NSC NS16C2752TVA

August 2006
NS16C2552/NS16C2752
Dual UART with 16-byte/64-byte FIFO’s and up to
5 Mbit/s Data Rate
1.0 General Description
2.0 Features
The NS16C2552 and NS16C2752 are dual channel Universal Asynchronous Receiver/Transmitter (DUART). The footprint and the functions are compatible to the PC16552D,
while new features are added to the UART device. These
features include low voltage support, 5V tolerant inputs,
enhanced features, enhanced register set, and higher data
rate.
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The two serial channels are completely independent of each
other, except for a common CPU interface and crystal input.
On power-up both channels are functionally identical to the
PC16552D. Each channel can operate with on-chip transmitter and receiver FIFO’s (in FIFO mode).
In the FIFO mode each channel is capable of buffering 16
bytes (for NS16C2552) or 64 bytes (for NS16C2752) of data
in both the transmitter and receiver. The receiver FIFO also
has additional 3 bits of error data per location. All FIFO
control logic is on-chip to minimize system software overhead and maximize system efficiency.
To improve the CPU processing bandwidth, the data transfers between the DUART and the CPU can be done using
DMA controller. Signaling for DMA transfers is done through
two pins per channel (TXRDY and RXRDY). The RXRDY
function is multiplexed on one pin with the OUT2 and BAUDOUT functions. The configuration is through Alternate Function Register.
The fundamental function of the UART is converting between parallel and serial data. Serial-to-parallel conversion
is done on the UART receiver and parallel-to-serial conversion is done on the transmitter. The CPU can read the
complete status of each channel at any time. Status information reported includes the type and condition of the transfer operations being performed by the DUART, as well as
any error conditions (parity, overrun, framing, or break interrupt).
The NS16C2552 and NS16C2752 include one programmable baud rate generator for each channel. Each baud rate
generator is capable of dividing the clock input by divisors of
1 to (216 - 1), and producing a 16X clock for driving the
internal transmitter logic and for receiver sampling circuitry.
The NS16C2552 and NS16C2752 have complete MODEMcontrol capability, and a processor-interrupt system. The
interrupts can be programmed by the user to minimize the
processing required to handle the communications link.
© 2006 National Semiconductor Corporation
DS202048
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Dual independent UART
Up to 5 Mbits/s data transfer rate
2.97 V to 5.50 V operational Vcc
5 V tolerant I/Os in the entire supply voltage range
Industrial Temperature: -40˚C to 85˚C
Default registers are identical to the PC16552D
NS16C2552/NS16C2752 is pin-to-pin compatible to
NSC PC16552D, EXAR ST16C2552, XR16C2552, XR
16L2552, and Phillips SC16C2552B
NS16C2752 is compatible to EXAR XR16L2752, and
register compatible to Phillips SC16C752
Auto Hardware Flow Control (Auto-CTS, Auto-RTS)
Auto Software Flow Control (Xon, Xoff, and Xon-any)
Fully programmable character length (5, 6, 7, or 8) with
even, odd, or no parity, stop bit
Adds or deletes standard asynchronous communication
bits (start, stop, and parity) to or from the serial data
Independently controlled and prioritized transmit and
receive interrupts
Complete line status reporting capabilities
Line break generation and detection
Internal diagnostic capabilities
— Loopback controls for communications link fault
isolation
— Break, parity, overrun, framing error detection
Programmable baud generators divide any input clock
by 1 to (216 - 1) and generate the 16 X clock
IrDA v1.0 wireless Infrared encoder/decoder
DMA operation (TXRDY/RXRDY)
Concurrent write to DUART internal register channels 1
and 2
Multi-function output allows more package functions with
fewer I/O pins
44-PLCC or 48-TQFP package
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NS16C2552/NS16C2752 Dual UART with 16-byte/64-byte FIFO’s and up to 5 Mbit/s Data Rate
PRELIMINARY
NS16C2552/NS16C2752
Table of Contents
1.0 General Description ..................................................................................................................................... 1
2.0 Features ....................................................................................................................................................... 1
3.0 System Block Diagram ................................................................................................................................. 4
4.0 Connection Diagrams ................................................................................................................................... 4
5.0 Pin Descriptions ........................................................................................................................................... 5
5.1 PARALLEL BUS INTERFACE ................................................................................................................... 5
5.2 SERIAL IO INTERFACE ............................................................................................................................ 6
5.3 CLOCK AND RESET ................................................................................................................................ 8
5.4 POWER AND GROUND ........................................................................................................................... 8
6.0 Register Set ................................................................................................................................................. 9
6.1 RECEIVE BUFFER REGISTER (RBR) ................................................................................................... 11
6.2 TRANSMIT HOLDING REGISTER (THR) .............................................................................................. 12
6.3 INTERRUPT ENABLE REGISTER (IER) ................................................................................................ 12
6.4 INTERRUPT IDENTIFICATION REGISTER (IIR) ................................................................................... 13
6.5 FIFO CONTROL REGISTER (FCR) ....................................................................................................... 14
6.6 LINE CONTROL REGISTER (LCR) ........................................................................................................ 16
6.7 MODEM CONTROL REGISTER (MCR) ................................................................................................. 18
6.8 LINE STATUS REGISTER (LSR) ............................................................................................................ 20
6.9 MODEM STATUS REGISTER (MSR) ..................................................................................................... 22
6.10 SCRATCHPAD REGISTER (SCR) ........................................................................................................ 23
6.11 PROGRAMMABLE BAUD GENERATOR ............................................................................................. 23
6.12 ALTERNATE FUNCTION REGISTER (AFR) ........................................................................................ 24
6.13 DEVICE IDENTIFICATION REGISTER (ID) ......................................................................................... 24
6.14 ENHANCED FEATURE REGISTER (EFR) .......................................................................................... 25
6.15 SOFTWARE FLOW CONTROL REGISTERS (SFR) ........................................................................... 26
7.0 Operation and Configuration ...................................................................................................................... 27
7.1 CLOCK INPUT ........................................................................................................................................ 27
7.2 RESET ..................................................................................................................................................... 27
7.3 RECEIVER OPERATION ........................................................................................................................ 27
7.3.1 Receive in FIFO Mode ...................................................................................................................... 28
7.3.2 Receive in non-FIFO Mode ............................................................................................................... 28
7.3.3 Receive Hardware Flow Control ........................................................................................................ 29
7.3.4 Receive Flow Control Interrupt .......................................................................................................... 29
7.4 TRANSMIT OPERATION ........................................................................................................................ 29
7.4.1 Transmit in FIFO Mode ...................................................................................................................... 29
7.4.2 Transmit in non-FIFO Mode .............................................................................................................. 30
7.4.3 Transmit Hardware Flow Control ....................................................................................................... 31
7.4.4 Transmit Flow Control Interrupt ......................................................................................................... 31
7.5 SOFTWARE XON/XOFF FLOW CONTROL .......................................................................................... 31
7.6 SPECIAL CHARACTER DETECT .......................................................................................................... 31
7.7 SLEEP MODE ......................................................................................................................................... 32
7.8 INTERNAL LOOPBACK MODE .............................................................................................................. 32
7.9 DMA OPERATION ................................................................................................................................... 32
7.10 INFRARED MODE ................................................................................................................................ 32
8.0 Design Notes .............................................................................................................................................. 34
8.1 DEBUGGING HINTS ............................................................................................................................... 34
8.2 CLOCK FREQUENCY ACCURACY ....................................................................................................... 34
8.3 CRYSTAL REQUIREMENTS .................................................................................................................. 34
8.4 CONFIGURATION EXAMPLES .............................................................................................................. 35
8.4.1 Set Baud Rate ................................................................................................................................... 35
8.4.2 Configure Prescaler Output ............................................................................................................... 35
8.4.3 Set Xon and Xoff flow control ............................................................................................................ 35
8.4.4 Set Software Flow Control ................................................................................................................. 35
8.4.5 Configure Tx/Rx FIFO Threshold ...................................................................................................... 35
8.4.6 Tx and Rx Hardware Flow Control .................................................................................................... 35
8.4.7 Tx and Rx DMA Control .................................................................................................................... 35
8.5 DIFFERENCES BETWEEN THE PC16552D AND NS16C2552/2752 ................................................... 36
8.6 NOTES ON TX FIFO OF NS16C2752 .................................................................................................... 36
9.0 Absolute Maximum Ratings ....................................................................................................................... 37
10.0 DC and AC Specifications ........................................................................................................................ 37
10.1 DC SPECIFICATIONS ........................................................................................................................... 37
10.2 CAPACITANCE ...................................................................................................................................... 37
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(Continued)
10.3 AC SPECIFICATIONS ........................................................................................................................... 37
11.0 Timing Diagrams ...................................................................................................................................... 39
12.0 Physical Dimensions ................................................................................................................................ 42
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NS16C2552/NS16C2752
Table of Contents
NS16C2552/NS16C2752
3.0 System Block Diagram
20204801
4.0 Connection Diagrams
20204802
44–PLCC
Order Number NS16C2552TVA, NS16C2752TVA;
See NS Package Number V44A
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20204830
48–TQFP
Order Number NS16C2552TVS, NS16C2752TVS;
See NS Package Number VBC48A
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The I/O types are as follows:
The NS16C2552/NS16C2752 pins are classified into the
following interface categories.
