.5
128
tTM
Transmitter Rise and Fall Time Mismatch
129
tXMTON
XMT# Asserted Delay
130
tXMTOFF
XMT# De-asserted Delay
131
tPERLP
Idle Signal Period
132
tPWLP
Idle Link Pulse Width
133
tPWPLP
Predistortion Idle Link Pulse Width
1
100
TBD
TBD
8
24
(Note 1)
75
120
(Note 1)
45
55
134
tJA
Transmit Jabber Activation Time
20
150
135
tJR
Transmit Jabber Reset Time
250
750
136
tJREC
Transmit Jabber Recovery Time (Minimum
Time Gap Between Transmitted Packets to
Prevent Jabber Activation)
1.0
10BASE–T Receive Timing
140
tPWNRD
RXD Pulse Width Not to Turn Off Internal
Carrier Sense
141
tPWROFF
RXD Pulse Width to Turn Off VIN> VTHS
(min)
200
142
tRETD
Receive Start of Idle
200
143
tRCVON
RCV# Asserted Delay
144
tRCVOFF
RCV# De-asserted Delay
Note:
1. Not tested but data available upon request.
96
VIN > VTHS
(min)
136
tRON – 50
TBD
–
tRON – 100
TBD
BIU Output Valid Delay vs. Load Chart
nom+4
nom
BIU Output Valid Delay
from SCLK↓
(ns)
nom-4
nom-8
50
75
100
125
150
CL (pF)
16235D-19
KEY TO SWITCHING WAVEFORMS
WAVEFORM
INPUTS
OUTPUTS
Must be
Steady
Will be
Steady
May
Change
from H to L
Will be
Changing
from H to L
May
Change
from L to H
Will be
Changing
from L to H
Don’t Care,
Any Change
Permitted
Changing,
State
Unknown
Does Not
Apply
Center
Line is HighImpedance
“Off” State
KS000010
97
SWITCHING TEST CIRCUITS
IOL
Sense Point
VTHRESHOLD
CL
IOH
16235D-20
Normal and Three-State Outputs
AVDD
52.3 Ω
DO+
Test Point
DO154 Ω
100 pF
AVSS
16235D-21
AUI DO Switching Test Circuit
DVDD
294 Ω
TXD+
Test Point
TXD100 pF
Includes Test
Jig Capacitance
294 Ω
DVSS
16235D-22
TXD Switching Test Circuit
98
DVDD
715 Ω
TXP+
TXP-
Test Point
715 Ω
100 pF
Includes Test
Jig Capacitance
DVSS
16235D-23
TXP Outputs Test Circuit
AC WAVEFORMS
1
2
3
SCLK
4
5
6
RESET
9
11
12
XTAL1
13
14
Clock and Reset Timing
16235D-24
99
AC WAVEFORMS
SCLK
(EDSEL = 0)
TL
TH
S0
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
SCLK
(EDSEL = 1)
TL
TH
S0
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
31
ADD[4:0]
32
R/W
34
33
41
CS or FDS
35
DBUS[15:0]
51
50
Word N
Word N+1
36
Last Byte
or Word
38
DTV
37
40
EOF
39
BE0-1
34
TC = 1
16235D-25
Host System Interface—2-Cycle Receive FIFO/Register Read Timing
100
AC WAVEFORMS
SCLK
(EDSEL = 0)
TL TH S0 S1 W0 W1 S2 S3 S0
S1 W0 W1 S2
S3 S0 S1 W0 W1 S2 S3 S0
SCLK
(EDSEL = 1)
TL TH S0 S1 W0 W1 S2 S3 S0
S1 W0 W1 S2
S3 S0
S1 W0 W1 S2 S3 S0
31
ADD[4:0]
32
R/W
33
34
41
CS or FDS
51
35
DBUS[15:0]
Word N
Last Byte
or Word
Word N+1
50
38
36
DTV
37
40
EOF
39
BE0-1
TC = 0
34
16235D-26
Host System Interface—3-Cycle Receive FIFO/Register Read Timing
101
AC WAVEFORMS
SCLK
(EDSEL = 0)
TL
TH
S0
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
SCLK
(EDSEL = 1)
TL
TH
S0
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
31
ADD4–0
32
R/W
33
41
34
CS or FDS
48
DBUS15–0
Word N
49
Word N+1
Last Byte
or Word
38
DTV
43
37
EOF
42
BE0-1
34
TC = 1
16235D-27
Host System Interface—2-Cycle Transmit FIFO/Register Write Timing
102
AC WAVEFORMS
SCLK
(EDSEL = 0)
TL TH
S0 S1 W0 W1 S2 S3
S0 S1 W0 W1 S2 S3
S0
S1 W0 W1 S2
S3 S0
SCLK
(EDSEL = 1)
TL TH
S0 S1 W0 W1 S2 S3
S0 S1 W0 W1 S2 S3
S0
S1 W0 W1 S2
S3 S0
31
ADD[4:0]
32
R/W
33
34
41
CS
48
DBUS[15:0]
Word N
Last Byte
or Word
Word N+1
49
38
DTV
37
43
EOF
42
BE0-1
34
TC = 0
16235D-28
Host System Interface—3-Cycle Transmit FIFO/Register Write Timing
SCLK
(EDSEL = 0)
S2
S3
S0
S1
S2
S0
S1
S2
S3
S0
S0
S1
S2
S3
SCLK
(EDSEL = 1)
S2
S3
S0
S1
S2
S0
S1
S2
S3
S0
S0
S1
S2
S3
40
EOF
44
39
Note 1
RDTREQ
45
16235D-29
Note: Once the host detects the EOF output active from the MACE device (S2/S3 edge), if no other receive packet exists
in the RCVFIFO which meets the assert conditions for RDTREQ, the MACE device will deassert RDTREQ within 4 SCLK
cycles (S0/S1 edge). This is consistent for both 2 or 3 cycle read operations.
Host System Interface–RDTREQ Read Timing
103
AC WAVEFORMS
SCLK
(EDSEL = 0)
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
SCLK
(EDSEL = 1)
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
S1
S2
S3
S0
43
EOF
46
42
TDTREQ
Note 1
47
Note 2
Note 3
Notes:
1. TDTREQ will be asserted for two write cycles (4 SCLK cycles) minimum.
16235D-30
2. TDTREQ will deassert 1 SCLK cycle after EOF is detected (S2/S3 edge).
3. When EOF is written, TDTREQ will go inactive for 1 SCLK cycle minimum.
Host System Interface–TDTREQ Write Timing
XTAL1
STDCLK
9
TXEN
1
1
TXDAT+
(Note 1)
1
1
0
0
54
55
DO+
DO–
1
DO±
53
Note: TXDAT+ is the internal version of the signal, and is shown for clarification only.
AUI Transmit Timing–Start of Packet
104
16235D-31
XTAL1
STDCLK
TXEN
1
1
TXDAT+
(Note 1)
0
0
DO+
DO–
DO±
1
0
bit (n–2)
bit (n–1)
57
0
> 200 ns
bit (n)
16235D-32
Note: TXDAT+ is the internal version of the signal, and is shown for clarification only.
