EXAR XR16M2750

XR16M2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
JUNE 2007
REV. P1.0.0
GENERAL DESCRIPTION
The XR16M27501 (M2750) is a high performance
dual universal asynchronous receiver and transmitter
(UART) with 64 byte TX and RX FIFOs. The device
operates from 1.62 to 3.6 volts and is pin-to-pin
compatible to Exar’s ST16C2550 and XR16V2750.
The M2750 register set is identical to the XR16V2750
and is compatible to the ST16C2550 and the
XR16C2850 enhanced features. It supports the
Exar’s enhanced features of programmable FIFO
trigger level and FIFO level counters, automatic
hardware (RTS/CTS) and software flow control,
automatic RS-485 half duplex direction control output
and a complete modem interface. Onboard registers
provide the user with operational status and data
error flags. An internal loopback capability allows
system diagnostics. Independent programmable
baud rate generators are provided in each channel to
select data rates up to 8 Mbps at 3.3 Volt and 8X
sampling clock. The M2750 is available in 48-pin
TQFP and 32-pin QFN packages.
FEATURES
• 1.62 to 3.6 Volt Operation
• Pin-to-pin compatible to Exar’s XR16V2750 and
TI’s TL16C752B in the 48-TQFP package
• Two independent UART channels
■
Register set compatible to XR16V2750
■
Data rate of up to 8 Mbps at 3.3 V, 6.25 Mbps
at 2.5 V and 4 Mbps at 1.8 V with 8X sampling
rate
■
Fractional Baud Rate Generator
■
Transmit and Receive FIFOs of 64 bytes
■
Programmable TX and RX FIFO Trigger Levels
■
Transmit and Receive FIFO Level Counters
■
Automatic Hardware (RTS/CTS) Flow Control
■
Selectable Auto RTS Flow Control Hysteresis
■
Automatic Software (Xon/Xoff) Flow Control
■
Automatic RS-485 Half-duplex
Control Output via RTS#
NOTE: 1 Covered by U.S. Patent #5,649,122
■
Wireless Infrared (IrDA 1.0) Encoder/Decoder
APPLICATIONS
■
Automatic sleep mode
• Portable Appliances
• Telecommunication Network Routers
• Ethernet Network Routers
• Cellular Data Devices
• Factory Automation and Process Controls
■
Full modem interface
Direction
• Device Identification and Revision
• Crystal oscillator (up to 32MHz) or external clock
(upto 64MHz) input
• 48-TQFP and 32-QFN packages
FIGURE 1. XR16M2750 BLOCK DIAGRAM
1.62 to 3.6 Volt VCC
A2:A0
D7:D0
GND
IOR#
IOW#
UART Channel A
CSA#
CSB#
INTA
INTB
TXRDYA#
TXRDYB#
RXRDYA#
RXRDYB#
Reset
UART
Regs
8-bit Data
Bus
Interface
BRG
64 Byte TX FIFO
TX & RX
IR
ENDEC
TXA, RXA, DTRA#,
DSRA#, RTSA#,
DTSA#, CDA#, RIA#,
OP2A#
64 Byte RX FIFO
UART Channel B
(same as Channel A)
Crystal Osc/Buffer
TXB, RXB, DTRB#,
DSRB#, RTSB#,
CTSB#, CDB#, RIB#,
OP2B#
XTAL1
XTAL2
2750BLK
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
CDA#
DSRA#
CTSA#
NC
38
37
RIA#
41
39
VCC
42
40
D0
TXRDYA#
43
D1
45
44
D3
D2
46
D4
48
47
FIGURE 2. PIN OUT ASSIGNMENT
RESET
D5
1
36
D6
2
35
D7
3
34
DTRA#
RXB
4
33
RTSA#
RXA
5
32
OP2A#
XR16M2750
48-pin TQFP
TXRDYB# 6
DTRB#
31
RXRDYA#
INTA
TXA
7
30
TXB
23
24
CTSB#
NC
CTSA#
25
22
RTSB#
VCC
26
21
RIB#
D0
27
19
20
IOR#
DSRB#
D1
28
18
RXRDYB#
29 D2
17
16
32 D5
GND
NC
CDB#
25
31 D4
A2
NC 12
30 D3
A1
26
15
27
CSB# 11
IOW#
CSA# 10
13
A0
14
INTB
28
XTAL2
29
XTAL1
8
OP2B# 9
D6
1
24
RESET
D7
2
23
RTSA#
RXB
3
22
INTA
RXA
4
TXA
5
XR16M2750
32-pin QFN
21
INTB
20
A0
NC
CTSB# 16
NC
RTSB# 15
17
IOR# 14
CSB#
GND 13
A2
8
IOW# 12
A1
18
XTAL2 11
19
7
XTAL1 10
6
9
TXB
CSA#
ORDERING INFORMATION
PART NUMBER
PACKAGE
OPERATING TEMPERATURE RANGE
DEVICE STATUS
XR16M2750IL32
32-pin QFN
-40°C to +85°C
Active
XR16M2750IM48
48-Lead TQFP
-40°C to +85°C
Active
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PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
PIN DESCRIPTIONS
Pin Description
NAME
32-QFN
PIN #
48-TQFP
PIN #
TYPE
DESCRIPTION
Address data lines [2:0]. These 3 address lines select one of the internal registers in UART channel A/B during a data bus transaction.
DATA BUS INTERFACE
A2
A1
A0
18
19
20
26
27
28
I
D7
D6
D5
D4
D3
D2
D1
D0
2
1
32
31
30
29
28
27
3
2
1
48
47
46
45
44
I/O
IOR#
14
19
I
Input/Output Read Strobe (active low). The falling edge instigates an
internal read cycle and retrieves the data byte from an internal register
pointed to by the address lines [A2:A0]. The data byte is placed on the
data bus to allow the host processor to read it on the rising edge.
IOW#
12
15
I
Input/Output Write Strobe (active low). The falling edge instigates an
internal write cycle and the rising edge transfers the data byte on the
data bus to an internal register pointed by the address lines.
CSA#
7
10
I
UART channel A select (active low) to enable UART channel A in the
device for data bus operation.
CSB#
8
11
I
UART channel B select (active low) to enable UART channel B in the
device for data bus operation.
INTA
22
30
O
UART channel A Interrupt output. The output state is defined by the
user through the software setting of MCR[3]. INTA is set to the active
mode and OP2A# output LOW when MCR[3] is set to a logic 1. INTA is
set to the three state mode and OP2A# output HIGH when MCR[3] is
set to a logic 0 (default). See MCR[3].
INTB
21
29
O
UART channel B Interrupt output. The output state is defined by the
user through the software setting of MCR[3]. INTB is set to the active
mode and OP2B# output LOW when MCR[3] is set to a logic 1. INTB is
set to the three state mode and OP2B# output HIGH when MCR[3] is
set to a logic 0 (default). See MCR[3].
TXRDYA#
-
43
O
UART channel A Transmitter Ready (active low). The output provides
the TX FIFO/THR status for transmit channel A. See Table 2. If it is not
used, leave it unconnected.
RXRDYA#
-
31
O
UART channel A Receiver Ready (active low). This output provides the
RX FIFO/RHR status for receive channel A. See Table 2. If it is not
used, leave it unconnected.
TXRDYB#
-
6
O
UART channel B Transmitter Ready (active low). The output provides
the TX FIFO/THR status for transmit channel B. See Table 3. If it is not
used, leave it unconnected.
Data bus lines [7:0] (bidirectional).
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PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
Pin Description
NAME
32-QFN
PIN #
48-TQFP
PIN #
TYPE
DESCRIPTION
RXRDYB#
-
18
O
UART channel B Receiver Ready (active low). This output provides the
RX FIFO/RHR status for receive channel B. See Table 2. If it is not
used, leave it unconnected.
MODEM OR SERIAL I/O INTERFACE
TXA
5
7
O
UART channel A Transmit Data or infrared encoder data. Standard
transmit and receive interface is enabled when MCR[6] = 0. In this
mode, the TX signal will be HIGH during reset or idle (no data). Infrared
IrDA transmit and receive interface is enabled when MCR[6] = 1. In the
Infrared mode, the inactive state (no data) for the Infrared encoder/
decoder interface is LOW. If it is not used, leave it unconnected.
RXA
4
5
I
UART channel A Receive Data or infrared receive data. Normal receive
data input must idle HIGH. The infrared receiver pulses typically idles at
LOW but can be inverted by software control prior going in to the
decoder, see MCR[6] and FCTR[2]. If this pin is not used, tie it to VCC
or pull it high via a 100k ohm resistor.
RTSA#
23
33
O
UART channel A Request-to-Send (active low) or general purpose output. This output must be asserted prior to using auto RTS flow control,
see EFR[6], MCR[1], FCTR[1:0], EMSR[5:4] and IER[6]. For auto
RS485 half-duplex direction control, see FCTR[3] and EMSR[3].
CTSA#
25
38
I
UART channel A Clear-to-Send (active low) or general purpose input.
It can be used for auto CTS flow control, see EFR[7], and IER[7]. This
input should be connected to VCC when not used.
DTRA#
-
34
O
UART channel A Data-Terminal-Ready (active low) or general purpose
output. If it is not used, leave it unconnected.
DSRA#
-
39
I
UART channel A Data-Set-Ready (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
CDA#
-
40
I
UART channel A Carrier-Detect (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
RIA#
-
41
I
UART channel A Ring-Indicator (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
OP2A#
-
32
O
Output Port 2 Channel A - The output state is defined by the user and
through the software setting of MCR[3]. INTA is set to the active mode
and OP2A# output LOW when MCR[3] is set to a logic 1. INTA is set to
the three state mode and OP2A# output HIGH when MCR[3] is set to a
logic 0. See MCR[3]. If INTA is used, this output should not be used as
a general output else it will disturb the INTA output functionality.
TXB
6
8
O
UART channel B Transmit Data or infrared encoder data. Standard
transmit and receive interface is enabled when MCR[6] = 0. In this
mode, the TX signal will be HIGH during reset or idle (no data). Infrared
IrDA transmit and receive interface is enabled when MCR[6] = 1. In the
Infrared mode, the inactive state (no data) for the Infrared encoder/
decoder interface is LOW. If it is not used, leave it unconnected.
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PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
Pin Description
NAME
32-QFN
PIN #
48-TQFP
PIN #
TYPE
DESCRIPTION
RXB
3
4
I
UART channel B Receive Data or infrared receive data. Normal receive
data input must idle HIGH. The infrared receiver pulses typically idles at
logic 0 but can be inverted by software control prior going in to the
decoder, see MCR[6] and FCTR[2]. If this pin is not used, tie it to VCC
or pull it high via a 100k ohm resistor.
RTSB#
15
22
O
UART channel B Request-to-Send (active low) or general purpose output. This port must be asserted prior to using auto RTS flow control,
see EFR[6], MCR[1], FCTR[1:0], EMSR[5:4] and IER[6]. For auto
RS485 half-duplex direction control, see FCTR[3] and EMSR[3].
CTSB#
16
23
I
UART channel B Clear-to-Send (active low) or general purpose input.
It can be used for auto CTS flow control, see EFR[7], and IER[7]. This
input should be connected to VCC when not used.
DTRB#
-
35
O
UART channel B Data-Terminal-Ready (active low) or general purpose
output. If it is not used, leave it unconnected.
DSRB#
-
20
I
UART channel B Data-Set-Ready (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
CDB#
-
16
I
UART channel B Carrier-Detect (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
RIB#
-
21
I
UART channel B Ring-Indicator (active low) or general purpose input.
This input should be connected to VCC when not used. This input has
no effect on the UART.
OP2B#
-
9
O
Output Port 2 Channel B - The output state is defined by the user and
through the software setting of MCR[3]. INTB is set to the active mode
and OP2B# output LOW when MCR[3] is set to a logic 1. INTB is set to
the three state mode and OP2B# output HIGH when MCR[3] is set to a
logic 0. See MCR[3]. If INTB is used, this output should not be used as
a general output else it will disturb the INTB output functionality.
ANCILLARY SIGNALS
XTAL1
10
13
I
Crystal or external clock input.
XTAL2
11
14
O
Crystal or buffered clock output.
RESET
24
36
I
Reset (active high) - A longer than 40 ns HIGH pulse on this pin will
reset the internal registers and all outputs. The UART transmitter output
will be held HIGH, the receiver input will be ignored and outputs are
reset during reset period (see Table 16).
VCC
26
42
Pwr
1.62V to 3.6V power supply.
GND
13
17
Pwr
Power supply common, ground.
GND
Center Pad
N/A
Pwr
The center pad on the backside of the 32-QFN package is metallic and
should be connected to GND on the PCB. The thermal pad size on the
PCB should be the approximate size of this center pad and should be
solder mask defined. The solder mask opening should be at least
0.0025" inwards from the edge of the PCB thermal pad.