• Bus Interface
Type: I
Input
Type: O
Output
Type: IO_Z
TRI-STATE I/O
NS16C2552/NS16C2752
5.0 Pin Descriptions
• Serial I/O Interface
• Clock and Reset
• Power supply and Ground pins
Serial channel number (1 or 2) is designated by a numerical
suffix after each pin name. If a numerical suffix (1 or 2) is not
associated with the pin name, the information applies to both
channels.
5.1 PARALLEL BUS INTERFACE
Signal
Name
D7
D6
D5
D4
D3
D2
D1
D0
Type
IO_Z
PLCC
Pin #
TQFP
Pin #
9
8
7
6
5
4
3
2
3
2
1
48
47
46
45
44
Description
Data Bus:
Data bus comprises eight TRI-STATE input/output lines. The bus provides
bidirectional communications between the UART and the CPU. Data, control words,
and status information are transferred via the D7-D0 Data Bus.
A2
A1
A0
I
15
14
10
10
9
4
Register Addresses:
Address signals connected to these 3 inputs select a DUART register for the CPU to
read from or write to during data transfer. Table 1 shows the registers and their
addresses. Note that the state of the Divisor Latch Access Bit (DLAB), which is the
most significant bit of the Line Control Register, affects the selection of certain
DUART registers. The DLAB must be set high by the system software to access the
Baud Generator Divisor Latches and the Alternate Function Register.
CS
I
18
13
Chip Select:
When CS is low, the chip is selected. This enables communication between the
DUART and the CPU. Valid chip select should stabilize according to the tAW
parameter.
CHSL
I
16
11
Channel Select:
CHSL directs the address and data information to the selected serial channel. (Table
1)
1 = channel 1 is selected.
0 = channel 2 is selected.
RD
I
24
20
IO Read:
The register data is placed on the D0 - D7 on the falling edge of RD. The CPU can
read status information or data from the selected DUART register on the rising edge.
WR
I
20
15
IO Write:
On the falling edge of WR, data is placed on the D0 - D7. On the rising edge, the data
is latched into the selected DUART register.
RXRDY1
RXRDY2
O
N/A
31
8
UART Receive-ready: The receiver DMA signaling is available through this pin which
is a seperate pin on the TQFP package, while on the PLCC package it is available
through the MF pins (19, 35). When operating in the FIFO mode, the CPU selects
one of two types of DMA transfer via FCR[3]. When operating in the 16450 Mode,
only DMA mode 0 is available. Mode 0 supports single transfer DMA (and a transfer is
usually made between CPU bus cycles). Mode 1 supports multi-transfer DMA where
multiple transfers are made continuously until the Rx FIFO is empty. Details regarding
the active and inactive states of this signal are described in Section 6.5 FIFO
CONTROL REGISTER (FCR) and Section 7.9 DMA OPERATION.
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NS16C2552/NS16C2752
5.0 Pin Descriptions
Signal
Name
Type
(Continued)
PLCC
Pin #
TQFP
Pin #
Description
TXRDY1
TXRDY2
O
1
32
43
28
UART Transmit-ready:
Transmitter DMA signaling is available through this pin. When operating in the FIFO
mode, the CPU selects one of two types of DMA transfer via FCR[3]. When operating
in the 16450 Mode, only DMA mode 0 is allowed. Mode 0 supports single transfer
DMA (and a transfer is usually made between CPU bus cycles). Mode 1 supports
multi-transfer DMA where multiple transfers are made continuously until the Tx FIFO
is full. Details regarding the active and inactive states of this signal are described in
Section 6.5 FIFO CONTROL REGISTER (FCR) and Section 7.9 DMA OPERATION.
INTR1
INTR2
O
34
17
30
12
Interrupt Output:
INTR goes high whenever any one of the following interrupt types has an active high
condition and is enabled via the IER: Receiver Error Flag; Received Data Available:
time-out (FIFO Mode only); Transmitter Holding Register Empty; MODEM Status; and
hardware and software flow control. The INTR signal is reset low upon the
appropriate interrupt service or a Master Reset operation.
5.2 SERIAL IO INTERFACE
Signal
Name
Type
PLCC
Pin #
TQFP
Pin #
SOUT1
O
38
35
UART Serial Data Out:
26
22
UART transmit data output or infrared data output. The SOUT signal is set to logic 1
upon reset or idle in the UART mode when MCR[6]=0. The SOUT signal transitions to
logic 0 (idle state of IrDA mode) in the infrared mode when MCR[6]=1.
SOUT2
Description
Note: SOUT1 and SOUT2 can not be reset to IrDA mode.
SIN1
SIN2
I
39
25
36
21
UART Serial Data In:
UART receive data input or infrared data input. The SIN should be idling in logic 1 in
the UART mode. The SIN should be idling in logic 0 in the infrared mode. The SIN
should be pulled high through a 10K resistor if not used.
RTS1
RTS2
O
36
23
33
18
UART Request-to-send:
When low, RTS informs the remote link partner that it is ready to receive data. The
RTS output signal can be set to an active low by writing “1” to MCR[1]. The RTS
output can also be configured in auto hardware flow control based on FIFO trigger
level. This pin stays logic 1 upon reset or idle (i.e., between data transfers). Loop
mode operation holds this signal in its inactive state.
DTR1
DTR2
O
37
27
34
23
UART Data-terminal-ready:
When low, DTR informs the remote link partner that the UART is ready to establish a
communications link. The DTR output signal can be set to an active low by writing “1”
to MCR[0]. This pin stays at logic 1 upon reset or idle. Loop mode operation holds this
signal to its inactive state.
CTS1
CTS2
I
40
28
38
24
UART Clear-to-send:
When low, CTS indicates that the remote link partner is ready to receive data. The
CTS signal is a modem status input and can be read for the appropriate channel in
MSR[4]. This bit reflects the complement of the CTS signal. MSR[0] indicates whether
the CTS input has changed state since the previous read of the MSR. CTS can also
be configured to perform auto hardware flow control.
Note: Whenever the CTS bit of the MSR changes state, an interrupt is generated if the MODEM Status
Interrupt is enabled.
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Signal
Name
DSR1
DSR2
Type
I
(Continued)
PLCC
Pin #
TQFP
Pin #
41
29
39
25
Description
UART Data-set-ready:
When low, DSR indicates that the remote link partner is ready to establish the
communications link. The DSR signal is a MODEM status input and can be read for
the appropriate channel in MSR[5]. This bit reflects the complement of the DSR
signal. MSR[1] indicates whether the DSR input has changed state since the previous
read of the MODEM Status Register.
Note: Whenever the DSR bit of the MSR changes state, an interrupt is generated if the MODEM Status
Interrupt is enabled.
DCD1
DCD2
I
42
30
40
26
UART Data-carrier-detect:
When low, DCD indicates that the data carrier has been detected by the remote link
partner. The DCD signal is a MODEM status input and can be read for the appropriate
channel in MSR[7]. This bit reflects the complement of the DCD signal. MSR[3]
indicates if the DCD input has changed state since the previous reading of the
MODEM Status Register. DCD has no effect on the receiver.
Note: Whenever the DCD bit of the MSR changes state, an interrupt is generated if the MODEM Status
Interrupt is enabled.
RI1
RI2
I
43
31
41
27
UART Ring-detector:
When low, RI indicates that a telephone ringing is active. The RI signal is a MODEM
status input and can be read for the appropriate channel in MSR[6]. This bit reflects
the complement of the RI signal. MSR[2] indicates whether the RI input signal has
changed state from low to high since the previous reading of the MSR.
Note: Whenever the RI bit of the MSR changes from a high to a low state, an interrupt is generated if the
MODEM Status Interrupt is enabled.
MF1
MF2
O
35
19
32
14
UART Multi-function Pin:
MF can be programmed for any one of three signal functions OUT2, BAUDOUT or
RXRDY. Bits 2 and 1 of the Alternate Function Register select which output signal will
be present on this pin. OUT2 is the default signal and it is selected immediately after
master reset or power-up.