AUI Transmit Timing–End of Packet (Last Bit = 0)
XTAL1
SRDCLK
TXEN
TXDAT+
1
1
1
0
(Note 1)
DO+
DO–
DO±
1
bit (n–2)
0
bit (n–1)
57
> 250 ns
bit (n)
Note: TXDAT+ is the internal version of the signal, and is shown for clarification only.
AUI Transmit Timing–End of Packet (Last Bit = 1)
16235D-33
105
57
40 mV
DO±
0V
100 mV Max
80 Bit Times Max
16235D-34
AUI Transmit Timing—End Transmit Delimiter (ETD)
Bit Cell 1
Bit Cell 2
1
DI±
59
Bit Cell 3
0
Bit Cell 4
1
Bit Cell 5
0
1
0
(Note 1)
60
VASQ
BCC
BCB
BCC
BCB
BCC
BCC
BCB
BCC
BCB
RXCRS
IVCO_ENABLE
IVCO
SRDCLK
5 Bit Times Max
SRD
(Note 2)
16235D-35
Notes:
1. Minimum pulse width>45 ns with amplitude >–160 mV.
2. SRD first decoded bit might not be defined until bit time 5.
3. First valid data bit.
4. IVCO and VCO ENABLE are internal signals shown for clarification only.
AUI Receive Timing–Start of Packet
106
(Note 3)
Bit Cell (n–1)
Bit Cell (n)
1
0
61
60
DI±
VASQ
(Note 2)
BCC
BCB
BCC
BCB
RXCRS
(Note 1)
IVCO
SRDCLK
SRD
bit (n)
bit (n–1)
16235D-36
Notes:
1. RXCRS deasserts in less than 3 bit times after last DI± rising edge.
2. Start of next packet reception (2 bit times).
3. IVCO is an internal signal shown for clarification only.
AUI Receive Timing–End of Packet (Last Bit = 0)
Bit Cell (n)
1
Bit Cell (n–1)
0
DI±
61
BCC
BCB
BCC
RXCRS
(Note 1)
IVCO
SRDCLK
SRD
bit (n)
bit (n–1)
16235D-37
Notes:
1. RXCRS deassets in less than 3 bit times after last DI± rising edge.
2. IVCO is an internal signal shown for clarification only.
AUI Receive Timing–End of Packet (Last Bit = 1)
107
DO±
TXEN
CI+
CI-
80
CLSN
79
16235D-38
AUI Collision Timing
DO±
66
CI+
CI-
67
CLSN = 0
AUI SQE Test Timing
108
16235D-39
STDCLK
72
BCB
BCB
BCB
BCB
BCB
BCB
BCB
BCB
TXDAT±
96
99
97
TXDAT+
95
TXDAT-
72
TXEN
16235D-40
DAI Port Transmit Timing
RXDAT
100
101
RXCRS
DAI Port Receive Timing
16235D-41
109
TXDAT+
TXDAT-
TXEN
RXDAT
RXCRS
102
CLSN
79
16235D-42
DAI Port Collision Timing
Destination Address
Byte 2
Destination Address
Byte 1
SRDCLK
SRD
SFD
BIT
0
BIT
1
BIT
2
BIT
3
BIT
4
BIT
5
BIT
6
BIT
7
BIT
0
86
SF/BD
85
Note 1
EAM/R
87
89
Note:FirstassertionofEAM/Rmustoccurafterbit2/3boundaryofpreamble.
EADI Feature Timing–Start of Address
110
16235D-43
Last Byte of Message
SRDCLK
SRD
90
86
SF/BD
85
EADI Feature–End of Packet Timing
Destination Address
Byte 6
16235D-44
Source Address
Byte 1
Source Address
Byte 2
SRDCLK
SRD
BIT
5
BIT
6
BIT
7
BIT
0
BIT
1
BIT
2
BIT
3
BIT
4
BIT
5
BIT
6
BIT
7
BIT
0
86
SF/BD
85
88
EAM
89
16235D-45
EADI Feature-Match Timing
111
Byte 64
(Data Byte 51)
Byte 65
(Data Byte 52)
Byte 66
(Data Byte 53)
RDCLK
BIT
4
SRD
BIT
5
BIT
6
BIT
0
BIT
7
BIT
1
85
BIT
2
BIT
3
BIT
4
BIT
5
BIT
6
BIT
7
BIT
0
BIT
1
86
SF/BD
91
EAR
89
16235D-46
EADI Feature Reject Timing
17
19
18
STDCLK
72
73
20
21
TXDAT+
70
TXEN
Note 1
71
RXCRS
16235D-47
Note: During transmit, the RXCRS input must be asserted (high) and remain active-high after TXEN goes active (high). If
RXCRS is deasserted before TXEN is deasserted, LCAR will be reported (Transmit Frame Status) after the transmission is
completed by the MACE device.
GPSI Transmit Timing
112
22
24
23
SRDCLK
75
77
25
26
RXDAT
76
74
RXCRS
81
78
16235D-48
GPSI Receive Timing
STDCLK
72
73
TXDAT+
70
TXEN
80
CLSN
79
16235D-49
GPSI Collision Timing
113
TCK
tsu1
td1
thd1
TMS
tsu2
TDI
thd2
TDO
td2
System Output
16235D-50
IEEE 1149.1 TAP Timing
tTF
tTF
tTETD
tXMTOFF
Note:
1. Parameter is internal to the device.
10BASE-T Transmit Timing
114
16235D-51
VTSQ+
VTSQtRCVOFF
RXD±
tRCVON
RXCRS
16235D-52
10BASE-T Receive Timing
TXD±
RXD±
tCOLON
tCOLOFF
CLSN
16235D-53
10BASE-T Collision Timing
115
tPWPLP
TXD+
TXP+
TXD-
TXPtPWLP
tPERLP
16235D-54
10BASE-T Idle Link Test Pulse
VTSQ+
VTHS+
RXD±
VTHSVTSQ-
16235D-55
10BASE-T Receive Thresholds (LRT = 0)
VLTSQ+
VLTHS+
RXD±
VLTHSVLTSQ-
10BASE-T Receive Thresholds (LRT = 1)
116
16235D-56
PHYSICAL DIMENSIONS*
PL 084
84-Pin Plastic Leaded Chip Carrier (measured in inches)
1.185
1.195
1.150
1.156
.042
.056
.062
.083
1.090
1.130
1.000
REF
Pin 1 I.D.
1.185
1.195
1.150
1.156
.013
.021
.026
.032
.050 REF
TOP VIEW
.007
.013
.090
.130
.165
.180
SEATING PLANE
SIDE VIEW
117
PHYSICAL DIMENSIONS*
PQR100
100-Pin Plastic Quad Flat Pack; Trimmed and Formed (measured in millimeters)
12.35
REF
13.90
14.10
17.10
17.30
50
30
0.22
0.38
18.85
REF
19.90
20.10
23.00
23.40
0.65
BASIC
Pin 1 I.D.