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PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
Pin Description
NAME
32-QFN
PIN #
48-TQFP
PIN #
N.C.
9, 17
12, 24, 25,
37
TYPE
DESCRIPTION
No Connection.
Pin type: I=Input, O=Output, I/O= Input/output, OD=Output Open Drain.
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PRELIMINARY
REV. P1.0.0
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
1.0 PRODUCT DESCRIPTION
The XR16M2750 (M2750) integrates the functions of 2 enhanced 16C550 Universal Asynchronous Receiver
and Transmitter (UART). Each UART is independently controlled having its own set of device configuration
registers. The configuration registers set is 16550 UART compatible for control, status and data transfer.
Additionally, each UART channel has 64-bytes of transmit and receive FIFOs, automatic RTS/CTS hardware
flow control with hysteresis control, automatic Xon/Xoff and special character software flow control,
programmable transmit and receive FIFO trigger levels, FIFO level counters, infrared encoder and decoder
(IrDA ver 1.0), programmable fractional baud rate generator with a prescaler of divide by 1 or 4, and data rate
up to 8 Mbps with 8X sampling clock rate or 4 Mbps in the 16X rate. The XR16M2750 is a 1.62 to 3.6V device.
The M2750 is fabricated with an advanced CMOS process.
Enhanced Features
The M2750 DUART provides a solution that supports 64 bytes of transmit and receive FIFO memory, instead
of 16 bytes in the ST16C2550 or one byte in the ST16C2450. The M2750 is designed to work with low supply
voltage and high performance data communication systems, that require fast data processing time. Increased
performance is realized in the M2750 by the larger transmit and receive FIFOs, FIFO trigger level control, FIFO
level counters and automatic flow control mechanism. This allows the external processor to handle more
networking tasks within a given time. For example, the ST16C2550 with a 16 byte FIFO, unloads 16 bytes of
receive data in 1.53 ms (This example uses a character length of 11 bits, including start/stop bits at 115.2
Kbps). This means the external CPU will have to service the receive FIFO at 1.53 ms intervals. However with
the 64 byte FIFO in the M2750, the data buffer will not require unloading/loading for 6.1 ms. This increases the
service interval giving the external CPU additional time for other applications and reducing the overall UART
interrupt servicing time. In addition, the programmable FIFO level trigger interrupt and automatic hardware/
software flow control is uniquely provided for maximum data throughput performance especially when
operating in a multi-channel system. The combination of the above greatly reduces the CPU’s bandwidth
requirement, increases performance, and reduces power consumption.
The M2750 supports a half-duplex output direction control signaling pin, RTS# A/B, to enable and disable the
external RS-485 transceiver operation. It automatically switches the logic state of the output pin to the receive
state after the last stop-bit of the last character has been shifted out of the transmitter. After receiving, the logic
state of the output pin switches back to the transmit state when a data byte is loaded in the transmitter. The
auto RS-485 direction control pin is not activated after reset. To activate the direction control function, user has
to set FCTR Bit-3 to “1”. This pin is normally high for receive state, low for transmit state.
Data Rate
The M2750 is capable of operation up to 4 Mbps at 3.3V with 16X internal sampling clock rate and 8 Mbps at
3.3V with 8X sampling clock rate. The device can operate with an external 32 MHz crystal at 2.5V on pins
XTAL1 and XTAL2, or external clock source of up to 64 MHz on XTAL1 pin. With a typical crystal of 14.7456
MHz and through a software option, the user can set the prescaler bit for data rates of up to 1.84 Mbps.
The rich feature set of the M2750 is available through the internal registers. Automatic hardware/software flow
control, selectable transmit and receive FIFO trigger levels, selectable TX and RX baud rates, infrared
encoder/decoder interface, modem interface controls, and a sleep mode are all standard features.
Following a power on reset or an external reset, the M2750 is software compatible with previous generation of
UARTs, 16C450, 16C550 and 16C650A as well as the 16C850.
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PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
2.0 FUNCTIONAL DESCRIPTIONS
2.1
CPU Interface
The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and
write transactions. The M2750 data interface supports the Intel compatible types of CPUs and it is compatible
to the industry standard 16C550 UART. No clock (oscillator nor external clock) is required to operate a data
bus transaction. Each bus cycle is asynchronous using CS#, IOR# and IOW# signals. Both UART channels
share the same data bus for host operations. The data bus interconnections are shown in Figure 3.
FIGURE 3. XR16M2750 DATA BUS INTERCONNECTIONS
D0
D1
D2
D3
D4
D5
D6
D7
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A0
A1
VCC
TXA
RXA
UART
Channel A
IOW#
IOW#
CSA#
CSB#
UART_INTA
INTA
UART_INTB
INTB
TXRDYA#
TXRDYA#
RXRDYA#
RXRDYA#
TXRDYB#
TXRDYB#
RXRDYB#
CTSA#
DSRA#
Serial Interface of
RS-232, RS-485
RIA#
OP2A#
IOR#
UART_CSA#
UART_CSB#
DTRA#
RTSA#
CDA#
A2
IOR#
VCC
TXB
RXB
UART
Channel B
DTRB#
RTSB#
CTSB#
DSRB#
Serial Interface of
RS-232, RS-485
CDB#
RIB#
OP2B#
RXRDYB#
UART_RESET
RESET
GND
2750int
2.2
Device Reset
The RESET input resets the internal registers and the serial interface outputs in both channels to their default
state (see Table 16). An active high pulse of longer than 40 ns duration will be required to activate the reset
function in the device.
2.3
Device Identification and Revision
The XR16M2750 provides a Device Identification code and a Device Revision code to distinguish the part from
other devices and revisions. To read the identification code from the part, it is required to set the baud rate
generator registers DLL and DLM both to 0x00 (DLD = 0xXX). Now reading the content of the DLM will provide
0x0A for the XR16M2750 and reading the content of DLL will provide the revision of the part; for example, a
reading of 0x01 means revision A.
2.4
Channel A and B Selection
The UART provides the user with the capability to bi-directionally transfer information between an external
CPU and an external serial communication device. A LOW signal on the chip select pins, CSA# or CSB#,
allows the user to select UART channel A or B to configure, send transmit data and/or unload receive data to/
from the UART. Selecting both UARTs can be useful during power up initialization to write to the same internal
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PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
registers, but do not attempt to read from both uarts simultaneously. Individual channel select functions are
shown in Table 1.
TABLE 1: CHANNEL A AND B SELECT
2.5
CSA#
CSB#
FUNCTION
1
1
UART de-selected
0
1
Channel A selected
1
0
Channel B selected
0
0
Channel A and B selected
Channel A and B Internal Registers
Each UART channel in the M2750 has a set of enhanced registers for control, monitoring and data loading and
unloading. The configuration register set is compatible to those already available in the standard single
16C550 and dual ST16C2550. These registers function as data holding registers (THR/RHR), interrupt status
and control registers (ISR/IER), a FIFO control register (FCR), receive line status and control registers (LSR/
LCR), modem status and control registers (MSR/MCR), programmable data rate (clock) divisor registers (DLL/
DLM/DLD), and a user accessible Scratchpad Register (SPR).
Beyond the general 16C2550 features and capabilities, the M2750 offers enhanced feature registers (EMSR,
FLVL, EFR, Xon/Xoff 1, Xon/Xoff 2, FCTR, TRG, FC) that provide automatic RTS and CTS hardware flow
control, Xon/Xoff software flow control, automatic RS-485 half-duplex direction output enable/disable, FIFO
trigger level control, and FIFO level counters. All the register functions are discussed in full detail later in
“Section 3.0, UART Internal Registers” on page 22.
2.6
DMA Mode
The device does not support direct memory access. The DMA Mode (a legacy term) in this document doesn’t
mean “direct memory access” but refers to data block transfer operation. The DMA mode affects the state of
the RXRDY# A/B and TXRDY# A/B output pins. The transmit and receive FIFO trigger levels provide additional
flexibility to the user for block mode operation. The LSR bits 5-6 provide an indication when the transmitter is
empty or has an empty location(s) for more data. The user can optionally operate the transmit and receive
FIFO in the DMA mode (FCR bit-3=1). When the transmit and receive FIFO are enabled and the DMA mode is
disabled (FCR bit-3 = 0), the M2750 is placed in single-character mode for data transmit or receive operation.
When DMA mode is enabled (FCR bit-3 = 1), the user takes advantage of block mode operation by loading or
unloading the FIFO in a block sequence determined by the programmed trigger level. In this mode, the M2750
sets the TXRDY# pin when the transmit FIFO becomes full, and sets the RXRDY# pin when the receive FIFO
becomes empty. The following table shows their behavior. Also see Figures 17 through 22.
TABLE 2: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE
PINS
FCR BIT-0=0
(FIFO DISABLED)
FCR BIT-0=1 (FIFO ENABLED)
FCR Bit-3 = 0
(DMA Mode Disabled)
RXRDY# A/B LOW = 1 byte.
HIGH = no data.
LOW = at least 1 byte in FIFO.
HIGH = FIFO empty.
TXRDY# A/B LOW = THR empty. LOW = FIFO empty.
HIGH = byte in THR. HIGH = at least 1 byte in FIFO.
9
FCR Bit-3 = 1
(DMA Mode Enabled)
HIGH to LOW transition when FIFO reaches the
trigger level, or time-out occurs.
LOW to HIGH transition when FIFO empties.
LOW = FIFO has at least 1 empty location.
HIGH = FIFO is full.
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.7
REV. P1.0.0
INTA and INTB Outputs
The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup.
Table 3 and 4 summarize the operating behavior for the transmitter and receiver. Also see Figures 17
through 22.
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER
Auto RS485
Mode
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1 (FIFO ENABLED)
INTA/B Pin
NO
LOW = a byte in THR
HIGH = THR empty
LOW = FIFO above trigger level
HIGH = FIFO below trigger level or FIFO empty
INTA/B Pin
YES
LOW = a byte in THR
HIGH = transmitter empty
LOW = FIFO above trigger level
HIGH = FIFO below trigger level or transmitter empty
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER
FCR BIT-0 = 0
(FIFO DISABLED)
INTA/B Pin
2.8
LOW = no data
HIGH = 1 byte
FCR BIT-0 = 1
(FIFO ENABLED)
LOW = FIFO below trigger level
HIGH = FIFO above trigger level
Crystal Oscillator or External Clock Input
The M2750 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections in the
device. The CPU data bus does not require this clock for bus operation. The crystal oscillator provides a
system clock to the Baud Rate Generators (BRG) section found in each of the UART. XTAL1 is the input to the
oscillator or external clock buffer input with XTAL2 pin being the output. For programming details, see
““Section 2.9, Programmable Baud Rate Generator with Fractional Divisor” on page 11.”
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS
XTAL1
XTAL2
R2
500 ΚΩ − 1 ΜΩ
Y1
C1
22-47 pF
C2
22-47 pF
10
R1
0-120 Ω
(Optional)
1.8432 MHz
to
24 MHz
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant,
fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100 ppm frequency
tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4). The programmable Baud
Rate Generator is capable of operating with a crystal oscillator frequency of up to 32 MHz at 2.5V. However,
with an external clock input on XTAL1 pin, it can extend its operation up to 64 MHz (8 Mbps serial data rate) at
3.3V with an 8X sampling rate. For further reading on the oscillator circuit please see the Application Note
DAN108 on the EXAR web site at http://www.exar.com.
2.9
Programmable Baud Rate Generator with Fractional Divisor
Each UART has its own Baud Rate Generator (BRG) with a prescaler for the transmitter and receiver. The
prescaler is controlled by a software bit in the MCR register. The MCR register bit-7 sets the prescaler to divide
the input crystal or external clock by 1 or 4. The output of the prescaler clocks to the BRG. The BRG further
divides this clock by a programmable divisor between 1 and (216 - 0.0625) in increments of 0.0625 (1/16) to
obtain a 16X or 8X sampling clock of the serial data rate. The sampling clock is used by the transmitter for data
bit shifting and receiver for data sampling. The BRG divisor (DLL, DLM and DLD registers) defaults to the value
of ’1’ (DLL = 0x01, DLM = 0x00 and DLD = 0x00) upon reset. Therefore, the BRG must be programmed during
initialization to the operating data rate. The DLL and DLM registers provide the integer part of the divisor and
the DLD register provides the fractional part of the dvisior. Only the four lower bits of the DLD are implemented
and they are used to select a value from 0 (for setting 0000) to 0.9375 or 15/16 (for setting 1111). Programming
the Baud Rate Generator Registers DLL, DLM and DLD provides the capability for selecting the operating data
rate. Table 5 shows the standard data rates available with a 24MHz crystal or external clock at 16X clock rate.