The OUT2 can be set active low by programming bit 3 (OUT2) of the MCR to a logic
1. A Master Reset operation sets this signal to its inactive (high) state. Loop Mode
holds this signal in its inactive state.
The BAUDOUT signal is the 16X clock output that drives the transmitter and receiver
logic of the associated serial channel. This signal is the result of the XIN clock divided
by the value in the Divisor Latch Registers. The BAUDOUT signal for each channel is
internally connected to provide the receiver clock (formerly RCLK on the PC16550D).
The RXRDY signal can be used to request a DMA transfer of data from the RCVR
FIFO. Details regarding the active and inactive states of this signal are described in
Section 6.5 FIFO CONTROL REGISTER (FCR) and Section 7.9 DMA OPERATION.
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NS16C2552/NS16C2752
5.0 Pin Descriptions
NS16C2552/NS16C2752
5.0 Pin Descriptions
(Continued)
5.3 CLOCK AND RESET
Signal
Name
Type
PLCC
Pin #
TQFP
Pin #
XIN
I
11
5
External Crystal Input:
XIN input is used in conjunction with XOUT to form a feedback circuit for
the baud rate generator’s oscillator. If a clock signal is generated
off-chip, then it should drive the baud rate generator through this pin.
Refer to Section 7.1 CLOCK INPUT.
XOUT
O
13
7
External Crystal Output:
XOUT output is used in conjunction with XIN to form a feedback circuit
for the baud rate generator’s oscillator. If the clock signal is generated
off-chip, then this pin is unused. Refer to Section 7.1 CLOCK INPUT.
MR
I
21
16
Master Reset:
When MR input is high, it clears all the registers including Tx and Rx
serial shift registers (except the Receiver Buffer, Transmitter Holding,
and Divisor Latches). The output signals, such as OUT2, RTS, DTR,
INTR, and SOUT are also affected by an active MR input. (Refer to
Table 26 and Section 7.2 RESET).
Description
5.4 POWER AND GROUND
Signal
Name
Type
PLCC
Pin #
TQFP
Pin #
Description
VCC
I
33
44
29
42
VCC:
+2.97V to +5.5V supply.
GND
I
12
22
6
17
GND:
Device ground reference.
NC
I
N/A
19
37
No Connection:
These pins are only available on the TQFP package.
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8
There are two identical register sets, one for each channel,
in the DUART. All register descriptions in this section apply to
the register sets in both channels.
To clarify the descriptions of transmission and receiving operations, the nomenclatures through out this documentation
are as follows:
TABLE 1. Basic Register Addresses
DLAB1
C
H
A
N
N
E
L
1
C
H
A
N
N
E
L
2
CHSL
A2
A1
A0
Register
0
1
0
0
0
Receive Buffer (Read), Transmitter Holding Register
(Write)
0
1
0
0
1
Interrupt Enable
0
1
0
1
0
Interrupt Identification (Read)
0
1
0
1
0
FIFO Control (Write)
x
1
0
1
1
Line Control
x
1
1
0
0
Modem Control
x
1
1
0
1
Line Status (Read)
x
1
1
1
0
Modem Status (Read)
x
1
1
1
1
Scratchpad
1
1
0
0
0
Divisor Latch (Least Significant Byte)
1
1
0
0
1
Divisor Latch (Most Significant Byte)
Alternate Function
1
1
0
1
0
DLAB1
CHSL
A2
A1
A0
Register
0
0
0
0
0
Receive Buffer (Read), Transmitter Holding Register
(Write)
0
0
0
0
1
Interrupt Enable
0
0
0
1
0
Interrupt Identification (Read)
0
0
0
1
0
FIFO Control (Write)
x
0
0
1
1
Line Control
x
0
1
0
0
Modem Control
x
0
1
0
1
Line Status (Read)
x
0
1
1
0
Modem Status (Read)
x
0
1
1
1
Scratchpad
1
0
0
0
0
Divisor Latch (Least Significant Byte)
1
0
0
0
1
Divisor Latch (Most Significant Byte)
1
0
0
1
0
Alternate Function
9
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NS16C2552/NS16C2752
• Frame - Refers to all the bits between Start and Stop.
• Character or word - The payload of a frame, between 5 to
8 bits.
• “!=” - Not equal to.
• Res - Reserved bit.
The address and control pins to register selection is summarized in Table 1.
6.0 Register Set
NS16C2552/NS16C2752
6.0 Register Set
(Continued)
TABLE 2. NS16C2552 Register Summary
Reg
Addr
A2-A0
RD/
WR
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Comment
UART 16C550 Compatible Registers (Default Values Upon Reset)
RBR
THR
0x0
R/W
Data7
X
X
R/W
CTS Int
Ena
RTS
Int
Ena
0
0
0
0
0
0
0
0
R
FIFOs
Ena
FIFOs
Ena
INT
Src
Bit 5
INT Src
Bit 4
INT
Src
Bit 3
INT
Src
Bit 2
INT Src
Bit 1
INT Src
Bit 0
0
0
W
RX
FIFO
Trigger
0
0
0
0
0
0
0
0
R/W
Divisor
Ena
Set Tx
Break
Set
Parity
Even
Parity
Parity
Ena
Stop
Bits
Word
Length
Bit 1
Word
Length
Bit 0
0
0
0
0
0
0
0
0
R/W
Clk Div
Sel
IR Md
Ena
Xon
Any
Internal
Loopbk
Ena
OUT2
OUT1
RTS
Output
Control
DTR
Output
Control
0
0
0
0
0
0
0
0
Rx
FIFO
Gbl Err
THR &
TSR
Empty
THR E
mpty
Rx
Break
Rx
Frame
Error
Rx
Parity
Error
Rx Overrun
Error
Rx
Data
Ready
0
1
1
0
0
0
0
0
DCD
Input
RI
Input
DSR
Input
CTS
Input
Delta
DCD
Delta
RI
Delta
DSR
Delta
CTS
DCD
RI
DSR
CTS
0
0
0
0
Default
IER
0x1
Default
IIR
0x2
Default
FCR
0x2
0
Default
LCR
0x3
Default
MCR
0x4
Default
LSR
0x5
R
Default
MSR
0x6
R
Default
SCR
R/W
Data6
Data5
Data4
Data3
X
X
X
Xoff Int Sleep Md Modem
Ena
Ena
Stat Int
Ena
RX
Tx
FIFO
FIFO
Trigger Trigger
(2752)
Data2
Data1
Data0
X
X
X
RX
Line
Stat
Int
Ena
Tx Empty
Int Ena
Rx
Data Int
Ena
0
0
0
0
1
Tx FIFO
Trigger
(2752)
DMA
Md
Ena
Tx
FIFO
Reset
Rx FIFO
Reset
FIFOs
Ena
SCR
SCR
SCR
SCR
SCR
SCR
SCR
SCR
0x7
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
1
1
1
1
1
1
1
1
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10
LCR[7] = 0
LCR != 0xBF
(Continued)
TABLE 2. NS16C2552 Register Summary (Continued)
Reg
Addr
A2-A0
RD/
WR
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Comment
Baud Rate Generator Divisor
DLL
DLL
DLL
DLL
DLL
DLL
DLL
DLL
DLL
0x0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
X
X
X
X
X
X
X
X
DLM
DLM
DLM
DLM
DLM
DLM
DLM
DLM
0x1
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
X
X
X
X
X
X
X
X
Rsrvd
Rsrvd
Rsrvd
Rsrvd
Rsrvd RXRDY
BAUDOUT
Concurrent
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Sel
WR
DLM
AFR
R/W
R/W
R/W
0x2
Default
DREV
0x0
R
Sel
0
0
0
0
0
0
0
0
ID
Bit 7
ID
Bit 6
ID
Bit 5
ID
Bit 4
DREV
Bit 3
DREV
Bit 2
DREV
Bit 1
DREV
Bit 0
LCR[7] = 1
LCR ! 0xBF
LCR[7] = 1
LCR != 0xBF
DLL = 0x00
DLM = 0x00
Enhanced Registers
EFR
0x2
R/W
Auto
CTS
Ena
0
0
0
0
0
0
0
0
R/W
XON1
XON1
XON1
XON1
XON1
XON1
XON1
XON1
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
XON1
0x4
Default
XON2
R/W
0x5
Default
XOFF1
Special IER[7:4]
SW
SW
SW Flow
Char
IIR[5:4]
Flow
Flow Control Bit 1
Sel
FCR[5:4] Control Control
MCR[7:5] Bit 3
Bit 2
SW
Flow
Control
Bit 0
0
0
0
0
0
0
0
0
XON2
XON2
XON2
XON2
XON2
XON2
XON2
XON2
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
0
0
R/W
Auto
RTS
Ena
XOFF1
XOFF1 XOFF1
0
XOFF1
XOFF1 XOFF1
0
0
XOFF1
XOFF1
0x6
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Default
0
0
0
0
0
0
0
0
XOFF2
XOFF2
XOFF2
0x7
R/W
XOFF2
Bit 7
XOFF2 XOFF2
Bit 6
Bit 5
XOFF2
Bit 4
XOFF2 XOFF2
Bit 3
Bit 2
Bit 1
Bit 0
Default
0
0
0
0
0
0
0
0
Legend
Bit
Name
Default
Value
LCR = 0xBF
• n’bN - n is the number of bits; N is the bit value. Example
8’b01010111 = 8’h57 = 0x57.