80
100
TOP VIEW
2.70
2.90
3.35
MAX
0.70
0.90
0.25
MIN
118
SIDE VIEW
17198A
CG 47
7/14/92 SG
PHYSICAL DIMENSIONS
PQR100
100-Pin Plastic Quad Flat Pack with Molded Carrier Ring (measured in millimeters)
35.87
36.13
31.37
35.50
35.90
27.87
28.13
31.63
25.15
25.20
BSC
25.25
13.80
22.15
22.25
14.10
50
30
35.50 27.87 22.15
35.90 28.13 22.25
35.87 31.37 25.15 19.80
36.13 31.63 25.25 20.10
Pin 1 I.D.
80
100
0.22
0.38
TOP VIEW
.65 NOM
.45 Typ
.65 Pitch
2.00 4.80
1.80
.65 Typ
SIDE VIEW
17198A
CB 48
6/25/92 SG
119
PHYSICAL DIMENSIONS*
PQT080
80-Pin Thin Quad Flat Package (measured in millimeters)
80
1
13.80
11.80 14.20
12.20
11.80
12.20
13.80
14.20
11ϒ – 13ϒ
.95
1.05
1.20 MAX
0.50 BSC
1.00 REF.
120
11ϒ – 13ϒ
APPENDIX A
Logical Address Filtering
For Ethernet
The purpose of logical (or group or multicast)
ad dresses is to allow a group of nodes in a network to
receive the same message. Each node can maintain a
list of multicast addresses that it will respond to. The
logical address filter mechanism in AMD Ethernet controllers is a hardware aide that reduces the average
amount of host computer time required to determine
whether or not an incoming packet with a multicast
des tination address should be accepted.
The logical address filter hardware is an implementation of a hash code searching technique commonly
used by software programmers. If the multicast bit in
the destination address of an incoming packet is set,
the hardware maps this address into one of 64 categories then accepts or rejects the packet depending on
whether or not the bit in the logical address filter register corresponding the selected category is set. For
ex ample, if the address maps into category 24, and bit
24 of the logical address filter register is set, the packet
is accepted.
Since there are more than 10 14 possible multicast
ad dresses and only 64 categories, this scheme is far
from unambiguous. This means that the software will
still have to compare the address of a received packet
with its list of acceptable multicast addresses to make
the final decision whether to accept or discard the
packet. However, the hardware prevents the software
from having to deal with the vast majority of the
unac ceptable packets.
The efficiency of this scheme depends on the number
of multicast groups that are used on a particular network and the number of groups to which a node
be longs. At one extreme if a node happens to belong
to 64 groups that map into 64 different categories, the
hardware will accept all multicast addresses, and all filtering must be done by software. At the other extreme
(which is closer to a practical network), if multicast
ad dresses are assigned by the local administrator, and
fewer than 65 groups are set up, the addresses can be
assigned so that each address maps into a different
category, and no software filtering will be needed at all.
In the latter case described above, a node can be made
a member of several groups by setting the appropriate
bits in the logical address filter register. The administrator can use the table Mapping of Logical Address to
Fil ter Mask to find a multicast address that maps into a
particular address filter bit. For example address 0000
0000 00BB maps into bit 15. Therefore, any node that
has bit 15 set in its logical address filter register will
re ceive all packets addressed to 0000 0000 00BB.
(Addresses in this table are not shown in the standard
Ethernet format. In the table the rightmost byte is the
first byte to appear on the network with the least
signif icant bit appearing first).
Driver software that manages a list of multicast
ad dresses can work as follows. First the multicast
ad dress list and the logical address filter must be
ini tialized. Some sort of management function such as
the driver initialization routine passes to the driver a list
of addresses. For each address in the list the driver
uses a subroutine similar to the one listed in the
Am7990 LANCE data sheet to set the appropriate bit in
a software copy of the logical address filter register.
When the complete list of addresses has been
pro cessed, the register is loaded.
Later, when a packet is received, the driver first looks
at the Individual/Group bit of the destination address of
the packet to find out whether or not this is a multicast
address. If it is, the driver must search the multicast
ad dress list to see if this address is in the list. If it is not
in the list, the packet is discarded.
The broadcast address, which consists of all ones is a
special multicast address. Packets addressed to the
broadcast address must be received by all nodes.
Since broadcast packets are usually more common
than other multicast packets, the broadcast address
should be the first address in the multicast address list.
Am79C940
121
MAPPING OF LOGICAL ADDRESS TO FILTER MASK
Byte #
Bit #
LADRF
Bit
0
0
0
0
1
0
122
Destination
Address Accepted
Byte #
Bit #
LADRF
Bit
85 00 00 00 00 00
4
0
32
21 00 00 00 00 00
1
A5 00 00 00 00 00
4
1
33
01 00 00 00 00 00
2
2
E5 00 00 00 00 00
4
2
34
41 00 00 00 00 00
0
3
3
C5 00 00 00 00 00
4
3
35
71 00 00 00 00 00
0
4
4
45 00 00 00 00 00
4
4
36
E1 00 00 00 00 00
0
5
5
65 00 00 00 00 00
4
5
37
C1 00 00 00 00 00
0
6
6
25 00 00 00 00 00
4
6
38
81 00 00 00 00 00
0
7
7
05 00 00 00 00 00
4
7
39
A1 00 00 00 00 00
1
0
8
2B 00 00 00 00 00
5
0
40
8F 00 00 00 00 00
1
1
9
0B 00 00 00 00 00
5
1
41
BF 00 00 00 00 00
1
2
10
4B 00 00 00 00 00
5
2
42
EF 00 00 00 00 00
1
3
11
6B 00 00 00 00 00
5
3
43
CF 00 00 00 00 00
1
4
12
EB 00 00 00 00 00
5
4
44
4F 00 00 00 00 00
1
5
13
CB 00 00 00 00 00
5
5
45
6F 00 00 00 00 00
1
6
14
8B 00 00 00 00 00
5
6
46
2F 00 00 00 00 00
1
7
15
BB 00 00 00 00 00
5
7
47
0F 00 00 00 00 00
2
0
16
C7 00 00 00 00 00
6
0
48
63 00 00 00 00 00
2
1
17
E7 00 00 00 00 00
6
1
49
43 00 00 00 00 00
2
2
18
A7 00 00 00 00 00
6
2
50
03 00 00 00 00 00
2
3
19
87 00 00 00 00 00
6
3
51
23 00 00 00 00 00
2
4
20
07 00 00 00 00 00
6
4
52
A3 00 00 00 00 00
2
5
21
27 00 00 00 00 00
6
5
53
83 00 00 00 00 00
2
6
22
67 00 00 00 00 00
6
6
54
C3 00 00 00 00 00
2
7
23
47 00 00 00 00 00
6
7
55
E3 00 00 00 00 00
3
0
24
69 00 00 00 00 00
7
0
56
CD 00 00 00 00 00
3
1
25
49 00 00 00 00 00
7
1
57
ED 00 00 00 00 00
3
2
26
09 00 00 00 00 00
7
2
58
AD 00 00 00 00 00
3
3
27
29 00 00 00 00 00
7
3
59
8D 00 00 00 00 00
3
4
28
A9 00 00 00 00 00
7
4
60
0D 00 00 00 00 00
3
5
29
89 00 00 00 00 00
7
5
61
2D 00 00 00 00 00
3
6
30
C9 00 00 00 00 00
7
6
62
6D 00 00 00 00 00
3
7
31
E9 00 00 00 00 00
7
7
63
4D 00 00 00 00 00
Am79C940
Destination
Address Accepted
APPENDIX B
BSDL DESCRIPTION OF
Am79C940 MACE JTAG
STRUCTURE
-- -------- 04 November 1996 ------------ JWB 13-AUG-1996 changed "TQFP_PACKAGE" to "TQFP"
-- 31-OCT-1996 corrected reversed bit subscripts for ADD, DBUS !