If the pre-scaler is used (MCR bit-7 = 1), the output data rate will be 4 times less than that shown in Table 5. At
8X sampling rate, these data rates would double. Also, when using 8X sampling mode, please note that the bittime will have a jitter (+/- 1/16) whenever the DLD is non-zero and is an odd number. When using a nonstandard data rate crystal or external clock, the divisor value can be calculated with the following equation(s):
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler) / (serial data rate x 16), with 16X mode EMSR[7] = 1
Required Divisor (decimal) = (XTAL1 clock frequency / prescaler / (serial data rate x 8), with 8X mode EMSR[7] = 0
The closest divisor that is obtainable in the M2750 can be calculated using the following formula:
ROUND( (Required Divisor - TRUNC(Required Divisor) )*16)/16 + TRUNC(Required Divisor), where
DLM = TRUNC(Required Divisor) >> 8
DLL = TRUNC(Required Divisor) & 0xFF
DLD = ROUND( (Required Divisor-TRUNC(Required Divisor) )*16)
In the formulas above, please note that:
TRUNC (N) = Integer Part of N. For example, TRUNC (5.6) = 5.
ROUND (N) = N rounded towards the closest integer. For example, ROUND (7.3) = 7 and ROUND (9.9) = 10.
A >> B indicates right shifting the value ’A’ by ’B’ number of bits. For example, 0x78A3 >> 8 = 0x0078.
11
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 5. BAUD RATE GENERATOR
To Other
Channel
DLL, DLM and DLD
Registers
MCR Bit-7=0
(default)
Prescaler
Divide by 1
Crystal
Osc/
Buffer
XTAL1
XTAL2
Fractional Baud
Rate Generator
Logic
Prescaler
Divide by 4
16X or 8X
Sampling
Rate Clock
to Transmitter
and Receiver
MCR Bit-7=1
TABLE 5: TYPICAL DATA RATES WITH A 24 MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING
Required
Output Data
Rate
DIVISOR FOR
16x Clock
(Decimal)
DIVISOR
OBTAINABLE IN
M2750
DLM PROGRAM
VALUE (HEX)
DLL PROGRAM
VALUE (HEX)
DLD PROGRAM
VALUE (HEX)
DATA ERROR
RATE (%)
400
3750
3750
E
A6
0
0
2400
625
625
2
71
0
0
4800
312.5
312 8/16
1
38
8
0
9600
156.25
156 4/16
0
9C
4
0
10000
150
150
0
96
0
0
19200
78.125
78 2/16
0
4E
2
0
25000
60
60
0
3C
0
0
28800
52.0833
52 1/16
0
34
1
0.04
38400
39.0625
39 1/16
0
27
1
0
50000
30
30
0
1E
0
0
57600
26.0417
26 1/16
0
1A
1
0.08
75000
20
20
0
14
0
0
100000
15
15
0
F
0
0
115200
13.0208
13
0
D
0
0.16
153600
9.7656
9 12/16
0
9
C
0.16
200000
7.5
7 8/16
0
7
8
0
225000
6.6667
6 11/16
0
6
B
0.31
230400
6.5104
6 8/16
0
6
8
0.16
250000
6
6
0
6
0
0
300000
5
5
0
5
0
0
400000
3.75
3 12/16
0
3
C
0
460800
3.2552
3 4/16
0
3
4
0.16
500000
3
3
0
3
0
0
750000
2
2
0
2
0
0
921600
1.6276
1 10/16
0
1
A
0.16
1000000
1.5
1 8/16
0
1
8
0
12
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
2.10
XR16M2750
Transmitter
The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 64 bytes of FIFO which
includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X/8X internal
clock. A bit time is 16 (8) clock periods (see EMSR bit-7). The transmitter sends the start-bit followed by the
number of data bits, inserts the proper parity-bit if enabled, and adds the stop-bit(s). The status of the FIFO and
TSR are reported in the Line Status Register (LSR bit-5 and bit-6).
2.10.1
Transmit Holding Register (THR) - Write Only
The transmit holding register is an 8-bit register providing a data interface to the host processor. The host
writes transmit data byte to the THR to be converted into a serial data stream including start-bit, data bits,
parity-bit and stop-bit(s). The least-significant-bit (Bit-0) becomes first data bit to go out. The THR is the input
register to the transmit FIFO of 64 bytes when FIFO operation is enabled by FCR bit-0. Every time a write
operation is made to the THR, the FIFO data pointer is automatically bumped to the next sequential data
location.
2.10.2
Transmitter Operation in non-FIFO Mode
The host loads transmit data to THR one character at a time. The THR empty flag (LSR bit-5) is set when the
data byte is transferred to TSR. THR flag can generate a transmit empty interrupt (ISR bit-1) when it is enabled
by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty.
FIGURE 6. TRANSMITTER OPERATION IN NON-FIFO MODE
Data
Byte
16X or 8X
Clock
(EMSR Bit-7)
Transmit
Holding
Register
(THR)
THR Interrupt (ISR bit-1)
Enabled by IER bit-1
Transmit Shift Register (TSR)
M
S
B
L
S
B
TXNOFIFO1
2.10.3
Transmitter Operation in FIFO Mode
The host may fill the transmit FIFO with up to 64 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the
amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by
IER bit-1. The TSR flag (LSR bit-6) is set when TSR/FIFO becomes empty.
13
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 7. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE
Transmit
Data Byte
Transm it
FIFO
THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
empty. FIFO is Enabled by FCR
bit-0=1
Auto CTS Flow Control (CTS# pin)
Flow Control Characters
(Xoff1/2 and Xon1/2 Reg.
Auto Software Flow Control
16X or 8X Clock
(EMSR bit-7)
Transm it Data Shift Register
(TSR)
T XF IF O 1
2.11
Receiver
The receiver section contains an 8-bit Receive Shift Register (RSR) and 64 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X/8X clock (EMSR bit-7) for timing. It verifies
and validates every bit on the incoming character in the middle of each data bit. On the falling edge of a start or
false start bit, an internal receiver counter starts counting at the 16X/8X clock rate. After 8 clocks (or 4 if 8X) the
start bit period should be at the center of the start bit. At this time the start bit is sampled and if it is still a logic
0 it is validated. Evaluating the start bit in this manner prevents the receiver from assembling a false character.
The rest of the data bits and stop bits are sampled and validated in this same manner to prevent false framing.
If there were any error(s), they are reported in the LSR register bits 2-4. Upon unloading the receive data byte
from RHR, the receive FIFO pointer is bumped and the error tags are immediately updated to reflect the status
of the data byte in RHR register. RHR can generate a receive data ready interrupt upon receiving a character
or delay until it reaches the FIFO trigger level. Furthermore, data delivery to the host is guaranteed by a
receive data ready time-out interrupt when data is not received for 4 word lengths as defined by LCR[1:0] plus
12 bits time. This is equivalent to 3.7-4.6 character times. The RHR interrupt is enabled by IER bit-0.
2.11.1
Receive Holding Register (RHR) - Read-Only
The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift
Register. It provides the receive data interface to the host processor. The RHR register is part of the receive
FIFO of 64 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When
the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the
RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data
byte are immediately updated in the LSR bits 2-4.
14
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 8. RECEIVER OPERATION IN NON-FIFO MODE
16X or 8X C lock
(E M S R bit-7)
R eceive D ata S hift
R egister (R S R )
E rror
T ags in
LS R bits
4:2
R eceive
D ata B yte
and E rrors
D ata B it
V alidation
R eceive D ata
H olding R egister
(R H R )
R e ce ive D a ta C h a ra cte rs
R H R Interrupt (IS R bit-2)
R X F IF O 1
FIGURE 9. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
16X or 8X Clock
(EMSR bit-7)
Receive Data Shift
Register (RSR)
Data Bit
Validation
Example
- :RX FIFO trigger level selected at 16
bytes
(See Note Below)
Data falls to
RTS# re-asserts when data falls below the flow
8
control trigger level to restart remote transmitter.
Error Tags
(64-sets)
64 bytes by 11-bit
wide
FIFO
Receive
Data FIFO
Enable by EFR bit-6=1, MCR bit-1.
FIFO
Trigger=16
Error Tags in
LSR bits 4:2
Data fills to
24
Receive Data
Byte and Errors
Receive Data Characters
RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
Receive
Data
RXFIFO1
NOTE: Table-B selected as Trigger Table for Figure 9 (Table 10).
15
XR16M2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.12
REV. P1.0.0
Auto RTS (Hardware) Flow Control
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see Figure 10):
• Enable auto RTS flow control using EFR bit-6.
• The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).
If using the Auto RTS interrupt:
• Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1.
2.13
Auto RTS Hysteresis
The M2750 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with
the XR16C850, ST16C650A and ST16C550 family of UARTs. With the Auto RTS function enabled, an interrupt
is generated when the receive FIFO reaches the programmed RX trigger level. The RTS# pin will not be forced
HIGH (RTS off) until the receive FIFO reaches the upper limit of the hysteresis level. The RTS# pin will return
LOW after the RX FIFO is unloaded to the lower limit of the hysteresis level. Under the above described
conditions, the M2750 will continue to accept data until the receive FIFO gets full. The Auto RTS function is
initiated when the RTS# output pin is asserted LOW (RTS On). Table 13 shows the complete details for the
Auto RTS# Hysteresis levels. Please note that this table is for programmable trigger levels only (Table D). The
hysteresis values for Tables A-C are the next higher and next lower trigger levels in the corresponding table.
2.14
Auto CTS Flow Control
Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is
monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific
application requirement (see Figure 10):
• Enable auto CTS flow control using EFR bit-7.
If using the Auto CTS interrupt:
• Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the
CTS# pin is de-asserted (HIGH): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as
the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is reasserted (LOW), indicating more data may be sent.
16
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 10. AUTO RTS AND CTS FLOW CONTROL OPERATION
Local UART
UARTA
Remote UART
UARTB
RXA
Receiver FIFO
Trigger Reached
RTSA#
Auto RTS
Trigger Level
Receiver FIFO
Trigger Reached
RTSB#
Assert RTS# to Begin
Transmission
1
ON
Auto RTS
Trigger Level
10
OFF
ON
7
2
CTSB#
Auto CTS
Monitor
RXB
CTSA#
Auto CTS
Monitor
Transmitter
CTSB#
TXA
Transmitter
RTSA#
TXB
ON
3
8
OFF
6
Suspend
11
ON
TXB
Data Starts
4
Restart
9
RXA FIFO
INTA
(RXA FIFO
Interrupt)
Receive
RX FIFO
Data
Trigger Level
5
RTS High
Threshold
RTS Low
Threshold
12
RX FIFO
Trigger Level
RTSCTS1
The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of
remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO
(4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and continues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA
monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows
(7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its transmit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9),
UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until
next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB
with RTSB# and CTSA# controlling the data flow.
17
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.15
REV. P1.0.0
Auto Xon/Xoff (Software) Flow Control
When software flow control is enabled (See Table 15), the M2750 compares one or two sequential receive
data characters with the programmed Xon or Xoff-1,2 character value(s). If receive character(s) (RX) match the
programmed values, the M2750 will halt transmission (TX) as soon as the current character has completed
transmission. When a match occurs, the Xoff (if enabled via IER bit-5) flag will be set and the interrupt output
pin will be activated. Following a suspension due to a match of the Xoff character, the M2750 will monitor the
receive data stream for a match to the Xon-1,2 character. If a match is found, the M2750 will resume operation
and clear the flags (ISR bit-4).
Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to 0x00. Following reset the user can
write any Xon/Xoff value desired for software flow control. Different conditions can be set to detect Xon/Xoff
characters (See Table 15) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are
selected, the M2750 compares two consecutive receive characters with two software flow control 8-bit values
(Xon1, Xon2, Xoff1, Xoff2) and controls TX transmissions accordingly. Under the above described flow control
mechanisms, flow control characters are not placed (stacked) in the user accessible RX data buffer or FIFO.
In the event that the receive buffer is overfilling and flow control needs to be executed, the M2750
automatically sends an Xoff message via the serial TX output to the remote modem. The M2750 sends the
Xoff-1,2 characters two-character times (= time taken to send two characters at the programmed baud rate)
after the receive FIFO crosses the programmed trigger level (for all trigger tables). To clear this condition, the
M2750 will transmit the programmed Xon-1,2 characters as soon as receive FIFO is less than one trigger level
below the programmed trigger level (for Trigger Tables A, B, and C) or when receive FIFO is less than the
trigger level minus the hysteresis value (for Trigger Table D). This hysteresis value is the same as the Auto
RTS Hysteresis value in Table 14. Table 6 below explains this when Trigger Table-B (See Table 10) is
selected.
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL
RX TRIGGER LEVEL
INT PIN ACTIVATION
XOFF CHARACTER(S) SENT
(CHARACTERS IN RX FIFO)
XON CHARACTER(S) SENT
(CHARACTERS IN RX FIFO)
8
8
8*
0
16
16
16*
8
24
24
24*
16
28
28
28*
24
* After the trigger level is reached, an xoff character is sent after a short span of time (= time required to send 2
characters); for example, after 2.083ms has elapsed for 9600 baud and 10-bit word length setting.