The Nomenclature of register descriptions:
• Register name, address, register bit, and value example:
FCR 0x2.7:6 = 2’b11 - bits 6 and 7 of FCR are both 1.
Alternative description: FCR[7:6] = 2’b11.
6.1 RECEIVE BUFFER REGISTER (RBR)
The receiver section contains an 8-bit Receive Shift Register
(RSR) and a 16 (or 64)-byte FIFO that can be accessed
through Receive Buffer Register (RBR).
• ‘b - binary number.
• ‘h - hex number.
• 0xNN - hex number.
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NS16C2552/NS16C2752
6.0 Register Set
NS16C2552/NS16C2752
6.0 Register Set
(Continued)
TABLE 3. RBR (0x0)
Bit
Bit Name
R/W Def
7:0
RBR Data
R
0xXX
Description
Receive Buffer Register
Rx FIFO data.
Note: This register value does not change upon MR reset.
6.2 TRANSMIT HOLDING REGISTER (THR)
This register holds the byte-wide transmit data (THR). This is
a write-only register.
TABLE 4. THR (0x0)
Bit
Bit Name
R/W Def
7:0
THR Data
W
0xXX
Description
Transmit Holding Register
Tx FIFO data.
Note: This register value does not change upon MR reset.
6.3 INTERRUPT ENABLE REGISTER (IER)
sired to be used, masking an interrupt source prevents it
from going active in the IIR and activating the INTR output
signal. While interrupt sources are masked off, all system
functions including the Line Status and MODEM Status still
operate in their normal manner. Table 5 shows the contents
of the IER.
This register enables eight types of interrupts for the corresponding serial channel. Each interrupt source can individually activate the interrupt (INTR) output signal. Setting the
bits of the IER to a logic 1 unmasks the selected interrupt(s).
Similarly, the interrupt can be masked off by resetting bits 0
through 7 of the Interrupt Enable Register (IER). If not de-
TABLE 5. IER (0x1)
Bit
Bit Name
R/W
Def
7
CTS Int Ena
R/W
0
Description
CTS Input Interrupt Enable
1 = Enable the CTS to generate interrupt at low to high transition. Requires EFR 0x2.4 = 1.
0 = Disable the CTS interrupt (default).
6
RTS Int Ena
R/W
0
RTS Output Interrupt Enable
1 = Enable the RTS to generate interrupt at low to high transition. Requires EFR 0x2.4 = 1.
0 = Disable the RTS interrupt (default).
5
Xoff Int Ena
R/W
0
Xoff Input Interrupt Enable
1 = Enable the software flow control character Xoff to generate interrupt. Requires EFR
0x2.4 = 1.
0 = Disable the Xoff interrupt (default).
4
Sleep Mode
Ena
R/W
Mdm Stat Int
Ena
R/W
Rx Line Stat
Int Ena
R/W
0
Sleep Mode Enable
1 = Enable the Sleep Mode for the respective channel. Requires EFR 0x2.4 = 1.
0 = Disable Sleep Mode (default).
3
0
Modem Status Interrupt Enable
1 = Enable the Modem Status Register interrupt.
0 = Disable the Modem Status Register interrupt (default).
2
0
Receive Line Status Interrupt Enable
An interrupt can be generated when any of the LSR bits 0x5.4:1=1. LSR 0x5.1 generates
an interrupt as soon as an overflow frame is received. LSR 0x5.4:2 generate an interrupt
when there is read error from FIFO.
1 = Enable the receive line status interrupt.
0 = Disable the receive line status interrupt (default).
1
Tx_Empty Int
Ena
R/W
0
Tx Holding Reg Empty Interrupt Enable
1 = Enable the interrupt when Tx Holding Register is empty.
0 = Disable the Tx Holding Register from generating interrupt (default).
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NS16C2552/NS16C2752
6.0 Register Set
(Continued)
TABLE 5. IER (0x1) (Continued)
Bit
Bit Name
0
Rx_DV Int
Ena
R/W
Def
R/W
0
Description
Rx Data Available Interrupt Enable
1 = Enable the Received Data Available and FIFO mode time-out interrupt.
0 = Disable the Received Data Available interrupt (default).
6.4 INTERRUPT IDENTIFICATION REGISTER (IIR)
the associated DUART serial channel freezes all interrupts
and indicates the highest priority pending interrupt to the
CPU. While this CPU access is occurring, the associated
DUART serial channel records new interrupts, but does not
change its current indication until the access is complete.
Table 6 shows the contents of the IIR.
In order to provide minimum software overhead during data
word transfers, each serial channel of the DUART prioritizes
interrupts into seven levels and records these levels in the
Interrupt Identification Register. The seven levels of interrupt
conditions are listed in Table 7. When the CPU reads the IIR,
TABLE 6. IIR (0x2)
Bit
Bit Name
R/W
Def
7:6
FIFOs Ena
R
FIFO Enable Status (FCR 0x2.0)
00
2’b11 = Tx and Rx FIFOs enabled.
Description
2’b00 = Tx and Rx FIFOs disabled (default).
5
INT Src 5
R
RTS/CTS Interrupt Status
0
1 = RTS or CTS changed state from low to high.
0 = No change on RTS or CTS from low to high (default).
4
INT Src 4
R
Xoff or Special Character Interrupt Status
0
1 = Receiver detected Xoff or special character.
0 = No Xoff character match (default).
3:1
INT Src 3:1
R
Interrupt Source Status
000
0
INT Src 0
These three bits indicates the source of a pending interrupt. Refer to Table 7 for
interrupt source and priority.
R
Interrupt Status
1
1 = No interrupt is pending (default).
0 = An interrupt is pending and the IIR content may be used as a pointer for the
interrupt service routine.
TABLE 7. Interrupt Source and Priority Level
IIR Register Status Bits
Priority
Level
5
4
3
2
1
0
1
0
0
0
1
1
0
LSR
2
0
0
1
1
0
0
RXRDY (Receive data time-out)
3
0
0
0
1
0
0
RXRDY (Receive data ready)
4
0
0
0
0
1
0
TXRDY (Transmit data 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 state from low to high
-
0
0
0
0
0
1
None (default)
Interrupt Source
TABLE 8. Interrupt Sources and Clearing
Interrupt
Generation
LSR
Interrupt Sources
Interrupt Clearing
Any bit is set in LSR[4:1] (Break Interrupt,
Framing, Rx parity, or overrun error).
Read LSR register. (Interrupt flags and tags are not
cleared until the character(s) that generated the
interrupt(s) has/have been emptied or cleared.)
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NS16C2552/NS16C2752
6.0 Register Set
(Continued)
TABLE 8. Interrupt Sources and Clearing (Continued)
Interrupt
Generation
Interrupt Sources
Interrupt Clearing
Rx Trigger
Rx FIFO reached trigger level.
Read FIFO data until FIFO pointer falls below the
trigger level.
RXRDY
Timer
Time-out in 4-word time plus 12-bit delay time.
Read RBR.
TXRDY
THR empty.
Read from IIR register or a write to THR.
MSR
Any state change in MSR[3:0].
Read from MSR register.
Xoff or
Special
character
Detection of Xoff or Special character.
Read from IIR register or reception of Xon character
(or reception of next character if interrupt is caused by
Special character).
CTS
Input pin toggles from logic 0 to 1 during CTS
auto flow control mode.
Read from IIR or MSR.
RTS
Output pin toggles from logic 0 to 1 during RTS
auto flow control mode.
Read from IIR or MSR.