--
and bumped chip rev version from 2 to 3
-- A separate file for TQFP only, had to be created due to the missing
--
four pins/functions on the TQFP version.
-- The compiler does not know how to handle the missing four pins/functions
--
in the TQFP version while at the same time, available for the PQFP
--
and PLCC versions. We have no further plans for going back to
--
combining both files into a single BSDL file.
--
Network Products Division Product Marketing Group
-- -------------------------------------- BSDL File created/edited by AT&T BSD Editor
--- BSDE:Revision: Silicon Rev. C0; File REV A3
-- BSDE:Description: BSDL File for the AM79C940 MACE Rev C0 Product
-- BSDE:Comments: /* BSDL file for the TQFP Definition only.
--
* BSDL file checked by AT&T’s BCAD2 BSD Editor on 04/03/96
--
*/
entity AM79C940 is
generic (PHYSICAL_PIN_MAP : string := "TQFP" );
port (
ADD: in bit_vector (4 downto 0);
AVDD1: linkage bit;
AVDD2: linkage bit;
AVDD3: linkage bit;
AVDD4: linkage bit;
Am79C940
123
AVSS1: linkage bit;
AVSS2: linkage bit;
BE0_L: in bit;
BE1_L: in bit;
CI0: linkage bit;
CI1: in bit;
CLSN: inout bit;
CS_L: in bit;
DBUS: inout bit_vector (15 downto 0);
DI0: linkage bit;
DI1: in bit;
DO0: linkage bit;
DO1: out bit;
DVDD1: linkage bit;
DVDD2: linkage bit;
DVDDN: linkage bit;
DVDDP: linkage bit;
DVSS1: linkage bit;
DVSS2: linkage bit;
DVSSN1: linkage bit;
DVSSN2: linkage bit;
DVSSN3: linkage bit;
DVSSP: linkage bit;
DXRCV_L: out bit;
EAM_R_L: in bit;
EDSEL: in bit;
EOF_L: inout bit;
FDS_L: in bit;
INTR_L: out bit;
LNKST_L: out bit;
RDTREQ_L: out bit;
RESET_L: in bit;
RXCRS: inout bit;
RXD0: linkage bit;
RXD1: in bit;
RXDAT: inout bit;
R_W_L: in bit;
SCLK: in bit;
SF_BD: out bit;
124
Am79C940
SLEEP_L: in bit;
SRDCLK: inout bit;
STDCLK: inout bit;
TCK: in bit;
TC_L: in bit;
TDI: in bit;
TDO: out bit;
TDTREQ_L: out bit;
TMS: in bit;
TXD0: linkage bit;
TXD1: out bit;
TXDAT1: inout bit;
TXEN_L: inout bit;
TXP0: linkage bit;
TXP1: out bit;
XTAL1: in bit;
XTAL2: linkage bit
);
use STD_1149_1_1990.all;
attribute PIN_MAP of AM79C940 : entity is PHYSICAL_PIN_MAP;
constant TQFP: PIN_MAP_STRING:=
"ADD:(40,39,38,37,36)," &
"AVDD1:52," &
"AVDD2:57," &
"AVDD3:64," &
"AVDD4:69," &
"AVSS1:59," &
"AVSS2:61," &
"BE0_L:31," &
"BE1_L:32," &
"CI0:67," &
"CI1:68," &
"CLSN:78," &
"CS_L:42," &
"DBUS:(27,26,24,23,22,21,20,19,18,17," &
"16,14,13,12,11,9)," &
Am79C940
125
"DI0:65," &
"DI1:66," &
"DO0:62," &
"DO1:63," &
"DVDD1:49," &
"DVDD2:70," &
"DVDDN:25," &
"DVDDP:6," &
"DVSS1:47," &
"DVSS2:73," &
"DVSSN1:10," &
"DVSSN2:15," &
"DVSSN3:28," &
"DVSSP:75," &
"DXRCV_L:71," &
"EAM_R_L:2," &
"EDSEL:72," &
"EOF_L:29," &
"FDS_L:30," &
"INTR_L:7," &
"LNKST_L:43," &
"RDTREQ_L:35," &
"RESET_L:4," &
"RXCRS:80," &
"RXD0:50," &
"RXD1:51," &
"RXDAT:79," &
"R_W_L:41," &
"SCLK:33," &
"SF_BD:3," &
"SLEEP_L:5," &
"SRDCLK:1," &
"STDCLK:76," &
"TCK:46," &
"TC_L:8," &
"TDI:48," &
"TDO:44," &
"TDTREQ_L:34," &
"TMS:45," &
126
Am79C940
"TXD0:54," &
"TXD1:56," &
"TXDAT1:74," &
"TXEN_L:77," &
"TXP0:53," &
"TXP1:55," &
"XTAL1:58," &
"XTAL2:60";
attribute TAP_SCAN_IN
of TDI : signal is true;
attribute TAP_SCAN_OUT
of TDO : signal is true;
attribute TAP_SCAN_MODE
of TMS : signal is true;
attribute TAP_SCAN_CLOCK of TCK : signal is (1.00e+07, BOTH);
attribute INSTRUCTION_LENGTH of AM79C940 : entity is 4;
attribute INSTRUCTION_OPCODE of AM79C940 : entity is
"BYPASS ( 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110," &
" 1111)," &
"EXTEST ( 0000)," &
"IDCODE ( 0001)," &
"SAMPLE ( 0010)," &
"SELFTST ( 0101)," &
"SETBYP ( 0100)," &
"TRIBYP ( 0011)" ;
attribute INSTRUCTION_CAPTURE of AM79C940 : entity is "0001";
attribute INSTRUCTION_DISABLE of AM79C940 : entity is "TRIBYP";
attribute INSTRUCTION_PRIVATE of AM79C940 : entity is
" SELFTST";
attribute IDCODE_REGISTER of AM79C940 : entity is
"0011" &---- version
31-OCT-1996 bumped version from 2 to 3 !