2.16
Special Character Detect
A special character detect feature is provided to detect an 8-bit character when bit-5 is set in the Enhanced
Feature Register (EFR). When this character (Xoff2) is detected, it will be placed in the FIFO along with normal
incoming RX data.
The M2750 compares each incoming receive character with Xoff-2 data. If a match exists, the received data
will be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the
Internal Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of
bits is dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of
character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also
determines the number of bits that will be used for the special character comparison.
2.17
Auto RS485 Half-duplex Control
The auto RS485 half-duplex direction control changes the behavior of the transmitter when enabled by FCTR
bit-3. By default, it de-asserts RTS# (HIGH) output following the last stop bit of the last character that has been
transmitted. This helps in turning around the transceiver to receive the remote station’s response. When the
host is ready to transmit next polling data packet again, it only has to load data bytes to the transmit FIFO. The
18
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
transmitter automatically re-asserts RTS# (LOW) output prior to sending the data. The RS485 half-duplex
direction control output can be inverted by enabling EMSR bit-3.
2.18
Infrared Mode
The M2750 UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data
Association) version 1.0. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of a bit
wide HIGH-pulse for each “0” bit in the transmit data stream. This signal encoding reduces the on-time of the
infrared LED, hence reduces the power consumption. See Figure 11 below.
The infrared encoder and decoder are enabled by setting MCR register bit-6 to a ‘1’. When the infrared feature
is enabled, the transmit data output, TX, idles at logic zero level. Likewise, the RX input assumes an idle level
of logic zero from a reset and power up, see Figure 11.
Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin.
Each time it senses a light pulse, it returns a logic 1 to the data bit stream. However, this is not true with some
infrared modules on the market which indicate a logic 0 by a light pulse. So the M2750 has a provision to invert
the input polarity to accommodate this. In this case user can enable FCTR bit-2 to invert the input signal.
FIGURE 11. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING
TX Data
0
Stop
Start
Character
Data Bits
1
0
1
0
1
0
1
1
0
Transmit
IR Pulse
(TX Pin)
1/2 Bit Time
Bit Time
3/16 Bit Time
IrEncoder-1
Receive
IR Pulse
(RX pin)
Bit Time
1/16 Clock Delay
1
0
1
0
0
Data Bits
1 1
0
1
Stop
0
Start
RX Data
Character
IRdecoder-
19
XR16M2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
2.19
REV. P1.0.0
Sleep Mode with Auto Wake-Up
The M2750 supports low voltage system designs, hence, a sleep mode is included to reduce its power
consumption when the chip is not actively used.
All of these conditions must be satisfied for the M2750 to enter sleep mode:
■
no interrupts pending for both channels of the M2750 (ISR bit-0 = 1)
■
sleep mode of both channels are enabled (IER bit-4 = 1)
■
modem inputs are not toggling (MSR bits 0-3 = 0)
■
RX input pins are idling HIGH
The M2750 stops its crystal oscillator to conserve power in the sleep mode. User can check the XTAL2 pin for
no clock output as an indication that the device has entered the sleep mode.
The M2750 resumes normal operation by any of the following:
■
a receive data start bit transition (HIGH to LOW)
■
a data byte is loaded to the transmitter, THR or FIFO
■
a change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI#
If the M2750 is awakened by any one of the above conditions, it will return to the sleep mode automatically
after all interrupting conditions have been serviced and cleared. If the M2750 is awakened by the modem
inputs, a read to the MSR is required to reset the modem inputs. In any case, the sleep mode will not be
entered while an interrupt is pending from channel A or B. The M2750 will stay in the sleep mode of operation
until it is disabled by setting IER bit-4 to a logic 0.
If the address lines, data bus lines, IOW#, IOR#, CSA#, CSB#, and modem input lines remain steady when the
M2750 is in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical
Characteristics on page 41. If the input lines are floating or are toggling while the M2750 is in sleep mode, the
current can be up to 100 times more. If any of those signals are toggling or floating, then an external buffer
would be required to keep the address, data and control lines steady to achieve the low current. As an
alternative, please refer to the XR16V2751 which is pin-to-pin and software compatible with the M2750 but with
(some additional pins and) the PowerSave feature that eliminates any unnecessary external buffer.
A word of caution: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the
first few receive characters may be lost. The number of characters lost during the restart also depends on your
operating data rate. More characters are lost when operating at higher data rate. Also, it is important to keep
RX A/B inputs idling HIGH or “marking” condition during sleep mode to avoid receiving a “break” condition
upon the restart. This may occur when the external interface transceivers (RS-232, RS-485 or another type)
are also put to sleep mode and cannot maintain the “marking” condition. To avoid this, the designer can use a
47k-100k ohm pull-up resistor on the RXA and RXB pins.
20
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
2.20
XR16M2750
Internal Loopback
The M2750 UART provides an internal loopback capability for system diagnostic purposes. The internal
loopback mode is enabled by setting MCR register bit-4 to logic 1. All regular UART functions operate normally.
Figure 12 shows how the modem port signals are re-configured. Transmit data from the transmit shift register
output is internally routed to the receive shift register input allowing the system to receive the same data that it
was sending. The TX, RTS# and DTR# pins are held while the CTS#, DSR# CD# and RI# inputs are ignored.
Caution: the RX input pin must be held HIGH during loopback test else upon exiting the loopback test the
UART may detect and report a false “break” signal. Also, Auto RTS/CTS flow control is not supported during
internal loopback.
FIGURE 12. INTERNAL LOOP BACK IN CHANNEL A AND B
VCC
TXA/TXB
Transmit Shift Register
(THR/FIFO)
Receive Shift Register
(RHR/FIFO)
RXA/RXB
VCC
RTSA#/RTSB#
RTS#
Modem / General Purpose Control Logic
Internal Data Bus Lines and Control Signals
MCR bit-4=1
CTS#
CTSA#/CTSB#
VCC
DTRA#/DTRB#
DTR#
DSR#
DSRA#/DSRB#
OP1#
RI#
RIA#/RIB#
VCC
OP2A#/OP2B#
OP2#
CD#
CDA#/CDB#
21
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
3.0 UART INTERNAL REGISTERS
Each of the UART channel in the M2750 has its own set of configuration registers selected by address lines
A0, A1 and A2 with CSA# or CSB# selecting the channel. The complete register set is shown on Table 7 and
Table 8.
TABLE 7: UART CHANNEL A AND B UART INTERNAL REGISTERS
ADDRESSES
A2 A1 A0
REGISTER
READ/WRITE
COMMENTS
LCR[7] = 0
16C550 COMPATIBLE REGISTERS
0
0 0
RHR - Receive Holding Register
THR - Transmit Holding Register
Read-only
Write-only
0
0 0
DLL - Divisor LSB
Read/Write
0
0 1
DLM - Divisor MSB
Read/Write
0
1 0
DLD - Divisor Fractional
Read/Write
LCR[7] = 1, LCR ≠ 0xBF,
EFR[4] = 1
0
0 0
DREV - Device Revision Code
Read-only
0
0 1
DVID - Device Identification Code
Read-only
DLL, DLM = 0x00,
LCR[7] = 1, LCR ≠ 0xBF
0
0 1
IER - Interrupt Enable Register
Read/Write
LCR[7] = 0
0
1 0
ISR - Interrupt Status Register
FCR - FIFO Control Register
Read-only
Write-only
LCR ≠ 0xBF
0
1 1
LCR - Line Control Register
Read/Write
1
0 0
MCR - Modem Control Register
Read/Write
1
0 1
LSR - Line Status Register
Read-only
1
1 0
MSR - Modem Status Register
Read-only
1
1 1
SPR - Scratch Pad Register
Read/Write
1
1 1
FLVL - RX/TX FIFO Level Counter Register
Read-only
1
1 1
EMSR - Enhanced Mode Select Register
Write-only
LCR[7] = 1, LCR ≠ 0xBF
LCR ≠ 0xBF
LCR ≠ 0xBF, FCTR[6] = 0
LCR ≠ 0xBF, FCTR[6] = 1
ENHANCED REGISTERS
0
0 0
TRG - RX/TX FIFO Trigger Level Register
FC - RX/TX FIFO Level Counter Register
Write-only
Read-only
0
0 1
FCTR - Feature Control Register
Read/Write
0
1 0
EFR - Enhanced Function Register
Read/Write
1
0 0
Xon-1 - Xon Character 1
Read/Write
1
0 1
Xon-2 - Xon Character 2
Read/Write
1
1 0
Xoff-1 - Xoff Character 1
Read/Write
1
1 1
Xoff-2 - Xoff Character 2
Read/Write
22
LCR = 0xBF
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
.
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS
A2-A0
REG
NAME
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
COMMENT
16C550 Compatible Registers
000
RHR
RD
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
000
THR
WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
001
IER
RD/WR
0/
0/
0/
0/
CTS Int. RTS Int.
Enable Enable
Xoff Int.
Enable
Sleep
Mode
Enable
FIFOs
FIFOs
Enabled Enabled
0/
0/
INT
Source
Bit-5
INT
Source
Bit-4
0/
0/
010
010
ISR
FCR
RD
WR
RX FIFO RX FIFO
Trigger Trigger
TX FIFO TX FIFO
Trigger Trigger
011
LCR
RD/WR
Divisor
Enable
Set TX
Break
Set Parity
100
MCR
RD/WR
0/
0/
0/
BRG
Prescaler
Even
Parity
Modem RX Line
TX
RX
Stat. Int.
Stat.
Empty
Data
Enable
Int.
Int
Int.
Enable Enable Enable
INT
Source
Bit-3
INT
INT
INT
Source Source Source
Bit-2
Bit-1
Bit-0
DMA
Mode
Enable
TX
FIFO
Reset
Parity
Enable
Stop
Bits
LCR ≠ 0xBF
RX
FIFO
Reset
FIFOs
Enable
Word
Word
Length Length
Bit-1
Bit-0
Internal OP2#/INT Rsrvd RTS# DTR#
Lopback Output (OP1#) Output Output
IR Mode XonAny Enable
Enable
Control Control
ENable
101
LSR
RD
RX FIFO
Global
Error
THR &
TSR
Empty
THR
Empty
RX
Break
RX Framing Error
RX
Parity
Error
RX
Overrun
Error
RX
Data
Ready
110
MSR
RD
CD#
Input
RI#
Input
DSR#
Input
CTS#
Input
Delta
CD#
Delta
RI#
Delta
DSR#
Delta
CTS#
111
SPR
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
111
EMSR
WR
16X
Sampling
Rate
Mode
LSR
Error
Interrupt.
Imd/Dly#
Auto
RTS
Hyst.
bit-3
Auto
RTS
Hyst.
bit-2
Auto
RS485
Output
Inversion
Rsrvd
Rx/Tx
FIFO
Count
Rx/Tx
FIFO
Count
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
111
FLVL
RD
LCR[7]=0
23
LCR ≠ 0xBF
LCR ≠ 0xBF
FCTR[6]=0
LCR ≠ 0xBF
FCTR[6]=1
Bit-1
Bit-0
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1
ADDRESS
A2-A0
REG
NAME
READ/
WRITE
BIT-7
BIT-6
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
COMMENT
LCR[7]=1
LCR ≠ 0xBF
Baud Rate Generator Divisor
000
DLL
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
001
DLM
RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
010
DLD
RD/WR
0
0
0
0
Bit-3
Bit-2
Bit-1
Bit-0
LCR[7]=1
LCR ≠ 0xBF
EFR[4] = 1
000
DREV
RD
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
001
DVID
RD
0
0
0
0
1
0
1
0
LCR[7]=1
LCR ≠ 0xBF
DLL=0x00
DLM=0x00
Enhanced Registers
000
TRG
WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
000
FC
RD
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
RX/TX
Mode
SCPAD
Swap
Trig
Table
Bit-1
Trig
Table
Bit-0
Auto
RS485
Direction
Control
RX IR
Input
Inv.
Auto
RTS
Hyst
Bit-1
Auto
RTS
Hyst
Bit-0
Auto
CTS
Enable
Auto
RTS
Enable
Special
Char
Select
Enable
Software
Flow
Cntl
Bit-2
Software
Flow
Cntl
Bit-1
Software
Flow
Cntl
Bit-0
DLD
Software
Flow
Cntl
Bit-3
001
010
FCTR RD/WR
EFR
RD/WR
IER [7:4],
ISR [5:4],
FCR[5:4],
MCR[7:5],
100
XON1 RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
101
XON2 RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
110
XOFF1 RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
111
XOFF2 RD/WR
Bit-7
Bit-6
Bit-5
Bit-4
Bit-3
Bit-2
Bit-1
Bit-0
LCR=0XBF
4.0 INTERNAL REGISTER DESCRIPTIONS
4.1
Receive Holding Register (RHR) - Read- Only
SEE”RECEIVER” ON PAGE 14.