Mode 1: Mode 1 allows for multiple transfer or multicharacter burst transfer. In the FIFO Mode (FCR[0] = 1,
FCR[3] = 1) when the number of characters in the RCVR
FIFO equals the trigger threshold level or timeout occurs, the
RXRDY goes active low to initiate DMA transfer request. The
RXRDY returns high when RCVR FIFO becomes empty.
In the FIFO Mode (FCR[0] = 1, FCR[3] = 1) when there is (1)
no character in the XMIT FIFO for NS16C2552, or (2) empty
spaces exceed the threshold level for NS16C2752; the
TXRDY pin will go active low. This pin will become inactive
when the XMIT FIFO is completely full.
6.5 FIFO CONTROL REGISTER (FCR)
This is a write only register at the same location as the IIR
(the IIR is a read only register). This register is used to
enable the FIFOs, clear the FIFOs, set the FIFO trigger level,
and select the DMA mode.
Mode 0: Mode 0 allows for single transfer in each DMA
cycle. When in the 16450 Mode (FCR[0] = 0) or in the FIFO
Mode (FCR[0] = 1, FCR[3] = 0) and there is at least one
character in the RCVR FIFO or RCVR Buffer Register, the
RXRDY pin will go active low. After going active, the RXRDY
pin will be inactive when there is no character in the FIFO or
Buffer Register.
On The Tx side, TXRDY is active low when XMIT FIFO or
XMIT Holding Register is empty. TXRDY returns to high
when XMIT FIFO or XMIT holding register is not empty.
TABLE 9. FCR (0x2)
Bit
Bit
Name
R/W
Def
7:6
Rx FIFO
W
Rx FIFO Trigger Select
Trig
Select
00
FCR[6] and FCR[7] are used to designate the interrupt trigger level. When the number of
characters in the RCVR FIFO equals the designated interrupt trigger level, a Received Data
Available Interrupt is activated. This interrupt must be enabled by IER[0]=1.
Description
For NS16C2552 with 16-byte FIFO:
FCR[7]
FCR[6]
Rx FIFO Trigger Level
1
1
= 14
1
0
=8
0
1
=4
0
0
= 1 (Default)
For NS16C2752 with 64-byte FIFO:
FCR[7]
FCR[6]
Rx FIFO Trigger Level
1
1
= 60
1
0
= 56
0
1
= 16
0
0
= 8 (Default)
Refer to Section 7.5 SOFTWARE XON/XOFF FLOW CONTROL and Section 7.9 DMA
OPERATION for software flow control using FIFO trigger level.
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14
(Continued)
TABLE 9. FCR (0x2) (Continued)
Bit
5:4
Bit
Name
R/W
Def
Tx FIFO
Trig
Level Sel
W
Transmit FIFO Trigger Level Selection
00
The transmit FIFO trigger threshold selection is only available in NS16C2752. When
enabled, a transmit interrupt is generated and TXRDY is asserted when the number of empty
spaces in the FIFO exceeds the threshold level.
Description
For NS16C2752 with 64-byte FIFO:
FCR[5]
FCR[4]
Tx FIFO Trigger Level
1
1
= 56
1
0
= 32
0
1
= 16
0
0
= 8 (Default)
Refer to Section 7.4 TRANSMIT OPERATION and Section 7.9 DMA OPERATION for
transmit FIFO descriptions.
These two bits are reserved in NS16C2552 and have no impact when they are written to.
3
DMA
Mode
Select
W
DMA Mode Select
0
This bit controls the RXRDY and TXRDY initiated DMA transfer mode.
Tx FIFO
Reset
W
Transmit FIFO Reset
0
This bit is only active when FCR bit 0 = 1.
1 = DMA Mode 1. Allows block transfers. Requires FCR 0x2.0=1 (FIFO mode).
0 = DMA Mode 0 (default). Single transfers.
2
1 = Reset XMIT FIFO pointers and all bytes in the XMIT FIFO (the Tx shift register is not
cleared and is cleared by MR reset). This bit has the self-clearing capability.
0 = No impact (default).
Note: Reset pointer will cause the characters in Tx FIFO to be lost.
1
Rx FIFO
Reset
W
Receive FIFO Reset
0
This bit is only active when FCR bit 0 = 1.
1 = Reset RCVR FIFO pointers and all bytes in the RCVR FIFO (the Rx shift register is not
cleared and is cleared by MR reset). This bit has the self-clearing capability.
0 = No impact (default).
Note: Reset pointer will cause the characters in Rx FIFO to be lost.
0
Tx and
Rx FIFO
Enable
W
Transmit and Receive FIFO Enable
0
1 = Enable transmit and receive FIFO. This bit must be set before other FCR bits are
written. Otherwise, the FCR bits can not be programmed.
0 = Disable transmit and receive FIFO (default).
15
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NS16C2552/NS16C2752
6.0 Register Set
NS16C2552/NS16C2752
6.0 Register Set
sor Latch Access bit via the Line Control Register (LCR).
This is a read and write register.
(Continued)
6.6 LINE CONTROL REGISTER (LCR)
The system programmer specifies the format of the asynchronous data communications exchange and sets the DiviTABLE 10. LCR (0x3)
Bit
Bit Name
Default
R/W
Def
7
Divisor Latch
R/W
Ena
0
Tx Break
Ena
R/W
6
0
Description
Divisor Latch Access Bit (DLAB)
This bit must be set (logic 1) to access the Divisor Latches of the Baud Generator
and the Alternate Function Register during a read or write operation. It must be
cleared (logic 0) to access any other register.
1 = Enable access to the Divisor Latches of the Baud Generator and the AFR.
0 = Enable access to other registers (default).
Set Tx Break Enable
This bit is the Break Control bit. It causes a break condition to be transmitted to the
receiving UART. The Break Control bit acts only on SOUT and has no effect on the
transmitter logic.
1 = Serial output (SOUT) is forced to the Spacing State (break state, logic 0).
0 = The break transmission is disabled (default).
Note: This feature enables the CPU to alert a terminal in a computer communication
system. If the following sequence is followed, no erroneous or extraneous character
will be transmitted because of the break.
1. Load an all 0s, pad character, in response to THRE.
2. Set break after the next THRE.
3. Wait for the transmitter to be idle, (Transmitter Empty TEMT = 1), and clear break
when normal transmission has to be restored.
During the break, the transmitter can be used as a character timer to establish the
break duration.
During the break state, any word left in THR will be shifted out of the register but
blocked by SOUT as forced to break state. This word will be lost.
5
4
Forced
Parity Sel
Even/Odd
Parity Sel
R/W
0
R/W
0
Tx and Rx Forced Parity Select
When parity is enabled, this bit selects the forced parity format.
LCR[5]
LCR[4]
LCR[3]
1
1
1
Force parity to space = 0
Parity Select
1
0
1
Force parity to mark = 1
0
1
1
Even parity
0
0
1
Odd parity
X
X
0
No parity
Tx and Rx Even/Odd Parity Select
This bit is only effective when LCR[3]=1. This bit selects even or odd parity format.
1 = Odd parity is transmitted or checked.
0 = Even parity is transmitted or checked (default).
3
Tx/Rx Parity
Ena
R/W
0
Tx and Rx Parity Enable
This bit enables parity generation.
1 = A parity is generated during the data transmission. The receiver checks for parity
error of the data received.
0 = No parity (default).
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(Continued)
TABLE 10. LCR (0x3) (Continued)
Bit
2
Bit Name
Default
R/W
Def
Tx/Rx
Stop-bit
Length Sel
R/W
0
Description
Tx and Rx Stop-bit Length Select
This bit specifies the number of Stop bits transmitted with each serial character.
LCR[2]
Word Length Sel
Stop-bit Length
1
6,7,8
=2
1
5
= 1.5
0
5,6,7,8
= 1(Default)
Stop-bit length is measured in bit time.
1:0
Tx/Rx Word
Length Sel
R/W
0
Tx and Rx Word Length Select
These two bits specify the word length to be transmitted or received.
LCR[1]
LCR[0]
1
1
=8
1
0
=7
0
1
=6
0
0
= 5 (Default)
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Word Length
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NS16C2552/NS16C2752
6.0 Register Set
NS16C2552/NS16C2752
6.0 Register Set
clock divider for each channel. Each is capable of taking a
common clock input from DC to 80 MHz and dividing the
clock frequency by 1 (default) or 4 depending on the MCR[7]
value. The clock divider and the internal clock division flow is
shown in Figure 1.
(Continued)
6.7 MODEM CONTROL REGISTER (MCR)
This register controls the interface with the MODEM or data
set (or a peripheral device emulating a MODEM). There is a
20204803
FIGURE 1. Internal Clock Dividers
TABLE 11. MCR (0x4)
Bit
Bit Name
7
Clk Divider
Sel
R/W
Def
R/W
0
Description
Clock Divider Select
This bit selects the clock divider from crystal or oscillator input. The divider output
connects to the Baud Rate Generator.