"1001010000000000" &--- part number
"00000000001" &---- manufacturer’s id
"1";----- required by standard
attribute REGISTER_ACCESS of AM79C940 : entity is
Am79C940
127
"BYPASS ( BYPASS, SETBYP, TRIBYP)," &
"BOUNDARY ( EXTEST, SAMPLE, SELFTST)," &
"IDCODE ( IDCODE)";
attribute BOUNDARY_CELLS of AM79C940 : entity is
" BC_1, BC_4";
attribute BOUNDARY_LENGTH of AM79C940 : entity is 99;
attribute BOUNDARY_REGISTER of AM79C940 : entity is
"
0 (BC_1, *, control, 0)," &
"
1 (BC_1, LNKST_L, output3, X, 0, 0, Weak1)," &
"
2 (BC_1, *, internal, 0)," &
"
3 (BC_1, CS_L, input, 1)," &
"
4 (BC_1, R_W_L, input, 1)," &
"
5 (BC_1, ADD(4), input, 0)," &
"
6 (BC_1, ADD(3), input, 0)," &
"
7 (BC_1, ADD(2), input, 0)," &
"
8 (BC_1, ADD(1), input, 0)," &
"
9 (BC_1, ADD(0), input, 0)," &
"
10 (BC_1, *, control, 0)," &
"
11 (BC_1, RDTREQ_L, output3, X, 10, 0, Z)," &
"
12 (BC_1, TDTREQ_L, output3, X, 10, 0, Z)," &
"
13 (BC_4, SCLK, clock, 1)," &
"
14 (BC_1, BE1_L, input, 1)," &
"
15 (BC_1, BE0_L, input, 1)," &
"
16 (BC_1, FDS_L, input, 1)," &
"
17 (BC_1, *, internal, 0)," &
"
18 (BC_1, *, internal, 0)," &
"
19 (BC_1, *, control, 0)," &
"
20 (BC_1, EOF_L, output3, X, 19, 0, Z)," &
"
21 (BC_1, EOF_L, input, 1)," &
"
22 (BC_1, *, control, 0)," &
"
23 (BC_1, DBUS(15), output3, X, 22, 0, Z)," &
"
24 (BC_1, DBUS(15), input, 0)," &
"
25 (BC_1, DBUS(14), output3, X, 22, 0, Z)," &
"
26 (BC_1, DBUS(14), input, 0)," &
"
27 (BC_1, DBUS(13), output3, X, 22, 0, Z)," &
"
28 (BC_1, DBUS(13), input, 0)," &
128
Am79C940
"
29 (BC_1, DBUS(12), output3, X, 22, 0, Z)," &
"
30 (BC_1, DBUS(12), input, 0)," &
"
31 (BC_1, DBUS(11), output3, X, 22, 0, Z)," &
"
32 (BC_1, DBUS(11), input, 0)," &
"
33 (BC_1, DBUS(10), output3, X, 22, 0, Z)," &
"
34 (BC_1, DBUS(10), input, 0)," &
"
35 (BC_1, *, control, 0)," &
"
36 (BC_1, DBUS(9), output3, X, 35, 0, Z)," &
"
37 (BC_1, DBUS(9), input, 0)," &
"
38 (BC_1, DBUS(8), output3, X, 35, 0, Z)," &
"
39 (BC_1, DBUS(8), input, 0)," &
"
40 (BC_1, DBUS(7), output3, X, 35, 0, Z)," &
"
41 (BC_1, DBUS(7), input, 0)," &
"
42 (BC_1, DBUS(6), output3, X, 35, 0, Z)," &
"
43 (BC_1, DBUS(6), input, 0)," &
"
44 (BC_1, DBUS(5), output3, X, 35, 0, Z)," &
"
45 (BC_1, DBUS(5), input, 0)," &
"
46 (BC_1, DBUS(4), output3, X, 35, 0, Z)," &
"
47 (BC_1, DBUS(4), input, 0)," &
"
48 (BC_1, DBUS(3), output3, X, 35, 0, Z)," &
"
49 (BC_1, DBUS(3), input, 0)," &
"
50 (BC_1, DBUS(2), output3, X, 35, 0, Z)," &
"
51 (BC_1, DBUS(2), input, 0)," &
"
52 (BC_1, DBUS(1), output3, X, 35, 0, Z)," &
"
53 (BC_1, DBUS(1), input, 0)," &
"
54 (BC_1, DBUS(0), output3, X, 35, 0, Z)," &
"
55 (BC_1, DBUS(0), input, 0)," &
"
56 (BC_1, TC_L, input, 1)," &
"
57 (BC_1, *, control, 0)," &
"
58 (BC_1, INTR_L, output3, 1, 57, 0, Weak1)," &
"
59 (BC_1, SLEEP_L, input, 1)," &
"
60 (BC_1, RESET_L, input, 1)," &
"
61 (BC_1, *, control, 0)," &
"
62 (BC_1, SF_BD, output3, X, 61, 0, Z)," &
"
63 (BC_1, *, internal, 0)," &
"
64 (BC_1, EAM_R_L, input, 0)," &
"
65 (BC_1, *, control, 0)," &
"
66 (BC_1, SRDCLK, output3, X, 65, 0, Z)," &
"
67 (BC_1, SRDCLK, input, 0)," &
Am79C940
129
"
68 (BC_1, *, control, 0)," &
"
69 (BC_1, RXCRS, output3, X, 68, 0, Z)," &
"
70 (BC_1, RXCRS, input, 0)," &
"
71 (BC_1, *, control, 0)," &
"
72 (BC_1, RXDAT, output3, X, 71, 0, Z)," &
"
73 (BC_1, RXDAT, input, 0)," &
"
74 (BC_1, *, control, 0)," &
"
75 (BC_1, CLSN, output3, X, 74, 0, Z)," &
"
76 (BC_1, CLSN, input, 0)," &
"
77 (BC_1, *, control, 0)," &
"
78 (BC_1, TXEN_L, output3, X, 77, 0, Z)," &
"
79 (BC_1, TXEN_L, input, 0)," &
"
80 (BC_1, *, control, 0)," &
"
81 (BC_1, STDCLK, output3, X, 80, 0, Z)," &
"
82 (BC_1, STDCLK, input, 0)," &
"
83 (BC_1, *, control, 0)," &
"
84 (BC_1, *, internal, 0)," &
"
85 (BC_1, TXDAT1, output3, X, 83, 0, Z)," &
"
86 (BC_1, TXDAT1, input, 1)," &
"
87 (BC_1, EDSEL, input, 1)," &
"
88 (BC_1, *, control, 0)," &
"
89 (BC_1, DXRCV_L, output3, X, 88, 0, Z)," &
"
90 (BC_4, XTAL1, clock, 0)," &
"
91 (BC_1, RXD1, input, 1)," &
"
92 (BC_1, *, control, 0)," &
"
93 (BC_1, TXP1, output3, X, 92, 0, Z)," &
"
94 (BC_1, TXD1, output3, X, 92, 0, Z)," &
"
95 (BC_1, *, control, 0)," &
"
96 (BC_1, DO1, output3, X, 95, 0, Z)," &
"
97 (BC_4, DI1, input, 1)," &
"
98 (BC_4, CI1, input, 1)";
end AM79C940;
=============================================================================
130
Am79C940
---
BSDL File created/edited by AT&T BSD Editor
---
BSDE:Revision: Silicon Rev. C0; File REV A3
--
BSDE:Description: BSDL File for the AM79C940 MACE Product;
--
84-Pin PLCC and 100-Pin PQFP packages.