4.2
Transmit Holding Register (THR) - Write-Only
SEE”TRANSMITTER” ON PAGE 13.
4.3
Interrupt Enable Register (IER) - Read/Write
The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status
and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR).
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4.3.1
XR16M2750
IER versus Receive FIFO Interrupt Mode Operation
When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts
(see ISR bits 2 and 3) status will reflect the following:
A. The receive data available interrupts are issued to the host when the FIFO has reached the programmed
trigger level. It will be cleared when the FIFO drops below the programmed trigger level.
B. FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register
status bit and the interrupt will be cleared when the FIFO drops below the trigger level.
C. The receive data ready bit (LSR BIT-0) is set as soon as a character is transferred from the shift register to
the receive FIFO. It is reset when the FIFO is empty.
4.3.2
IER versus Receive/Transmit FIFO Polled Mode Operation
When FCR BIT-0 equals a logic 1 for FIFO enable; resetting IER bits 0-3 enables the XR16M2750 in the FIFO
polled mode of operation. Since the receiver and transmitter have separate bits in the LSR either or both can
be used in the polled mode by selecting respective transmit or receive control bit(s).
A. LSR BIT-0 indicates there is data in RHR or RX FIFO.
B. LSR BIT-1 indicates an overrun error has occurred and that data in the FIFO may not be valid.
C. LSR BIT 2-4 provides the type of receive data errors encountered for the data byte in RHR, if any.
D. LSR BIT-5 indicates THR is empty.
E. LSR BIT-6 indicates when both the transmit FIFO and TSR are empty.
F. LSR BIT-7 indicates a data error in at least one character in the RX FIFO.
IER[0]: RHR Interrupt Enable
The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode or when
the receive FIFO has reached the programmed trigger level in the FIFO mode.
• Logic 0 = Disable the receive data ready interrupt (default).
• Logic 1 = Enable the receiver data ready interrupt.
IER[1]: THR Interrupt Enable
This bit enables the Transmit Ready interrupt which is issued whenever the THR becomes empty in the nonFIFO mode or when data in the FIFO falls below the programmed trigger level in the FIFO mode. If the THR is
empty when this bit is enabled, an interrupt will be generated.
• Logic 0 = Disable Transmit Ready interrupt (default).
• Logic 1 = Enable Transmit Ready interrupt.
IER[2]: Receive Line Status Interrupt Enable
If any of the LSR register bits 1, 2, 3 or 4 is a logic 1, it will generate an interrupt to inform the host controller
about the error status of the current data byte in FIFO. LSR bit-1 generates an interrupt immediately when the
character has been received. LSR bits 2-4 generate an interrupt when the character with errors is read out of
the FIFO (default). Instead, LSR bits 2-4 can be programmed to generate an interrupt immediately, by setting
EMSR bit-6 to a logic 1.
• Logic 0 = Disable the receiver line status interrupt (default).
• Logic 1 = Enable the receiver line status interrupt.
IER[3]: Modem Status Interrupt Enable
• Logic 0 = Disable the modem status register interrupt (default).
• Logic 1 = Enable the modem status register interrupt.
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IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1)
• Logic 0 = Disable Sleep Mode (default).
• Logic 1 = Enable Sleep Mode. See Sleep Mode section for further details.
IER[5]: Xoff Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the software flow control, receive Xoff interrupt (default).
• Logic 1 = Enable the receive Xoff interrupt. See Software Flow Control section for details.
IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the RTS# interrupt (default).
• Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition
from low to high.
IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1)
• Logic 0 = Disable the CTS# interrupt (default).
• Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from
low to high.
4.4
Interrupt Status Register (ISR) - Read-Only
The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The
Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the
ISR will give the user the current highest pending interrupt level to be serviced, others are queued up to be
serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt
Source Table, Table 9, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources
associated with each of these interrupt levels.
4.4.1
Interrupt Generation:
• LSR is by any of the LSR bits 1, 2, 3 and 4.
• RXRDY is by RX trigger level.
• RXRDY Time-out is by a 4-char plus 12 bits delay timer.
• TXRDY is by TX trigger level or TX FIFO empty (or transmitter empty in auto RS-485 control).
• MSR is by any of the MSR bits 0, 1, 2 and 3.
• Receive Xoff/Special character is by detection of a Xoff or Special character.
• CTS# is when its transmitter toggles the input pin (from LOW to HIGH) during auto CTS flow control.
• RTS# is when its receiver toggles the output pin (from LOW to HIGH) during auto RTS flow control.
4.4.2
Interrupt Clearing:
• LSR interrupt is cleared by a read to the LSR register.
• RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level.
• RXRDY Time-out interrupt is cleared by reading RHR.
• TXRDY interrupt is cleared by a read to the ISR register or writing to THR.
• MSR interrupt is cleared by a read to the MSR register.
• Xoff interrupt is cleared by a read to ISR or when Xon character(s) is received.
• Special character interrupt is cleared by a read to ISR or after the next character is received.
• RTS# and CTS# flow control interrupts are cleared by a read to the MSR register.
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REV. P1.0.0
]
TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY
ISR REGISTER STATUS BITS
SOURCE OF INTERRUPT
LEVEL
BIT-5
BIT-4
BIT-3
BIT-2
BIT-1
BIT-0
1
0
0
0
1
1
0
LSR (Receiver Line Status Register)
2
0
0
1
1
0
0
RXRDY (Receive Data Time-out)
3
0
0
0
1
0
0
RXRDY (Received Data Ready)
4
0
0
0
0
1
0
TXRDY (Transmit Ready)
5
0
0
0
0
0
0
MSR (Modem Status Register)
6
0
1
0
0
0
0
RXRDY (Received Xoff or Special character)
7
1
0
0
0
0
0
CTS#, RTS# change of state
-
0
0
0
0
0
1
None (default)
ISR[0]: Interrupt Status
• Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.
• Logic 1 = No interrupt pending (default condition).
ISR[3:1]: Interrupt Status
These bits indicate the source for a pending interrupt at interrupt priority levels (See Interrupt Source Table 9).
ISR[4]: Xoff/Xon or Special Character Interrupt Status
This bit is set when EFR[4] = 1 and IER[5] = 1. ISR bit-4 indicates that the receiver detected a data match of
the Xoff character(s). If this is an Xoff interrupt, it can be cleared by a read to the ISR. If it is a special character
interrupt, it can be cleared by reading ISR or it will automatically clear after the next character received.
ISR[5]: RTS#/CTS# Interrupt Status
This bit is enabled when EFR[4] = 1. ISR bit-5 indicates that the CTS# or RTS# has been de-asserted.
ISR[7:6]: FIFO Enable Status
These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are
enabled.
4.5
FIFO Control Register (FCR) - Write-Only
This register is used to enable the FIFOs, clear the FIFOs, set the transmit/receive FIFO trigger levels, and
select the DMA mode. The DMA, and FIFO modes are defined as follows:
FCR[0]: TX and RX FIFO Enable
• Logic 0 = Disable the transmit and receive FIFO (default).
• Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are
written or they will not be programmed.
FCR[1]: RX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
• Logic 0 = No receive FIFO reset (default)
• Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (the receive shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO.
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FCR[2]: TX FIFO Reset
This bit is only active when FCR bit-0 is a ‘1’.
• Logic 0 = No transmit FIFO reset (default).
• Logic 1 = Reset the transmit FIFO pointers and FIFO level counter logic (the transmit shift register is not
cleared or altered). This bit will return to a logic 0 after resetting the FIFO.
FCR[3]: DMA Mode Select
Controls the behavior of the TXRDY# and RXRDY# pins. See DMA operation section for details.
• Logic 0 = Normal Operation (default).
• Logic 1 = DMA Mode.
FCR[5:4]: Transmit FIFO Trigger Select (requires EFR bit-4=1)
(logic 0 = default, TX trigger level = 1)
These 2 bits set the trigger level for the transmit FIFO. The UART will issue a transmit interrupt when the
number of characters in the FIFO falls below the selected trigger level, or when it gets empty in case that the
FIFO did not get filled over the trigger level on last re-load. Table 10 below shows the selections. EFR bit-4
must be set to ‘1’ before these bits can be accessed. Note that the receiver and the transmitter cannot use
different trigger tables. Whichever selection is made last applies to both the RX and TX side.
FCR[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
The FCTR Bits 5-4 are associated with these 2 bits. These 2 bits are used to set the trigger level for the receive
FIFO. The UART will issue a receive interrupt when the number of the characters in the FIFO crosses the
trigger level. Table 10 shows the complete selections. Note that the receiver and the transmitter cannot use
different trigger tables. Whichever selection is made last applies to both the RX and TX side.
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REV. P1.0.0
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION
TRIGGER
TABLE
FCTR
BIT-5
FCTR
BIT-4
Table-A
0
0
FCR
BIT-7
FCR
BIT-6
0
0
1
1
Table-B
0
Table-D
4.6
1
1
1
0
0
X
X
COMPATIBILITY
16C550, 16C2550,
16C2552, 16C554,
16C580
16
8
24
30
16C650A
8
16
32
56
16C654
8
16
24
28
0
0
1
1
0
1
0
1
TRANSMIT
TRIGGER
LEVEL
1 (default)
0
1
0
1
0
1
0
1
0
0
1
1
RECEIVE
TRIGGER LEVEL
1 (default)
4
8
14
0
0
1
1
0
1
FCR
BIT-4
0
1
0
1
0
0
1
1
Table-C
FCR
BIT-5
0
1
0
1
8
16
56
60
X
X
Programmable Programmable 16L2752, 16C2850,
16C2852, 16C850,
via TRG
via TRG
16C854, 16C864
register.
register.
FCTR[7] = 0.
FCTR[7] = 1.
Line Control Register (LCR) - Read/Write
The Line Control Register is used to specify the asynchronous data communication format. The word or
character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this
register.
LCR[1:0]: TX and RX Word Length Select
These two bits specify the word length to be transmitted or received.
BIT-1
BIT-0
WORD LENGTH
0
0
5 (default)
0
1
6
1
0
7
1
1
8
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LCR[2]: TX and RX Stop-bit Length Select
The length of stop bit is specified by this bit in conjunction with the programmed word length.
LENGTH
STOP BIT LENGTH
(BIT TIME(S))
0
5,6,7,8
1 (default)
1
5
1-1/2
1
6,7,8
2
BIT-2
WORD
LCR[3]: TX and RX Parity Select
Parity or no parity can be selected via this bit. The parity bit is a simple way used in communications for data
integrity check. See Table 11 for parity selection summary below.
• Logic 0 = No parity.
• Logic 1 = A parity bit is generated during the transmission while the receiver checks for parity error of the
data character received.
LCR[4]: TX and RX Parity Select
If the parity bit is enabled with LCR bit-3 set to a logic 1, LCR bit-4 selects the even or odd parity format.
• Logic 0 = ODD Parity is generated by forcing an odd number of logic 1’s in the transmitted character. The
receiver must be programmed to check the same format (default).
• Logic 1 = EVEN Parity is generated by forcing an even number of logic 1’s in the transmitted character. The
receiver must be programmed to check the same format.
LCR[5]: TX and RX Parity Select
If the parity bit is enabled, LCR BIT-5 selects the forced parity format.
• LCR BIT-5 = logic 0, parity is not forced (default).
• LCR BIT-5 = logic 1 and LCR BIT-4 = logic 0, parity bit is forced to a logical 1 for the transmit and receive
data.
• LCR BIT-5 = logic 1 and LCR BIT-4 = logic 1, parity bit is forced to a logical 0 for the transmit and receive
data.
TABLE 11: PARITY SELECTION
LCR BIT-5 LCR BIT-4 LCR BIT-3
PARITY SELECTION
X
X
0
No parity
0
0
1
Odd parity
0
1
1
Even parity
1
0
1
Force parity to mark, “1”
1
1
1
Forced parity to space, “0”
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LCR[6]: Transmit Break Enable
When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a
“space", LOW state). This condition remains, until disabled by setting LCR bit-6 to a logic 0.
• Logic 0 = No TX break condition (default).
• Logic 1 = Forces the transmitter output (TX) to a “space”, LOW, for alerting the remote receiver of a line
break condition.
LCR[7]: Baud Rate Divisors Enable
Baud rate generator divisor (DLL, DLM and DLD) enable.
• Logic 0 = Data registers are selected (default).
• Logic 1 = Divisor latch registers are selected.
4.7
Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write
The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs.
MCR[0]: DTR# Output
The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a
general purpose output.
• Logic 0 = Force DTR# output HIGH (default).
• Logic 1 = Force DTR# output LOW.
MCR[1]: RTS# Output
The RTS# pin is a modem control output and may be used for automatic hardware flow control by enabled by
EFR bit-6. The RTS# pin can also be used for Auto RS485 Half-Duplex direction control enabled by FCTR bit3. If the modem interface is not used, this output may be used as a general purpose output.
• Logic 0 = Force RTS# HIGH (default).