1 = Divide XIN frequency by 4.
0 = Divide XIN frequency by 1 (default).
6
IR Mode
Sel
R/W
0
Infrared Encoder/Decoder Select
This bit selects standard modem or IrDA interface.
1 = Infrared IrDA Tx/Rx. The data input and output levels complies to the IrDA infrared
interface. The Tx output is at logic 0 during the idle state.
0 = Standard modem Tx/Rx (default).
5
Xon-Any
Ena
R/W
0
Xon-Any Enable
This bit enables Xon-Any feature.
1 = Enable Xon-Any function. When Xon/Xoff flow control is enabled, the transmission
resumes when any character is received. The received character is loaded into the Rx
FIFO except for Xon or Xoff characters.
0 = Disable Xon-Any function (default).
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(Continued)
TABLE 11. MCR (0x4) (Continued)
Bit
Bit Name
4
Internal
Loopback
Ena
R/W
Def
R/W
0
Description
Internal Loopback Enable
This bit provides a local loopback feature for diagnostic testing of the associated serial
channel. (Refer to Section 7.8 INTERNAL LOOPBACK MODE and Figure 13.)
1 = the transmitter Serial Output (SOUT) is set to the Marking (logic 1) state; the
receiver Serial Input (SIN) is disconnected; the output of the Transmitter Shift Register is
looped back into the Receiver Shift Register input; the four MODEM Control inputs
(DSR, CTS, RI, and DCD) are disconnected; the four MODEM Control outputs (DTR,
RTS, OUT1 and OUT2) are internally connected to the four MODEM Control inputs; and
the MODEM Control output pins are forced to their inactive state (high). In this
diagnostic mode, data that is transmitted is immediately received. This feature allows the
processor to verify transmit and receive data paths of the DUART. In this diagnostic
mode, the receiver and transmitter interrupts are fully operational. Their sources are
external to the part. The MODEM Control Interrupts are also operational, but the
interrupt sources are now the lower four bits of the MODEM Control Register instead of
the four MODEM Control inputs. The interrupts are still controlled by the Interrupt Ena
0 = Normal Tx/Rx operation; loopback disabled (default).
3
OUT2
R/W
0
Output2
This bit controls the Output 2 (OUT2) signal, which is an auxiliary user-designated
output. Bit 3 affects the OUT2 pin as described below. The function of this bit is
multiplexed on a single output pin with two other functions: BAUDOUT and RXDRY. The
OUT2 function is the default function of the pin after a master reset. See Section 6.12
ALTERNATE FUNCTION REGISTER (AFR) for more information about selecting one of
these 3 pin functions.
1 = Force OUT2 to logic 0.
0 = Force OUT2 to logic 1 (default).
2
OUT1
R/W
0
Output1
In normal operation, OUT1 bit is not available as an output.
In internal Loopback Mode (MCR 0x4.4=1) this bit controls the state of the modem input
RI in the MSR bit 6.
1 = MSR 0x06.6 is at logic 1.
0 = MSR 0x06.6 is at logic 0.
1
RTS
Output
R/W
0
RTS Output Control
This bit controls the RTS pin. If modem interface is not used, this output is used as a
general purpose output.
1 = Force RTS pin to logic 0.
0 = Force RTS pin to logic 1(default).
0
DTR
Output
R/W
0
DTR Output Control
This bit controls the DTR pin. If modem interface is not used, this output is used as a
general purpose output.
1 = Force DTR pin to logic 0.
0 = Force DTR pin to logic 1(default).
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NS16C2552/NS16C2752
6.0 Register Set
NS16C2552/NS16C2752
6.0 Register Set
Bits 1 through 4 are the error conditions that produce a
Receiver Line Status interrupt whenever any of the corresponding conditions are detected and the interrupt is enabled.
(Continued)
6.8 LINE STATUS REGISTER (LSR)
This register provides status information to the CPU concerning the data transfer.
TABLE 12. LSR (0x5)
Bit
Bit Name
R/W
Def
7
Rx FIFO Err
R
Rx FIFO Data Error
0
This bit is a global Rx FIFO error flag. In the 16450 Mode this bit is 0.
Description
1 = A sum of all error bits in the Rx FIFO. These errors include parity, framing, and
break indication in the FIFO data.
0 = No Rx FIFO error (default).
Note: The Line Status Register is intended for read operations only. Writing to this register is not recommended
as this operation is only used for factory testing.
6
THR & TSR
Empty
R
THR and TSR Empty
1
This bit is the Transmitter Empty (TEMT) flag.
1 = Whenever the Transmitter Holding Register (THR) (or the Tx FIFO in FIFO mode)
and the Transmitter Shift Register (TSR) are both empty (default).
0 = Whenever either the THR (or the Tx FIFO in FIFO mode) or the TSR contains a
data word.
5
THR Empty
R
THR Empty
1
This bit is the Transmitter Holding Register Empty (THRE) flag. In the 16450 mode bit
5 indicates that the associated serial channel is ready to accept a new character for
transmission. In addition, this bit causes the DUART to issue an interrupt to the CPU
when the Transmit Holding Register Empty interrupt enable is set.
1 = In 16450 mode, whenever a character is transferred from the Transmitter Holding
Register into the Transmitter Shift Register, or in FIFO mode when the Tx FIFO is
empty (default).
0 = In 16450 mode, this bit is reset to logic 0 concurrently with the loading of the
Transmitter Holding Register by the CPU. In FIFO mode, it is cleared when at least 1
byte is written to the Tx FIFO.
4
Rx Break
Interrupt
R
Receive Break Interrupt Indicator
0
This bit is the Break Interrupt (BI) indicator.
1 = Whenever the received data input is held in the Spacing (logic 0) state for longer
than a full frame transmission time (that is, the total time of Start bit + data bits +
Parity + Stop bits).
0 = No break condition (default).
This bit is reset to 0 whenever the CPU reads the contents of the Line Status Register
or when the next valid character is loaded into the Receiver Buffer Register.
In the FIFO Mode this condition is associated with the particular character in the FIFO
it applies to. It is revealed to the CPU when its associated character is at the top of
the FIFO. When break occurs only one zero character is loaded into the FIFO. The
next character transfer is enabled after SIN goes to the Marking (logic 1) state and
receives the next valid start bit.
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(Continued)
TABLE 12. LSR (0x5) (Continued)
Bit
Bit Name
3
Rx Frame
Error
R/W
Def
Description
R
Framing Error Indicator
0
This bit is the Framing Error (FE) indicator.
1= Received character did not have a valid Stop bit when the serial channel detects a
logic 0 during the first Stop bit time.
0 = No frame error (default).
The bit is reset to 0 whenever the CPU reads the contents of the Line Status Register
or when the next valid character is loaded into the Receiver Buffer Register. In the
FIFO Mode this error is associated with the particular character in the FIFO it applies
to. This error is revealed to the CPU when its associated character is at the top of the
FIFO. The serial channel will try to resynchronize after a framing error. This assumes
that the framing error was due to the next start bit, so it samples this start bit twice
and then takes in the data.
2
Rx Parity
Error
R
Parity Error Indicator
0
This bit is the Parity Error (PE) indicator.
1 = Received data word does not have the correct even or odd parity, as selected by
the even-parity-select bit during the character Stop bit time when the character has a
parity error.
0 = No parity error (default).
This bit is reset to a logic 0 whenever the CPU reads the contents of the Line Status
Register or when the next valid character is loaded into the Receiver Buffer Register.
In the FIFO mode this error is associated with the particular character in the FIFO it
applies to. This error is revealed to the host when its associated character is at the
top of the FIFO.
1
Rx Overrun
Error
R
0
Overrun Error Indicator
This bit is the Overrun Error (OE) indicator.
This bit indicates that the next character received was transferred into the Receiver
Buffer Register before the CPU could read the previously received character. This
transfer overwrites the previous character. It is reset whenever the CPU reads the
contents of the Line Status Register. If the FIFO mode data continues to fill the FIFO
beyond the trigger level, an overrun error will occur only after the FIFO is full and the
next character has been completely received in the shift register. OE is indicated to
the CPU as soon as it happens. The character in the shift register can be overwritten,
but it is not transferred to the FIFO.
1 = Set to a logic 1 during the character stop bit time when the overrun condition
exists.
0 = No overrun error (default).
0
Rx Data
Ready
R
0
Receiver Data Indicator
This bit is the receiver Data Ready (DR) indicator.