--
Separate file for 80-Pin TQFP package.
--
BSDE:Comments: /* TQFP Definition has been deleted.
--
* BSDL file checked by AT&T’s BCAD2 BSD Editor on 9/7/95
--
*/
entity AM79C940 is
generic (PHYSICAL_PIN_MAP : string := "PLCC_PACKAGE" );
port (
ADD: in bit_vector (0 to 4);
AVDD1: linkage bit;
AVDD2: linkage bit;
AVDD3: linkage bit;
AVDD4: linkage bit;
AVSS1: linkage bit;
AVSS2: linkage bit;
BE0_L: in bit;
BE1_L: in bit;
CI0: linkage bit;
CI1: in bit;
CLSN: inout bit;
CS_L: in bit;
DBUS: inout bit_vector (0 to 15);
DI0: linkage bit;
DI1: in bit;
DO0: linkage bit;
DO1: out bit;
DTV_L: out bit;
DVDD1: linkage bit;
DVDD2: linkage bit;
DVDDN: linkage bit;
DVDDP: linkage bit;
Am79C940
131
DVSS1: linkage bit;
DVSS2: linkage bit;
DVSSN1: linkage bit;
DVSSN2: linkage bit;
DVSSN3: linkage bit;
DVSSP: linkage bit;
DXRCV_L: out bit;
EAM_R_L: in bit;
EDSEL: in bit;
EOF_L: inout bit;
FDS_L: in bit;
INTR_L: out bit;
LNKST_L: out bit;
RDTREQ_L: out bit;
RESET_L: in bit;
RXCRS: inout bit;
RXD0: linkage bit;
RXD1: in bit;
RXDAT: inout bit;
RXPOL_L: out bit;
R_W_L: in bit;
SCLK: in bit;
SF_BD: out bit;
SLEEP_L: in bit;
SRD: out bit;
SRDCLK: inout bit;
STDCLK: inout bit;
TCK: in bit;
TC_L: in bit;
TDI: in bit;
TDO: out bit;
TDTREQ_L: out bit;
TMS: in bit;
TXD0: linkage bit;
TXD1: out bit;
TXDAT0: out bit;
TXDAT1: inout bit;
TXEN_L: inout bit;
TXP0: linkage bit;
132
Am79C940
TXP1: out bit;
XTAL1: in bit;
XTAL2: linkage bit
);
use STD_1149_1_1990.all;
attribute PIN_MAP of AM79C940 : entity is PHYSICAL_PIN_MAP;
constant PLCC_PACKAGE: PIN_MAP_STRING:=
"ADD:(49,50,51,52,53)," &
"AVDD1:66," &
"AVDD2:71," &
"AVDD3:78," &
"AVDD4:83," &
"AVSS1:73," &
"AVSS2:75," &
"BE0_L:44," &
"BE1_L:45," &
"CI0:81," &
"CI1:82," &
"CLSN:9," &
"CS_L:55," &
"DBUS:(21,23,24,25,26,28,29,30,31,32," &
"33,34,35,36,38,39)," &
"DI0:79," &
"DI1:80," &
"DO0:76," &
"DO1:77," &
"DTV_L:42," &
"DVDD1:63," &
"DVDD2:84," &
"DVDDN:37," &
"DVDDP:18," &
"DVSS1:61," &
"DVSS2:3," &
"DVSSN1:22," &
"DVSSN2:27," &
"DVSSN3:40," &
Am79C940
133
"DVSSP:6," &
"DXRCV_L:1," &
"EAM_R_L:13," &
"EDSEL:2," &
"EOF_L:41," &
"FDS_L:43," &
"INTR_L:19," &
"LNKST_L:57," &
"RDTREQ_L:48," &
"RESET_L:16," &
"RXCRS:11," &
"RXD0:64," &
"RXD1:65," &
"RXDAT:10," &
"RXPOL_L:56," &
"R_W_L:54," &
"SCLK:46," &
"SF_BD:15," &
"SLEEP_L:17," &
"SRD:14," &
"SRDCLK:12," &
"STDCLK:7," &
"TCK:60," &
"TC_L:20," &
"TDI:62," &
"TDO:58," &
"TDTREQ_L:47," &
"TMS:59," &
"TXD0:68," &
"TXD1:70," &
"TXDAT0:5," &
"TXDAT1:4," &
"TXEN_L:8," &
"TXP0:67," &
"TXP1:69," &
"XTAL1:72," &
"XTAL2:74";
constant PQFP_PACKAGE: PIN_MAP_STRING:=
134
Am79C940
"ADD:(46,47,48,49,50)," &
"AVDD1:67," &
"AVDD2:72," &
"AVDD3:83," &
"AVDD4:88," &
"AVSS1:74," &
"AVSS2:79," &
"BE0_L:41," &
"BE1_L:42," &
"CI0:86," &
"CI1:87," &
"CLSN:98," &
"CS_L:56," &
"DBUS:(14,16,17,18,19,21,22,23,24,25," &
"29,31,32,33,35,36)," &
"DI0:84," &
"DI1:85," &
"DO0:81," &
"DO1:82," &
"DTV_L:39," &
"DVDD1:64," &
"DVDD2:89," &
"DVDDN:34," &
"DVDDP:11," &
"DVSS1:62," &
"DVSS2:92," &
"DVSSN1:15," &
"DVSSN2:20," &
"DVSSN3:37," &
"DVSSP:95," &
"DXRCV_L:90," &
"EAM_R_L:6," &
"EDSEL:91," &
"EOF_L:38," &
"FDS_L:40," &
"INTR_L:12," &
"LNKST_L:58," &
"RDTREQ_L:45," &
"RESET_L:9," &
Am79C940
135
"RXCRS:100," &
"RXD0:65," &
"RXD1:66," &
"RXDAT:99," &
"RXPOL_L:57," &
"R_W_L:55," &
"SCLK:43," &
"SF_BD:8," &
"SLEEP_L:10," &
"SRD:7," &
"SRDCLK:5," &
"STDCLK:96," &
"TCK:61," &
"TC_L:13," &
"TDI:63," &
"TDO:59," &
"TDTREQ_L:44," &
"TMS:60," &
"TXD0:69," &
"TXD1:71," &
"TXDAT0:94," &
"TXDAT1:93," &
"TXEN_L:97," &
"TXP0:68," &
"TXP1:70," &
"XTAL1:73," &
"XTAL2:75";
attribute TAP_SCAN_IN
of TDI : signal is true;
attribute TAP_SCAN_OUT
of TDO : signal is true;
attribute TAP_SCAN_MODE
of TMS : signal is true;
attribute TAP_SCAN_CLOCK of TCK : signal is (1.00e+07, BOTH);
attribute INSTRUCTION_LENGTH of AM79C940 : entity is 4;
attribute INSTRUCTION_OPCODE of AM79C940 : entity is
"BYPASS ( 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110," &
" 1111)," &
"EXTEST ( 0000)," &
"IDCODE ( 0001)," &
136
Am79C940
"SAMPLE ( 0010)," &
"SELFTST ( 0101)," &
"SETBYP ( 0100)," &
"TRIBYP ( 0011)" ;
attribute INSTRUCTION_CAPTURE of AM79C940 : entity is "0001";
attribute INSTRUCTION_DISABLE of AM79C940 : entity is "TRIBYP";
attribute INSTRUCTION_PRIVATE of AM79C940 : entity is
" SELFTST";
attribute IDCODE_REGISTER of AM79C940 : entity is
"0011" &-- version
"1001010000000000" &-- part number