• Logic 1 = Force RTS# LOW.
MCR[2]: Reserved
OP1# is not available as an output pin on the M2750. But it is available for use during Internal Loopback Mode.
In the Loopback Mode, this bit is used to write the state of the modem RI# interface signal.
MCR[3]: OP2# Output / INT Output Enable
This bit enables or disables the operation of INT, interrupt output. If INT output is not used, OP2# can be used
as a general purpose output.
• Logic 0 = INT (A-B) outputs disabled (three state mode) and OP2# output set HIGH(default).
• Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output set LOW.
MCR[4]: Internal Loopback Enable
• Logic 0 = Disable loopback mode (default).
• Logic 1 = Enable local loopback mode, see loopback section and Figure 12.
MCR[5]: Xon-Any Enable (requires EFR bit-4=1)
• Logic 0 = Disable Xon-Any function (default).
• Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation.
The RX character will be loaded into the RX FIFO, unless the RX character is an Xon or Xoff character and
the M2750 is programmed to use the Xon/Xoff flow control.
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MCR[6]: Infrared Encoder/Decoder Enable (requires EFR bit-4=1)
• Logic 0 = Enable the standard modem receive and transmit input/output interface (default).
• Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. The TX/RX output/input are routed to the
infrared encoder/decoder. The data input and output levels conform to the IrDA infrared interface
requirement. While in this mode, the infrared TX output will be idling LOW. SEE”INFRARED MODE” ON
PAGE 19.
MCR[7]: Clock Prescaler Select (requires EFR bit-4=1)
• Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable
Baud Rate Generator without further modification, i.e., divide by one (default).
• Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and
feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth.
4.8
Line Status Register (LSR) - Read Only
This register provides the status of data transfers between the UART and the host.
LSR[0]: Receive Data Ready Indicator
• Logic 0 = No data in receive holding register or FIFO (default).
• Logic 1 = Data has been received and is saved in the receive holding register or FIFO.
LSR[1]: Receiver Overrun Error Flag
• Logic 0 = No overrun error (default).
• Logic 1 = Overrun error. A data overrun error condition occurred in the receive shift register. This happens
when additional data arrives while the FIFO is full. In this case the previous data in the receive shift register
is overwritten. Note that under this condition the data byte in the receive shift register is not transferred into
the FIFO, therefore the data in the FIFO is not corrupted by the error.
LSR[2]: Receive Data Parity Error Tag
• Logic 0 = No parity error (default).
• Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect.
This error is associated with the character available for reading in RHR.
LSR[3]: Receive Data Framing Error Tag
• Logic 0 = No framing error (default).
• Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with
the character available for reading in RHR.
LSR[4]: Receive Break Error Tag
• Logic 0 = No break condition (default).
• Logic 1 = The receiver received a break signal (RX was LOW for at least one character frame time). In the
FIFO mode, only one break character is loaded into the FIFO.
LSR[5]: Transmit Holding Register Empty Flag
This bit is the Transmit Holding Register Empty indicator. The THR bit is set to a logic 1 when the last data byte
is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0
concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set
when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte.
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LSR[6]: THR and TSR Empty Flag
This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or
TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and
transmit shift register are both empty.
LSR[7]: Receive FIFO Data Error Flag
• Logic 0 = No FIFO error (default).
• Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error
or break indication is in the FIFO data. This bit clears when there is no more error(s) in any of the bytes in the
RX FIFO.
4.9
Modem Status Register (MSR) - Read Only
This register provides the current state of the modem interface input signals. Lower four bits of this register are
used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem
changes state. These bits may be used for general purpose inputs when they are not used with modem
signals.
MSR[0]: Delta CTS# Input Flag
• Logic 0 = No change on CTS# input (default).
• Logic 1 = The CTS# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3).
MSR[1]: Delta DSR# Input Flag
• Logic 0 = No change on DSR# input (default).
• Logic 1 = The DSR# input has changed state since the last time it was monitored. A modem status interrupt
will be generated if MSR interrupt is enabled (IER bit-3).
MSR[2]: Delta RI# Input Flag
• Logic 0 = No change on RI# input (default).
• Logic 1 = The RI# input has changed from a LOW to HIGH, ending of the ringing signal. A modem status
interrupt will be generated if MSR interrupt is enabled (IER bit-3).
MSR[3]: Delta CD# Input Flag
• Logic 0 = No change on CD# input (default).
• Logic 1 = Indicates that the CD# input has changed state since the last time it was monitored. A modem
status interrupt will be generated if MSR interrupt is enabled (IER bit-3).
MSR[4]: CTS Input Status
CTS# pin may function as automatic hardware flow control signal input if it is enabled and selected by Auto
CTS (EFR bit-7). Auto CTS flow control allows starting and stopping of local data transmissions based on the
modem CTS# signal. A HIGH on the CTS# pin will stop UART transmitter as soon as the current character has
finished transmission, and a LOW will resume data transmission. Normally MSR bit-4 bit is the complement of
the CTS# input. However in the loopback mode, this bit is equivalent to the RTS# bit in the MCR register. The
CTS# input may be used as a general purpose input when the modem interface is not used.
MSR[5]: DSR Input Status
Normally this bit is the complement of the DSR# input. In the loopback mode, this bit is equivalent to the DTR#
bit in the MCR register. The DSR# input may be used as a general purpose input when the modem interface is
not used.
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MSR[6]: RI Input Status
Normally this bit is the complement of the RI# input. In the loopback mode this bit is equivalent to bit-2 in the
MCR register. The RI# input may be used as a general purpose input when the modem interface is not used.
MSR[7]: CD Input Status
Normally this bit is the complement of the CD# input. In the loopback mode this bit is equivalent to bit-3 in the
MCR register. The CD# input may be used as a general purpose input when the modem interface is not used.
4.10
Scratch Pad Register (SPR) - Read/Write
This is a 8-bit general purpose register for the user to store temporary data. The content of this register is
preserved during sleep mode but becomes 0xFF (default) after a reset or a power off-on cycle.
4.11
Enhanced Mode Select Register (EMSR)
This register replaces SPR (during a Write) and is accessible only when FCTR[6] = 1.
EMSR[1:0]: Receive/Transmit FIFO Level Count (Write-Only)
When Scratchpad Swap (FCTR[6]) is asserted, EMSR bits 1-0 controls what mode the FIFO Level Counter is
operating in.
TABLE 12: SCRATCHPAD SWAP SELECTION
FCTR[6] EMSR[1]
EMSR[0] Scratchpad is
0
X
X
Scratchpad
1
X
0
RX FIFO Level Counter Mode
1
0
1
TX FIFO Level Counter Mode
1
1
1
Alternate RX/TX FIFO Counter Mode
During Alternate RX/TX FIFO Level Counter Mode, the first value read after EMSR bits 1-0 have been
asserted will always be the RX FIFO Level Counter. The second value read will correspond with the TX FIFO
Level Counter. The next value will be the RX FIFO Level Counter again, then the TX FIFO Level Counter and
so on and so forth.
EMSR[2]: Reserved
EMSR[3]: Automatic RS485 Half-Duplex Control Output Inversion
• Logic 0 = RTS# output is LOW during TX and HIGH during RX (default, compatible with 16C2850).
• Logic 1 = RTS# output is HIGH during TX and LOW during RX.
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EMSR[5:4]: Extended RTS Hysteresis
TABLE 13: AUTO RTS HYSTERESIS
EMSR
BIT-5
EMSR
BIT-4
FCTR
BIT-1
FCTR
BIT-0
RTS#
HYSTERESIS
(CHARACTERS)
0
0
0
0
0
0
0
0
0
0
1
1
0
1
0
1
0
±4
±6
±8
0
0
0
0
1
1
1
1
0
0
1
1
0
1
0
1
±8
±16
±24
±32
1
1
1
1
0
0
0
0
0
0
1
1
0
1
0
1
±40
±44
±48
±52
1
1
1
1
1
1
1
1
0
0
1
1
0
1
0
1
±12
±20
±28
±36
EMSR[6]: LSR Interrupt Mode
• Logic 0 = LSR Interrupt Delayed (for 16C2550 compatibility, default). LSR bits 2, 3, and 4 will generate an
interrupt when the character with the error is in the RHR.
• Logic 1 = LSR Interrupt Immediate. LSR bits 2, 3, and 4 will generate an interrupt as soon as the character is
received into the FIFO.
EMSR[7]: 16X Sampling Rate Mode
Logic 0 = 8X Sampling Rate.
Logic 1 = 16X Sampling Rate (default).
4.12
FIFO Level Register (FLVL) - Read-Only
The FIFO Level Register replaces the Scratchpad Register (during a Read) when FCTR[6] = 1. Note that this is
not identical to the FIFO Data Count Register which can be accessed when LCR = 0xBF.
FLVL[7:0]: FIFO Level Register
This register provides the FIFO counter level for the RX FIFO or the TX FIFO or both depending on EMSR[1:0].
See Table 12 for details.
4.13
Baud Rate Generator Registers (DLL, DLM and DLD) - Read/Write
These registers make-up the value of the baud rate divisor. The concatenation of the contents of DLM and
DLL is a 16-bit value is then added to DLD/16 to achieve the fractional baud rate divisor. DLD must be enabled
via EFR bit-4 before it can be accessed. SEE”PROGRAMMABLE BAUD RATE GENERATOR WITH
FRACTIONAL DIVISOR” ON PAGE 11.
4.14
Device Identification Register (DVID) - Read Only
This register contains the device ID (0x0A for XR16M2750). Prior to reading this register, DLL and DLM should
be set to 0x00 (DLD = 0xXX).
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4.15
REV. P1.0.0
Device Revision Register (DREV) - Read Only
This register contains the device revision information. For example, 0x01 means revision A. Prior to reading
this register, DLL and DLM should be set to 0x00 (DLD = 0xXX).
4.16
Trigger Level Register (TRG) - Write-Only
User Programmable Transmit/Receive Trigger Level Register. If both the programmable TX and RX trigger
levels are used, the TX trigger levels must be set before the RX trigger levels.
TRG[7:0]: Trigger Level Register
These bits are used to program desired trigger levels when trigger Table-D is selected. FCTR bit-7 selects
between programming the RX Trigger Level (a logic 0) and the TX Trigger Level (a logic 1).
4.17
RX/TX FIFO Level Count Register (FC) - Read-Only
This register is accessible when LCR = 0xBF. Note that this register is not identical to the FIFO Level Count
Register which is located in the general register set when FCTR bit-6 = 1 (Scratchpad Register Swap). It is
suggested to read the FIFO Level Count Register at the Scratchpad Register location when FCTR bit-6 = 1.
See Table 12.
FC[7:0]: RX/TX FIFO Level Count
Receive/Transmit FIFO Level Count. Number of characters in Receiver FIFO (FCTR[7] = 0) or Transmitter
FIFO (FCTR[7] = 1) can be read via this register. Reading this register is not recommended when transmitting
or receiving data.
4.18
Feature Control Register (FCTR) - Read/Write
This register controls the XR16M2750 functions that are not available in ST16C2450 or ST16C2550.
FCTR[1:0]: RTS Hysteresis
User selectable RTS# hysteresis levels for hardware flow control application. After reset, these bits are set to
“0” to select the next trigger level for hardware flow control. See Table 13 for more details.
FCTR[2]: IrDa RX Inversion
• Logic 0 = Select RX input as encoded IrDa data (Idle state will be LOW).
• Logic 1 = Select RX input as inverted encoded IrDa data (Idle state will be HIGH).
FCTR[3]: Auto RS-485 Direction Control
• Logic 0 = Standard ST16C550 mode. Transmitter generates an interrupt when transmit holding register
becomes empty and transmit shift register is shifting data out.
• Logic 1 = Enable Auto RS485 Direction Control function. The direction control signal, RTS# pin, changes its
output logic state from LOW to HIGH one bit time after the last stop bit of the last character is shifted out.
Also, the Transmit interrupt generation is delayed until the transmitter shift register becomes empty. The
RTS# output pin will automatically return to a LOW when a data byte is loaded into the TX FIFO. However,
RTS# behavior can be inverted by setting EMSR[3] = 1.
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FCTR[5:4]: Transmit/Receive Trigger Table Select
See Table 10 for more details.
TABLE 14: TRIGGER TABLE SELECT
FCTR
BIT-5
FCTR
BIT-4
0
0
Table-A (TX/RX)
0
1
Table-B (TX/RX)
1
0
Table-C (TX/RX)
1
1
Table-D (TX/RX)
TABLE
FCTR[6]: Scratchpad Swap
• Logic 0 = Scratch Pad register is selected as general read and write register. ST16C550 compatible mode.
• Logic 1 = FIFO Level Count register (Read-Only), Enhanced Mode Select Register (Write-Only). Number of
characters in transmit or receive FIFO can be read via scratch pad register when this bit is set. Enhanced
Mode Select Register is selected when it is written into.