1 = Whenever a complete incoming character has been received and transferred into
the Receiver Buffer Register (RBR) or the FIFO. Bit 0 is reset by reading all of the
data in the RBR or the FIFO.
0 = No receive data available (default).
21
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NS16C2552/NS16C2752
6.0 Register Set
NS16C2552/NS16C2752
6.0 Register Set
addition to this current-state information, four bits of the
MODEM Status Register provide change information. The
latter bits are set to a logic 1 whenever a control input from
the MODEM changes state. They are reset to logic 0 whenever the CPU reads the MODEM Status Register.
(Continued)
6.9 MODEM STATUS REGISTER (MSR)
This register provides the current state of the control lines
from the MODEM (or peripheral device) to the CPU. In
TABLE 13. MSR (0x6)
R/W
Def
Bit
Bit Name
7
DCD Input
R
Status
DCD
RI Input
Status
R
RI Input Status
RI
This bit is the complement of the Ring Indicator (RI) input. In the loopback mode, this bit is
equivalent to OUT1 of the MCR.
6
Description
DCD Input Status
This bit is the complement of the Data Carrier Detect (DCD) input. In the loopback mode,
this bit is equivalent to the OUT2 of the MCR.
1 = DCD input is logic 0.
0 = DCD input is logic 1.
1 = RI input is logic 0.
0 = RI input is logic 1.
5
DSR Input
Status
R
DSR
DSR Input Status
This bit is the complement of the Data Set Ready (DSR) input. In the loopback mode, this
bit is equivalent to DTR in the MCR.
1 = DSR input is logic 0.
0 = DSR input is logic 1.
4
CTS Input
Status
R
CTS
CTS Input Status
This bit is the complement of the Clear to Send (CTS) input. In the loopback mode, this bit
is equivalent to RTS in the MCR.
1 = CTS input is logic 0.
0 = CTS input is logic 1.
3
DDCD
Input
Status
R
Delta DCD Input Indicator
0
This bit is the Delta Data Carrier Detect (DDCD) indicator. Bit 3 indicates that the DCD
input has changed state since the last read by the host.
1 = DCD input has changed state.
0 = DCD input has no state change (default).
Note: Whenever bit 0, 1, 2, or 3 is set to logic 1, a MODEM Status Interrupt is generated.
2
Falling
Edge RI
Indicator
R
Falling Edge RI Indicator
0
This bit is theFalling Edge of Ring Indicator (TERI) detector. Bit 2 indicates that the RI
input pin has changed from a logic 0 to 1 since the last read by the host.
1 = RI input has changed state from logic 0 to 1.
0 = RI input has no state change from 0 to 1 (default).
1
DDSR
Input
Indicator
R
Delta DSR Input Indicator
0
This bit is the Delta Data Set Ready (DDSR) indicator. Bit 1 indicates that the DSR input
pin has changed state since the last read by the host.
1 = DSR input has changed state from logic 0 to 1.
0 = DSR input has no state change from 0 to 1 (default).
0
DCTS
Input
Indicator
R
Delta CTS Input Indicator
0
This bit is the Delta Clear to Send (DCTS) indicator. Bit 0 indicates that the CTS input pin
has changed state since the last time it was read by the host.
1 = CTS input has changed state.
0 = CTS input has no state change (default).
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22
NS16C2552/NS16C2752
6.0 Register Set
(Continued)
6.10 SCRATCHPAD REGISTER (SCR)
This 8-bit Read/Write Register does not control the serial
channel in any way. It is intended as a Scratchpad Register
to be used by the programmer to hold data temporarily.
TABLE 14. SCR (0x7)
Bit
R/W
Def
Bit Name
7:0
Description
Scratchpad Register
This 8-bit register does not control the UART in any way. It is intended as a
scratchpad register to be used by the programmer to hold temporary data.
R/W
0xFF
SCR Data
6.11 PROGRAMMABLE BAUD GENERATOR
The NS16C2552 contains two independently programmable
Baud Generators. Each is capable of taking prescaler input
and dividing it by any divisor from 1 to 216 -1 (Figure 1). The
highest input clock frequency recommended with a divisor =
1 is 80MHz. The output frequency of the Baud Generator is
16 X the baud rate, [divisor # = (frequency input) / (baud rate
X 16)]. The output of each Baud Generator drives the transmitter and receiver sections of the associated serial channel.
Two 8-bit latches per channel store the divisor in a 16-bit
binary format. These Divisor Latches must be loaded during
initialization to ensure proper operation of the Baud Generator. Upon loading either of the Divisor Latches, a 16-bit Baud
Counter is loaded.
TABLE 15. DLL (0x0, LCR[7] = 1, LCR != 0xBF)
Bit
7:0
Bit Name
DLL Data
R/W
Def
Description
Divisor Latch LSB
This 8-bit register holds the least significant byte of the 16-bit baud rate generator divisor.
R/W
0xXX
Note: This register value does not change upon MR reset.
TABLE 16. DLM (0x1, LCR[7] = 1, LCR != 0xBF)
Bit
7:0
Bit Name
DLM Data
R/W
Def
Description
Divisor Latch MSB
This 8-bit register holds the most significant byte of the 16-bit baud rate generator divisor.
R/W
0xXX
Note: This register value does not change upon MR reset.
Table 17 provides decimal divisors to use with crystal frequencies of 1.8432 MHz, 3.072 MHz and 18.432 MHz. For
baud rates of 38400 and below, the error obtained is mini-
mal. The accuracy of the desired baud rate is dependent on
the crystal frequency chosen. Using a divisor of zero is not
recommended.
TABLE 17. Baud Rate Generation Using 1.8432 MHz Clock with MCR[7]=0
Output Data
Baud Rate
Output 16x Clock
Divider (dec)
User 16x Clock
Divisor (hex)
DLM Program
Value (hex)
DLL Program
Value (hex)
Data Rate
Error (%)
50
2304
900
09
00
0
75
1536
600
06
00
0
150
768
300
03
00
0
300
384
180
01
80
0
600
192
C0
00
C0
0
1200
96
60
00
60
0
2400
48
30
00
30
0
4800
24
18
00
18
0
9600
12
0C
00
0C
0
19,200
6
06
00
06
0
38,400
3
03
00
03
0
115,200
1
01
00
01
0
Note: For baud rates of 250k, 300k, 375k, 500k, 750k and 1.5M using a
24MHz crystal causes minimal error.
23
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NS16C2552/NS16C2752
6.0 Register Set
(Continued)
6.12 ALTERNATE FUNCTION REGISTER (AFR)
This is a read/write register used to select simultaneous
write to both register sets and alter MF pin functions.
TABLE 18. AFR (0x2, LCR[7] = 1, LCR != 0xBF)
Bit
Bit Name
Default
7:3
Reserved
2:1
MF Output Sel
R/W
Def
Description
Reserved
These bits are set to a logic 0.
R/W
0
0
Concurrent
Write Ena
Multi-function Pin Output Select
These select the output signal that will be present on the multi-function pin, MF.
These bits are individually programmable for each channel, so that different signals
can be selected on each channel.
R/W
0
AFR[2]
AFR[1]
1
1
MF Function
= Reserved (MF output is forced logic 1)
1
0
= RXRDY
0
1
= BAUDOUT
0
0
= OUT2 (default)
Concurrent Write Enable
1 = CPU can write concurrently to the same register in both registers sets. This
function is intended to reduce the DUART initialization time. It can be used by a CPU
when both channels are initialized to the same state. The CPU can set or clear this bit
by accessing either register set. When this bit is set the channel select pin still selects
the channel to be accessed during read operations. Setting or clearing this bit has no
effect on read operations.
The user should ensure that the DLAB bit LCR[7] of both channels are in the same
state before executing a concurrent write to register addresses 0, 1 and 2.
0 = No concurrent write (default). (No impact on read operations.)
6.13 DEVICE IDENTIFICATION REGISTER (ID)
The device ID for NS16C2552 is 0x03. DLL and DLM should
be initialized to 0x00 before reading the ID register. This is a
read-only register.
TABLE 19. DREV (0x0, LCR[7]=1, LCR!=0xBF, DLL=DLM=0x00)
Bit
Bit Name
R/W
Def
7:4
Device ID
R
Device ID
Value = 0x3 for NS16C2552; 0x2 for NS16C2752
3:0
Device Rev
R
Device Revision
Value = 0x1.
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Description
24
NS16C2552/NS16C2752
6.0 Register Set
(Continued)
6.14 ENHANCED FEATURE REGISTER (EFR)
This register enables the enhanced features of the device.