"00000000001" &-- manufacturer’s id
"1";-- required by standard
attribute REGISTER_ACCESS of AM79C940 : entity is
"BYPASS ( BYPASS, SETBYP, TRIBYP)," &
"BOUNDARY ( EXTEST, SAMPLE, SELFTST)," &
"IDCODE ( IDCODE)";
attribute BOUNDARY_CELLS of AM79C940 : entity is
" BC_1, BC_4";
attribute BOUNDARY_LENGTH of AM79C940 : entity is 99;
attribute BOUNDARY_REGISTER of AM79C940 : entity is
"
0 (BC_1, *, control, 0)," &
"
1 (BC_1, LNKST_L, output3, X, 0, 0, Weak1)," &
"
2 (BC_1, RXPOL_L, output3, X, 0, 0, Weak1)," &
"
3 (BC_1, CS_L, input, 1)," &
"
4 (BC_1, R_W_L, input, 1)," &
"
5 (BC_1, ADD(4), input, 0)," &
"
6 (BC_1, ADD(3), input, 0)," &
"
7 (BC_1, ADD(2), input, 0)," &
"
8 (BC_1, ADD(1), input, 0)," &
"
9 (BC_1, ADD(0), input, 0)," &
Am79C940
137
"
10 (BC_1, *, control, 0)," &
"
11 (BC_1, RDTREQ_L, output3, X, 10, 0, Z)," &
"
12 (BC_1, TDTREQ_L, output3, X, 10, 0, Z)," &
"
13 (BC_4, SCLK, clock, 1)," &
"
14 (BC_1, BE1_L, input, 1)," &
"
15 (BC_1, BE0_L, input, 1)," &
"
16 (BC_1, FDS_L, input, 1)," &
"
17 (BC_1, *, control, 0)," &
"
18 (BC_1, DTV_L, output3, X, 17, 0, Z)," &
"
19 (BC_1, *, control, 0)," &
"
20 (BC_1, EOF_L, output3, X, 19, 0, Z)," &
"
21 (BC_1, EOF_L, input, 1)," &
"
22 (BC_1, *, control, 0)," &
"
23 (BC_1, DBUS(15), output3, X, 22, 0, Z)," &
"
24 (BC_1, DBUS(15), input, 0)," &
"
25 (BC_1, DBUS(14), output3, X, 22, 0, Z)," &
"
26 (BC_1, DBUS(14), input, 0)," &
"
27 (BC_1, DBUS(13), output3, X, 22, 0, Z)," &
"
28 (BC_1, DBUS(13), input, 0)," &
"
29 (BC_1, DBUS(12), output3, X, 22, 0, Z)," &
"
30 (BC_1, DBUS(12), input, 0)," &
"
31 (BC_1, DBUS(11), output3, X, 22, 0, Z)," &
"
32 (BC_1, DBUS(11), input, 0)," &
"
33 (BC_1, DBUS(10), output3, X, 22, 0, Z)," &
"
34 (BC_1, DBUS(10), input, 0)," &
"
35 (BC_1, *, control, 0)," &
"
36 (BC_1, DBUS(9), output3, X, 35, 0, Z)," &
"
37 (BC_1, DBUS(9), input, 0)," &
"
38 (BC_1, DBUS(8), output3, X, 35, 0, Z)," &
"
39 (BC_1, DBUS(8), input, 0)," &
"
40 (BC_1, DBUS(7), output3, X, 35, 0, Z)," &
"
41 (BC_1, DBUS(7), input, 0)," &
"
42 (BC_1, DBUS(6), output3, X, 35, 0, Z)," &
"
43 (BC_1, DBUS(6), input, 0)," &
"
44 (BC_1, DBUS(5), output3, X, 35, 0, Z)," &
"
45 (BC_1, DBUS(5), input, 0)," &
"
46 (BC_1, DBUS(4), output3, X, 35, 0, Z)," &
"
47 (BC_1, DBUS(4), input, 0)," &
"
48 (BC_1, DBUS(3), output3, X, 35, 0, Z)," &
138
Am79C940
"
49 (BC_1, DBUS(3), input, 0)," &
"
50 (BC_1, DBUS(2), output3, X, 35, 0, Z)," &
"
51 (BC_1, DBUS(2), input, 0)," &
"
52 (BC_1, DBUS(1), output3, X, 35, 0, Z)," &
"
53 (BC_1, DBUS(1), input, 0)," &
"
54 (BC_1, DBUS(0), output3, X, 35, 0, Z)," &
"
55 (BC_1, DBUS(0), input, 0)," &
"
56 (BC_1, TC_L, input, 1)," &
"
57 (BC_1, *, control, 0)," &
"
58 (BC_1, INTR_L, output3, 1, 57, 0, Weak1)," &
"
59 (BC_1, SLEEP_L, input, 1)," &
"
60 (BC_1, RESET_L, input, 1)," &
"
61 (BC_1, *, control, 0)," &
"
62 (BC_1, SF_BD, output3, X, 61, 0, Z)," &
"
63 (BC_1, SRD, output3, X, 61, 0, Z)," &
"
64 (BC_1, EAM_R_L, input, 0)," &
"
65 (BC_1, *, control, 0)," &
"
66 (BC_1, SRDCLK, output3, X, 65, 0, Z)," &
"
67 (BC_1, SRDCLK, input, 0)," &
"
68 (BC_1, *, control, 0)," &
"
69 (BC_1, RXCRS, output3, X, 68, 0, Z)," &
"
70 (BC_1, RXCRS, input, 0)," &
"
71 (BC_1, *, control, 0)," &
"
72 (BC_1, RXDAT, output3, X, 71, 0, Z)," &
"
73 (BC_1, RXDAT, input, 0)," &
"
74 (BC_1, *, control, 0)," &
"
75 (BC_1, CLSN, output3, X, 74, 0, Z)," &
"
76 (BC_1, CLSN, input, 0)," &
"
77 (BC_1, *, control, 0)," &
"
78 (BC_1, TXEN_L, output3, X, 77, 0, Z)," &
"
79 (BC_1, TXEN_L, input, 0)," &
"
80 (BC_1, *, control, 0)," &
"
81 (BC_1, STDCLK, output3, X, 80, 0, Z)," &
"
82 (BC_1, STDCLK, input, 0)," &
"
83 (BC_1, *, control, 0)," &
"
84 (BC_1, TXDAT0, output3, X, 83, 0, Z)," &
"
85 (BC_1, TXDAT1, output3, X, 83, 0, Z)," &
"
86 (BC_1, TXDAT1, input, 1)," &
"
87 (BC_1, EDSEL, input, 1)," &
Am79C940
139
"
88 (BC_1, *, control, 0)," &
"
89 (BC_1, DXRCV_L, output3, X, 88, 0, Z)," &
"
90 (BC_4, XTAL1, clock, 0)," &
"
91 (BC_1, RXD1, input, 1)," &
"
92 (BC_1, *, control, 0)," &
"
93 (BC_1, TXP1, output3, X, 92, 0, Z)," &
"
94 (BC_1, TXD1, output3, X, 92, 0, Z)," &
"
95 (BC_1, *, control, 0)," &
"
96 (BC_1, DO1, output3, X, 95, 0, Z)," &
"
97 (BC_4, DI1, input, 1)," &
"
98 (BC_4, CI1, input, 1)";
end AM79C940;
140
Am79C940
APPENDIX C
Am79C940 MACE Rev C0 Silicon
Errata
The items below are the known errata for Rev C0 silicon. Rev C0 is the production silicon.