FCTR[7]: Programmable Trigger Register Select
If using both programmable TX and RX trigger levels, TX trigger levels must be set before RX trigger levels.
• Logic 0 = Registers TRG and FC selected for RX.
• Logic 1 = Registers TRG and FC selected for TX.
4.19
Enhanced Feature Register (EFR)
Enhanced features are enabled or disabled using this register. Bit 0-3 provide single or dual consecutive
character software flow control selection (see Table 15). When the Xon1 and Xon2 and Xoff1 and Xoff2 modes
are selected, the double 8-bit words are concatenated into two sequential characters. Caution: note that
whenever changing the TX or RX flow control bits, always reset all bits back to logic 0 (disable) before
programming a new setting.
EFR[3:0]: Software Flow Control Select
Single character and dual sequential characters software flow control is supported. Combinations of software
flow control can be selected by programming these bits.
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TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3
CONT-3
EFR BIT-2
CONT-2
EFR BIT-1
CONT-1
EFR BIT-0
CONT-0
0
0
0
0
No TX and RX flow control (default and reset)
0
0
X
X
No transmit flow control
1
0
X
X
Transmit Xon1, Xoff1
0
1
X
X
Transmit Xon2, Xoff2
1
1
X
X
Transmit Xon1 and Xon2, Xoff1 and Xoff2
X
X
0
0
No receive flow control
X
X
1
0
Receiver compares Xon1, Xoff1
X
X
0
1
Receiver compares Xon2, Xoff2
1
0
1
1
Transmit Xon1, Xoff1
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
0
1
1
1
Transmit Xon2, Xoff2
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1
1
1
1
Transmit Xon1 and Xon2, Xoff1 and Xoff2,
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
0
0
1
1
No transmit flow control,
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL
EFR[4]: Enhanced Function Bits Enable
Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 5-7, and DLD
to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the new values.
This feature prevents legacy software from altering or overwriting the enhanced functions once set. Normally, it
is recommended to leave it enabled, logic 1.
• Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 57, and DLD are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits 4-5,
MCR bits 5-7, and DLD are set to a logic 0 to be compatible with ST16C550 mode (default).
• Logic 1 = Enables the above-mentioned register bits to be modified by the user.
EFR[5]: Special Character Detect Enable
• Logic 0 = Special Character Detect Disabled (default).
• Logic 1 = Special Character Detect Enabled. The UART compares each incoming receive character with
data in Xoff-2 register. If a match exists, the receive data will be transferred to FIFO and ISR bit-4 will be set
to indicate detection of the special character. Bit-0 corresponds with the LSB bit of the receive character. If
flow control is set for comparing Xon1, Xoff1 (EFR [1:0]= ‘10’) then flow control and special character work
normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]= ‘01’) then flow control works
normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character
interrupt, if enabled via IER bit-5.
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EFR[6]: Auto RTS Flow Control Enable
RTS# output may be used for hardware flow control by setting EFR bit-6 to logic 1. When Auto RTS is
selected, an interrupt will be generated when the receive FIFO is filled to the programmed trigger level and
RTS de-asserts HIGH at the next upper trigger level or hysteresis level. RTS# will return LOW when FIFO data
falls below the next lower trigger level. The RTS# output must be asserted (LOW) before the auto RTS can
take effect. RTS# pin will function as a general purpose output when hardware flow control is disabled.
• Logic 0 = Automatic RTS flow control is disabled (default).
• Logic 1 = Enable Automatic RTS flow control.
EFR[7]: Auto CTS Flow Control Enable
Automatic CTS Flow Control.
• Logic 0 = Automatic CTS flow control is disabled (default).
• Logic 1 = Enable Automatic CTS flow control. Data transmission stops when CTS# input de-asserts HIGH.
Data transmission resumes when CTS# returns LOW.
4.19.1
Software Flow Control Registers (XOFF1, XOFF2, XON1, XON2) - Read/Write
These registers are used as the programmable software flow control characters xoff1, xoff2, xon1, and xon2.
For more details, see Table 6.
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TABLE 16: UART RESET CONDITIONS FOR CHANNEL A AND B
REGISTERS
RESET STATE
DLM, DLL
DLM = 0x00 and DLL = 0x01. Only resets to these values during a power up.
They do not reset when the Reset Pin is asserted.
DLD
Bits 7-0 = 0x00
RHR
Bits 7-0 = 0xXX
THR
Bits 7-0 = 0xXX
IER
Bits 7-0 = 0x00
FCR
Bits 7-0 = 0x00
ISR
Bits 7-0 = 0x01
LCR
Bits 7-0 = 0x00
MCR
Bits 7-0 = 0x00
LSR
Bits 7-0 = 0x60
MSR
Bits 3-0 = Logic 0
Bits 7-4 = Logic levels of the inputs inverted
SPR
Bits 7-0 = 0xFF
EMSR
Bits 7-0 = 0x80
FLVL
Bits 7-0 = 0x00
EFR
Bits 7-0 = 0x00
XON1
Bits 7-0 = 0x00
XON2
Bits 7-0 = 0x00
XOFF1
Bits 7-0 = 0x00
XOFF2
Bits 7-0 = 0x00
FC
Bits 7-0 = 0x00
I/O SIGNALS
RESET STATE
TX
HIGH
OP2#
HIGH
RTS#
HIGH
DTR#
HIGH
RXRDY#
HIGH
TXRDY#
LOW
INT
Three-State Condition
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ABSOLUTE MAXIMUM RATINGS
Power Supply Range
4 Volts
Voltage at Any Pin
GND-0.3V to VCC+0.3V
Operating Temperature
-40o to +85oC
Storage Temperature
-65o to +150oC
Package Dissipation
500 mW
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: ± 15%)
Thermal Resistance (48-TQFP)
theta-ja =59oC/W, theta-jc = 16oC/W
Thermal Resistance (32-QFN)
theta-ja = 33oC/W, theta-jc = 22oC/W
ELECTRICAL CHARACTERISTICS
DC ELECTRICAL CHARACTERISTICS
TA=-40O TO +85OC, VCC IS 1.62V TO 3.6V
LIMITS
1.8V
MIN
MAX
LIMITS
2.5V
MIN
MAX
LIMITS
3.3V
MIN
MAX
Clock Input Low Level
-0.3
0.3
-0.3
0.4
-0.3
0.6
V
Clock Input High Level
1.4
VCC
2.0
VCC
2.4
VCC
V
VIL
Input Low Voltage
-0.3
0.2
-0.3
0.5
-0.3
0.7
V
VIH
Input High Voltage
1.4
VCC
1.8
VCC
2.0
VCC
V
VOL
Output Low Voltage
0.4
V
V
V
IOL = 6 mA
V
V
V
IOH = -4 mA
SYMBOL
PARAMETER
VILCK
VIHCK
0.4
0.4
VOH
Output High Voltage
2.4
1.8
1.4
UNITS
CONDITIONS
IOL = 4 mA
IOL = 2 mA
IOH = -2 mA
IOH = -1 mA
IIL
Input Low Leakage
Current
±10
±10
±10
uA
IIH
Input High Leakage
Current
±10
±10
±10
uA
CIN
Input Pin Capacitance
5
5
5
pF
ICC
Power Supply Current
0.5
1.5
2.5
mA
Ext Clk = 2MHz
5
15
30
uA
See Test 1
ISLEEP
Sleep Current
Test 1: The following inputs must remain steady at VCC or GND state to minimize Sleep current: A0-A2, D0D7, IOR#, IOW#, CSA#, CSB# and all modem inputs. Also, RXA and RXB inputs must idle HIGH while asleep.
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Floating inputs will result in sleep currents in the mA range. For PowerSave feature that isolates address, data
and control signals, please see the XR16M2751 datasheet.
AC ELECTRICAL CHARACTERISTICS
UNLESS OTHERWISE NOTED: TA=-40O TO +85OC, VCC=1.62 - 3.63V, 70 PF LOAD WHERE APPLICABLE
SYMBOL
PARAMETER
LIMITS
1.8V ± 10%
MIN
MAX
LIMITS
2.5V ± 10%
MIN
MAX
LIMITS
3.3V ± 10%
MIN
MAX
UNIT
XTAL1
UART Crystal Oscillator
24
32
24
MHz
ECLK
External Clock
32
50
64
MHz
TECLK
External Clock Time Period
15
10
7
ns
TAS
Address Setup Time
0
0
0
ns
TAH
Address Hold Time
0
0
0
ns
TCS
Chip Select Width
65
50
40
ns
TRD
IOR# Strobe Width
65
50
40
ns
TDY
Read Cycle Delay
65
50
40
ns
TRDV
Data Access Time
60
45
35
ns
TDD
Data Disable Time
25
25
25
ns
TWR
IOW# Strobe Width
65
50
40
ns
TDY
Write Cycle Delay
65
50
40
ns
TDS
Data Setup Time
20
10
10
ns
TDH
Data Hold Time
5
5
5
ns
TWDO
Delay From IOW# To Output
0
50
50
ns
TMOD
Delay To Set Interrupt From
MODEM Input
0
50
50
ns
TRSI
Delay To Reset Interrupt From
IOR#
0
50
50
ns
TSSI
Delay From Stop To Set Interrupt
60
1
1
Bclk
TRRI
Delay From IOR# To Reset
Interrupt
25
45
45
ns
TSI
Delay From Stop To Interrupt
45
45
45
ns
TINT
Delay From Initial INT Reset To
Transmit Start
24
Bclk
TWRI
Delay From IOW# To Reset
Interrupt
45
45
45
ns
TSSR
Delay From Stop To Set
RXRDY#
1
1
1
Bclk
TRR
Delay From IOR# To Reset
RXRDY#
45
45
45
ns
8
24
42
8
24
8
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
AC ELECTRICAL CHARACTERISTICS
UNLESS OTHERWISE NOTED: TA=-40O TO +85OC, VCC=1.62 - 3.63V, 70 PF LOAD WHERE APPLICABLE
SYMBOL
PARAMETER
LIMITS
1.8V ± 10%
MIN
MAX
LIMITS
2.5V ± 10%
MIN
MAX
LIMITS
3.3V ± 10%
MIN
MAX
UNIT
TWT
Delay From IOW# To Set
TXRDY#
45
45
45
ns
TSRT
Delay From Center of Start To
Reset TXRDY#
8
8
8
Bclk
TRST
Reset Pulse Width
Bclk
Baud Clock
40
40
40
16X or 8X of data rate
FIGURE 13. CLOCK TIMING
TECLK
TECL
TECH
VIH
External
Clock
VIL
43
ns
Hz
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 14. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B
IOW #
Active
T W DO
RTS#
DTR#
Change of state
Change of state
CD#
CTS#
DSR#
Change of state
Change of state
T MO D
T M OD
INT
Active
Active
Active
T RSI
IOR#
Active
Active
Active
T M OD
Change of state
RI#
FIGURE 15. DATA BUS READ TIMING
A0-A2
Valid Address
TAS
TCS
Valid Address
TAS
TAH
TAH
TCS
CSA#/
CSB#
TDY
TRD
TRD
IOR#
TDD
TRDV
D0-D7
Valid Data
TDD
TRDV
Valid Data
RDTm
44
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 16. DATA BUS WRITE TIMING
A0-A2
Valid Address
Valid Address
TAS
TAS
TAH
TCS
TAH
TCS
CSA#/
CSB#
TDY
TWR
TWR
IOW#
TDH
TDS
TDS
Valid Data
D0-D7
TDH
Valid Data
16Write
FIGURE 17. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
RX
INT
RXRDY#
Start
Bit
D0:D7
Stop
Bit
D0:D7
D0:D7
TSSR
TSSR
TSSR
1 Byte
in RHR
1 Byte
in RHR
1 Byte
in RHR
TSSR
TSSR
Active
Data
Ready
Active
Data
Ready
TRR
TRR
TSSR
Active
Data
Ready
TRR
IOR#
(Reading data
out of RHR)
RXNFM
45
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 18. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B
TX
Start
Bit
IER[1]
enabled
Stop
Bit
D0:D7
D0:D7
ISR is read
D0:D7
ISR is read
ISR is read
INT*
TWRI
TWRI
TWRI
TSRT
TSRT
TSRT
TXRDY#
TWT
TWT
TWT
IOW#
(Loading data
into THR)
*INT is cleared when the ISR is read or when data is loaded into the THR.
TXNonFIFO
FIGURE 19. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B
Start
Bit
RX
S D0:D7
S D0:D7 T
Stop
Bit
D0:D7
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
RX FIFO drops
below RX
Trigger Level
TSSI
INT
FIFO
Empties
TSSR
RX FIFO fills up to RX
Trigger Level or RX Data
Timeout
RXRDY#
First Byte is
Received in
RX FIFO
TRRI
TRR
IOR#
(Reading data out
of RX FIFO)
RXINTDMA#
46
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 20. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B
Start
Bit
RX
Stop
Bit
S D0:D7
S D0:D7 T
D0:D7
S D0:D7 T
S D0:D7 T S D0:D7 T
S D0:D7 T
RX FIFO drops
below RX
Trigger Level
TSSI
INT
RX FIFO fills up to RX
Trigger Level or RX Data
Timeout
FIFO
Empties
TSSR
RXRDY#
TRRI
TRR
IOR#
(Reading data out
of RX FIFO)
RXFIFODMA
FIGURE 21. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B
TX FIFO
Empty
TX
Start
Bit
Stop
Bit
S D0:D7 T
(Unloading)
IER[1]
enabled
Last Data Byte
Transmitted
T S D0:D7 T S D0:D7 T
S D0:D7 T S D0:D7 T
TSI
ISR is read
S D0:D7 T
ISR is read
TSRT
INT*
TX FIFO fills up
to trigger level
TXRDY#
Data in
TX FIFO
TX FIFO
Empty
TWRI
TX FIFO drops
below trigger level
TWT
IOW#
(Loading data
into FIFO)
*INT is cleared when the ISR is read or when TX FIFO fills up to the trigger level.
47
TXDMA#
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
FIGURE 22. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B
Start
Bit
TX
Stop
Bit
Last Data Byte
Transmitted
S D0:D7 T S D0:D7 T
(Unloading)
IER[1]
enabled
D0:D7
S D0:D7 T
ISR Read
S D0:D7 T S D0:D7 T
S D0:D7 T
TSI
TSRT
ISR Read
INT*
TX FIFO fills up
to trigger level
TXRDY#
TX FIFO drops
below trigger level
TWRI
At least 1
empty location
in FIFO
TX FIFO
Full
TWT
IOW#
(Loading data
into FIFO)
*INT cleared when the ISR is read or when TX FIFO fills up to trigger level.
48
TXDMA
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm)
D
D1
36
25
37
24
D1
48
13
1
2
1
B
e
A2
C
A
α
Seating
Plane
A1
L
Note: The control dimension is the millimeter column
INCHES
MILLIMETERS
SYMBOL
MIN
MAX
MIN
MAX
A
0.039
0.047
1.00
1.20
A1
0.002
0.006
0.05
0.15
A2
0.037
0.041
0.95
1.05
B
0.007
0.011
0.17
0.27
C
0.004
0.008
0.09
0.20
D
0.346
0.362
8.80
9.20
D1
0.272
0.280
6.90
7.10
e
0.020 BSC
0.50 BSC
L
0.018
0.030
0.45
0.75
a
0°
7°
0°
7°
49
D
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm)
Note: the actual center pad
is metallic and the size (D2)
is device-dependent with a
typical tolerance of 0.3mm
Note: The control dimension is in millimeter.
INCHES
MILLIMETERS
SYMBOL
MIN
MAX
MIN
MAX
A
0.031
0.039
0.80
1.00
A1
0.000
0.002
0.00
0.05
A3
0.006
0.010
0.15
0.25
D
0.193
0.201
4.90
5.10
D2
0.138
0.150
3.50
3.80
b
0.007
0.012
0.18
0.30
e
0.0197 BSC
0.50 BSC
L
0.012
0.020
0.35
0.45
k
0.008
-
0.20
-
50
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
REVISION HISTORY
DATE
REVISION
June 2007
P1.0.0
DESCRIPTION
Preliminary Datasheet.
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to
improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any
circuits described herein, conveys no license under any patent or other right, and makes no representation that
the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration
purposes and may vary depending upon a user’s specific application. While the information in this publication
has been carefully checked; no responsibility, however, is assumed for inaccuracies.
EXAR Corporation does not recommend the use of any of its products in life support applications where the
failure or malfunction of the product can reasonably be expected to cause failure of the life support system or
to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless
EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has
been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately
protected under the circumstances.
Copyright 2007 EXAR Corporation
Datasheet June 2007.
Send your UART technical inquiry with technical details to hotline: [email protected]
Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited.
51
XR16M2750
PRELIMINARY
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
TABLE OF CONTENTS
GENERAL DESCRIPTION ................................................................................................ 1
APPLICATIONS ............................................................................................................................................... 1
FEATURES .................................................................................................................................................... 1
FIGURE 1. XR16M2750 BLOCK DIAGRAM ........................................................................................................................................ 1
FIGURE 2. PIN OUT ASSIGNMENT ..................................................................................................................................................... 2
ORDERING INFORMATION................................................................................................................................ 2
PIN DESCRIPTIONS ........................................................................................................ 3
1.0 PRODUCT DESCRIPTION....................................................................................................................... 7
2.0 FUNCTIONAL DESCRIPTIONS............................................................................................................... 8
2.1 CPU INTERFACE................................................................................................................................................. 8
FIGURE 3. XR16M2750 DATA BUS INTERCONNECTIONS ................................................................................................................... 8
2.2 DEVICE RESET ................................................................................................................................................... 8
2.3 DEVICE IDENTIFICATION AND REVISION........................................................................................................ 8
2.4 CHANNEL A AND B SELECTION....................................................................................................................... 8
TABLE 1: CHANNEL A AND B SELECT ............................................................................................................................................... 9
2.5 CHANNEL A AND B INTERNAL REGISTERS ................................................................................................... 9
2.6 DMA MODE.......................................................................................................................................................... 9
TABLE 2: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE ............................................................................................. 9
2.7 INTA AND INTB OUTPUTS ............................................................................................................................... 10
TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER ...................................................................................................... 10
TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER ............................................................................................................. 10
2.8 CRYSTAL OSCILLATOR OR EXTERNAL CLOCK INPUT .............................................................................. 10
FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS ............................................................................................................................... 10
2.9 PROGRAMMABLE BAUD RATE GENERATOR WITH FRACTIONAL DIVISOR............................................ 11
FIGURE 5. BAUD RATE GENERATOR ............................................................................................................................................... 12
TABLE 5: TYPICAL DATA RATES WITH A 24 MHZ CRYSTAL OR EXTERNAL CLOCK AT 16X SAMPLING ................................................... 12
2.10 TRANSMITTER ................................................................................................................................................ 13
2.10.1 TRANSMIT HOLDING REGISTER (THR) - WRITE ONLY .........................................................................................
2.10.2 TRANSMITTER OPERATION IN NON-FIFO MODE ..................................................................................................
FIGURE 6. TRANSMITTER OPERATION IN NON-FIFO MODE ..............................................................................................................
2.10.3 TRANSMITTER OPERATION IN FIFO MODE ...........................................................................................................
FIGURE 7. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE .....................................................................................
13
13
13
13
14
2.11 RECEIVER ....................................................................................................................................................... 14
2.11.1 RECEIVE HOLDING REGISTER (RHR) - READ-ONLY ............................................................................................ 14
FIGURE 8. RECEIVER OPERATION IN NON-FIFO MODE .................................................................................................................... 15
FIGURE 9. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE ......................................................................... 15
2.12 AUTO RTS (HARDWARE) FLOW CONTROL ................................................................................................ 16
2.13 AUTO RTS HYSTERESIS............................................................................................................................... 16
2.14 AUTO CTS FLOW CONTROL ........................................................................................................................ 16
FIGURE 10. AUTO RTS AND CTS FLOW CONTROL OPERATION ....................................................................................................... 17
2.15 AUTO XON/XOFF (SOFTWARE) FLOW CONTROL...................................................................................... 18
TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL ............................................................................................................... 18
2.16 SPECIAL CHARACTER DETECT .................................................................................................................. 18
2.17 AUTO RS485 HALF-DUPLEX CONTROL ..................................................................................................... 18
2.18 INFRARED MODE ........................................................................................................................................... 19
FIGURE 11. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING .......................................................................... 19
2.19 SLEEP MODE WITH AUTO WAKE-UP.......................................................................................................... 20
2.20 INTERNAL LOOPBACK ................................................................................................................................. 21
FIGURE 12. INTERNAL LOOP BACK IN CHANNEL A AND B ................................................................................................................ 21
3.0 UART INTERNAL REGISTERS ............................................................................................................. 22
TABLE 7: UART CHANNEL A AND B UART INTERNAL REGISTERS ....................................................................................... 22
TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1 ......................................... 23
4.0 INTERNAL REGISTER DESCRIPTIONS............................................................................................... 24
4.1 RECEIVE HOLDING REGISTER (RHR) - READ- ONLY .................................................................................. 24
4.2 TRANSMIT HOLDING REGISTER (THR) - WRITE-ONLY ............................................................................... 24
4.3 INTERRUPT ENABLE REGISTER (IER) - READ/WRITE................................................................................. 24
4.3.1 IER VERSUS RECEIVE FIFO INTERRUPT MODE OPERATION ............................................................................... 25
4.3.2 IER VERSUS RECEIVE/TRANSMIT FIFO POLLED MODE OPERATION .................................................................. 25
4.4 INTERRUPT STATUS REGISTER (ISR) - READ-ONLY .................................................................................. 26
I
PRELIMINARY
XR16M2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. P1.0.0
4.4.1 INTERRUPT GENERATION: ........................................................................................................................................ 26
4.4.2 INTERRUPT CLEARING: ............................................................................................................................................. 26
TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL ....................................................................................................................... 27
4.5 FIFO CONTROL REGISTER (FCR) - WRITE-ONLY ........................................................................................ 27
TABLE 10: TRANSMIT AND RECEIVE FIFO TRIGGER TABLE AND LEVEL SELECTION .......................................................................... 29
4.6 LINE CONTROL REGISTER (LCR) - READ/WRITE ........................................................................................ 29
TABLE 11: PARITY SELECTION ........................................................................................................................................................ 30
4.7 MODEM CONTROL REGISTER (MCR) OR GENERAL PURPOSE OUTPUTS CONTROL - READ/WRITE .
4.8 LINE STATUS REGISTER (LSR) - READ ONLY..............................................................................................
4.9 MODEM STATUS REGISTER (MSR) - READ ONLY .......................................................................................
4.10 SCRATCH PAD REGISTER (SPR) - READ/WRITE .......................................................................................
4.11 ENHANCED MODE SELECT REGISTER (EMSR) .........................................................................................
31
32
33
34
34
TABLE 12: SCRATCHPAD SWAP SELECTION .................................................................................................................................... 34
TABLE 13: AUTO RTS HYSTERESIS ................................................................................................................................................ 35
4.12 FIFO LEVEL REGISTER (FLVL) - READ-ONLY ............................................................................................
4.13 BAUD RATE GENERATOR REGISTERS (DLL, DLM AND DLD) - READ/WRITE .......................................
4.14 DEVICE IDENTIFICATION REGISTER (DVID) - READ ONLY.......................................................................
4.15 DEVICE REVISION REGISTER (DREV) - READ ONLY.................................................................................
4.16 TRIGGER LEVEL REGISTER (TRG) - WRITE-ONLY ....................................................................................
4.17 RX/TX FIFO LEVEL COUNT REGISTER (FC) - READ-ONLY .......................................................................
4.18 FEATURE CONTROL REGISTER (FCTR) - READ/WRITE ..........................................................................
35
35
35
36
36
36
36
TABLE 14: TRIGGER TABLE SELECT ............................................................................................................................................... 37
4.19 ENHANCED FEATURE REGISTER (EFR) ..................................................................................................... 37
TABLE 15: SOFTWARE FLOW CONTROL FUNCTIONS ........................................................................................................................ 38
4.19.1 SOFTWARE FLOW CONTROL REGISTERS (XOFF1, XOFF2, XON1, XON2) - READ/WRITE .............................. 39
TABLE 16: UART RESET CONDITIONS FOR CHANNEL A AND B ............................................................................................ 40
ABSOLUTE MAXIMUM RATINGS ................................................................................. 41
TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: ± 15%) 41
ELECTRICAL CHARACTERISTICS............................................................................... 41
DC ELECTRICAL CHARACTERISTICS............................................................................................................. 41
TA=-40o to +85oC, Vcc is 1.62V to 3.6V ............................................................................................................... 41
AC ELECTRICAL CHARACTERISTICS ............................................................................................................. 42
Unless otherwise noted: TA=-40o to +85oC, Vcc=1.62 - 3.63V, 70 pF load where applicable................................ 42
FIGURE 13. CLOCK TIMING............................................................................................................................................................. 43
FIGURE 14. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B ................................................................................................. 44
FIGURE 15. DATA BUS READ TIMING .............................................................................................................................................. 44
FIGURE 16. DATA BUS WRITE TIMING ............................................................................................................................................ 45
FIGURE 17. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ......................................................... 45
FIGURE 18. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B ....................................................... 46
FIGURE 19. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B........................................ 46
FIGURE 20. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B......................................... 47
FIGURE 21. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B ........................... 47
FIGURE 22. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B ............................ 48
PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm) .................................................................................. 49
PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm).............................................. 50
REVISION HISTORY ..................................................................................................................................... 51
TABLE OF CONTENTS ..................................................................................................... I
II