The enclosed is a list of known errata’s encountered with the MACE Rev C0 device. Each of these errata’s is provided with description, implication, and workaround (if possible). Where the errata was published in a previous errata list, is so noted. Other than those listed exceptions below that have not been fixed, the MACE Rev C0
production device is fully functional.
The "Description" section of the errata gives a brief description of the problem. The "Implication" section of the
errata describes the effects of the problem in a system configuration. The "Workaround" section of the errata describes methods to minimize the system effects. The “Status” section of the errata describes when and how the
problem will be corrected.
Current package marking for this revision: Line 1: <Logo>
Line 2: Am79C940BKC (Assuming package is PQFP)
Line 3: <Date Code>
Line 4: (c) 1992 AMD
Value of CHIPID register for this revision: CHIPID[15:00] = 3940h
1) Receive Fragment Frame Treated as a New Packet Even After Receive FIFO Overflows:
Description: The MACE device continues to receive the remains of a long packet even after the receive FIFO
overflows. If this data stream has the ’Start of Frame’ (SFD) bit pattern "10101011" (and no "00" bit pattern
before the "SFD" pattern) and the destination address field of the packet matches the station address after
the SFD bit pattern, or if the MACE device is in promiscuous mode, the remaining portion of the long packet
will be received and treated by the MACE device as a new packet even though the receive status will show
an FCS error.
Implication: There is no impact of any kind if the receive FIFO overflow is not permitted by the system design.
The likelihood of such an occurrence of the above conditions is extremely remote. Should this condition occur,
this will impact performance only in products using the “cut-through” method. This is because the "cutthrough" method will not look at the FCS field, which would indicate an error in the packet received.
Workaround: Check for FCS error after the packet is received.
Status: No current plan to fix this item.
2) In Low Latency Receive Mode, Loses Synchronization When Connected to a Coaxial Transceiver via the
AUI Port:
Description: In low latency receive mode, the MACE device loses synchronization when connected to a coaxial (10BASE2) transceiver. The problem occurs when connecting the MACE to a coaxial transceiver via the
AUI interface, and at the same time the MACE device is programmed into low latency receive mode. When
a collision occurs in the media and if MACE device continues to receive data, after the collision is ended, the
MACE device loses synchronization.
Implication: No performance impact to the MACE device if the 10BASE-T port is used instead of a 10BASE2
coaxial transceiver connected to the AUI port of the MACE device.
Workaround: This condition is being validated at this time. In the meantime, it is recommended that if the
product is to be used in a network topology where a 10BASE2 coaxial transceiver is connected to the AUI
port, care must be exercised to avoid using the MACE device in low latency receiver mode.
Am79C940
141
Status: No current plan to fix this item.
3) Flashing LED for Link Status:
Description: When TMAU receiver is receiving negative polarity link pulse, and the automatic polarity correction algorithm (DAPC bit in PHY Configuration Control Register) is disabled, link test state machine will loop
between ’link fail’ and ’link pass’ state causing the Link Status LED to flash.
Implication: There is no impact to system performance. However, the Link Status LED flashing may cause
an erroneous interpretation by the user.
Workaround: There is no workaround.
Status: No current plan to fix this item.
4) Incorrect Runt Packet Count in Low Latency Receive Mode:
Description: In Low Latency Receive mode, the MACE Runt Packet count is incremented when the receive
packet is less than 12 bytes. The correct runt packet count should always be incremented when the receive
packet is less than 64 bytes.
Implication: There is no impact on system performance if the runt packet count is not being utilized by the
system.
Workaround: This condition is being validated at this time. Therefore, a workaround for this is to be determined.
5) Device Failure at 1.25 MHz System Clock:
Description: MACE device does not function reliability at system clock speed of less than 5MHz due to architecture constraints.
Implication: There is no performance impact since the serial clock is still running at the IEEE specified
10MHz.
Workarounds:
1. Avoid operating the MACE device at speeds of less than 5MHz.
2. Send one packet at a time. Essentially, write one packet to the transmit FIFO, let the Mace device
transmit that packet, wait for the transmit complete interrupt, before writing another packet to the
transmit FIFO.
Status: No current plan to fix this item.
6) False BABL errors generated:
Description: The MACE device will intermittenly give BABL error indications when the network traffic has
frames equal to or greater than 1518 bytes.
Implication: False BABL errors on the receiving station can be passed up to the upper layer software if MACE
device is just coming out of deferral and the multi-purpose counter used to count the number of bytes recevied
reaches 1518 at the same time. If the network is heavily loaded with full-size frames, then the probability of
a false BABL error is high.
Workaround: There are two possible workarounds.
1. If the user has no intention to transmit frames larger than 1518 bytes, then the BABL bit may be
masked to ignore babble errors. In this case the false babble error will not cause an interrupt, nor will
it be passed to the higher level software.
2. Check to see if the device is transmitting in ISR (Interrupt Service Routine), which is induced by the
BABL error. The BCRs which control the LED settings can be programmed to indicate a transmit activity, assuming the interrupt latency is not longer than one mininum IFG (inter-frame gap) time.
142
Am79C940
If (ISR_LATENCY < 9.6 us)
True_bable_err = BABL * ( TINT + XMT_LED)
{ i.e. False_bable_err = ~ (BABL * ( TINT + XMT_LED))}
else
Cannot tell if the BABL error is true or false just by reading BABL, TINT,
XMT_LED bits in ISR.
Status: No current plan to fix this item.
Am79C940
143
144
Am79C940