TABLE 20. EFR (0x2, LCR = 0xBF)
Bit
Bit Name
Default
R/W
Def
7
Auto CTS
R/W
Flow Ctl
Ena
0
Auto RTS
Flow Ctl
Ena
R/W
Description
Automatic CTS Flow Control Enable
1 = Enable automatic CTS flow control. Data transmission stops when CTS input deasserts to
logic 1. Data transmission resumes when CTS returns to logic 0.
0 = Automatic CTS flow control is disabled (Default)
6
0
Automatic RTS Flow Control Enable
By setting EFR[6] to logic 1, RTS output can be used for hardware flow control. When Auto
RTS is selected, an interrupt is generated when the receive FIFO is filled to the programmed
trigger level and RTS de-asserts to a logic 1. The RTS output must be logic 0 before the auto
RTS can take effect. RTS pin functions as a general purpose output when hardware flow
control is disabled.
1 = Enable automatic RTS flow control.
0 = Automatic RTS flow control is disabled (Default)
5
Special
Char Det
Ena
R/W
Enhanced
Fun Bit
Ena
R/W
0
Special Character Detect Enable
1 = Special character detect enabled. The UART compares each incoming received character
with data in Xoff-2 register (0x4, LCR = 0xBF). If a match is found, the received data will be
transferred to FIFO and IIR[4] is set to indicate the detection of a special character if IER[5] =
1. Bit 0 corresponds with the LSB of the received character. If flow control is set for
comparing Xon1, Xoff1 (EFR[1:0] = 10) then flow control and special character work normally;
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 IER[5] is enabled. Special character interrupts are cleared automatically
after the next received character.
0 = Special character detect disabled. (Default)
4
0
Enhanced Function Bits Enable
This bit enables IER[7:4], FCR[5:4], and MCR [7:5] to be changed. After changing the
enhanced bits, EFR[4] can be cleared to logic 0 to latch in the updated values. EFR[4] allows
compatibility with the legacy mode software by disabling alteration of the enhanced functions.
1 = Enables writing to IER[7:4], FCR[5:4], and MCR [7:5].
0 = Disable writing to IER[7:4], FCR[5:4], MCR [7:5] and, latching in updated value. Upon
reset, IER[7:4], IIR[5:4], FCR[5:4], and MCR [7:5] are cleared to logic 0. (Default)
25
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NS16C2552/NS16C2752
6.0 Register Set
(Continued)
TABLE 20. EFR (0x2, LCR = 0xBF) (Continued)
Bit
3:0
Bit Name
Default
R/W
Def
Software
Flow
Control
Sel
R/W
0
Description
Software Flow Control Select
Single character and dual sequential character software flow control is supported.
Combinations of software flow control can be selected by programming the bits.
EFR[3]
EFR[2]
EFR[1]
EFR[0]
1
1
1
0
1
1
Rx compares Xon1 or Xon2, Xoff1 or Xoff2
0
1
1
1
Rx compares Xon1 or Xon2, Xoff1 or Xoff2
0
0
1
1
Rx compares Xon1 & Xon2, Xoff1 & Xoff2
X
X
1
0
Rx compares Xon1, Xoff1
X
X
0
1
Rx compares Xon2, Xoff2
X
X
0
0
No Rx flow control
0
0
0
0
No Tx & Rx flow control (default)
EFR[3]
EFR[2]
1
Rx Flow Control
1
EFR[1]
EFR[0]
Rx compares Xon1 & Xon2, Xoff1 & Xoff2
Tx Flow Control
1
1
X
X
Tx Xon1 and Xon2, Xoff1 and Xoff2
1
0
X
X
Tx Xon1, Xoff1
0
1
X
X
Tx Xon2, Xoff2
0
0
X
X
No Tx flow control
6.15 SOFTWARE FLOW CONTROL REGISTERS (SFR)
The following four registers are used as programmable software flow control characters.
TABLE 21. Xon1 (0x4, LCR=0xBF)
Bit
7:0
Bit Name
Xon1 Data
R/W
Def
R/W
0
Description
Xon1 Data
TABLE 22. Xon2 (0x5, LCR=0xBF)
Bit
Bit Name
7:0
Xon2 Data
R/W
Def
R/W
0
Description
Xon2 Data
TABLE 23. Xoff1 (0x6, LCR=0xBF)
Bit
7:0
Bit Name
Xoff1 Data
R/W
Def
R/W
0
Description
Xoff1 Data
TABLE 24. Xoff2 (0x7, LCR=0xBF)
Bit
7:0
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Bit Name
Xoff2 Data
R/W
Def
R/W
0
Description
Xoff2 Data
26
NS16C2552/NS16C2752
7.0 Operation and Configuration
7.1 CLOCK INPUT
The NS16C2552/2752 has an on-chip oscillator that accepts
standard crystal with parallel resonant and fundamental frequency. The generated clock is supplied to both UART channels with the capability range from DC to 24 MHz. The
frequency of the clock oscillator is divided by 16 internally,
combined with an on-chip programmable clock divider providing the baud rate for data transmission. The divisor is
16-bit with MSB byte in DLM and LSB byte in DLL. The
divisor calculation is shown in Section 6.11 PROGRAMMABLE BAUD GENERATOR.
The external oscillator circuitry requires two load capacitors,
a parallel resistor, and an optional damping resistor. The
oscillator circuitry is shown in Figure 2.
20204805
FIGURE 3. Clock Input Circuitry
7.2 RESET
The NS16C2552/2752 has an on-chip power-on reset. An
external active high reset can also be applied. The default
output state of the device is listed in Table 26.
TABLE 26. Output State After Reset
Output
Reset State
SOUT1, SOUT2
Logic 1
OUT2
Logic 1
RTS1, RTS2
Logic 1
DTR1, DTR2
Logic 1
INTR1, INTR2
Logic 0
TXRDY1, TXRDY2
Logic 0
20204804
7.3 RECEIVER OPERATION
Each serial channel consists of an 8-bit Receive Shift Register (RSR) and a 16 (or 64) -byte by 11-bit wide Receive
FIFO. The RSR contains a 8-bit Receive Buffer Register
(RBR) that is part of the Receive FIFO. The 11-bit wide FIFO
contains an 8-bit data field and a 3-bit error flag field. The
RSR uses 16X clock as timing source. (Figure 4.)
FIGURE 2. Crystal Oscillator Circuitry
The requirement of the crystal is listed in Table 25.
TABLE 25. Crystal Component Requirement
Parameter
Crystal Frequency Range
Crystal Type
Value
< = 24 MHz
Parallel resonant
Fundamental
C1 & C2, Load Capacitance
10 - 22 pF
ESR
20 - 120 Ω
Frequency Stability 0 to 70˚C
100 ppm
The capacitors C1 and C2 are used to adjust the load
capacitance on these pins. The total load capacitance (C1,
C2 and crystal) must be within a certain range for the
NS16C2552/2752 to function properly. The parallel resistor
Rp and load resistor Rs are recommended by some crystal
vendors. Refer to the vendor’s crystal datasheet for details.
Since each channel has a separate programmable clock
divider, each channel can have a different baud rate.
The oscillator provides clock to the internal data transmission circuitry, writing and reading from the parallel bus is not
affected by the oscillator frequency. For circuits not using the
external crystal, the clock input is XIN (Figure 3.)
27
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NS16C2552/NS16C2752
7.0 Operation and Configuration
Character delay time is calculated by using the BAUDOUT
signal as a clock signal. This makes the delay proportional to
the baud rate.
(Continued)
Time-out interrupt is cleared and the timer is reset when the
CPU reads one character from the Receive FIFO. When the
time-out interrupt is inactive the time-out timer is reset after a
new character is received or after the CPU reads the Receive FIFO.
After the first character is read by the host, the next character is loaded into the RBR and the error flags are loaded into
LSR[4:2].
DMA Mode
In the FIFO mode, the RXRDY asserts when the character in
the Rx FIFO reaches the trigger threshold or timeout occurs.
The RXRDY initiates DMA transfer in a burst mode. The
RXRDY deasserts when the Rx FIFO is completely emptied
and the DMA transfer stops (Figure 5.)
20204806
FIGURE 4. Rx FIFO Mode
The RSR operation is described as follows:
1. At the falling edge of the start bit, an internal timer starts
counting at 16X clock. At 8th 16X clock, approximately
the middle of the start bit, the logic level is sampled. If a
logic 0 is detected the start bit is validated.
2. The validation logic continues to detect the remaining
data bits and stop bit to ensure the correct framing. If an
error is detected, it is reported in LSR[4:2].
3.
The data frame is then loaded into the RBR and the
Receive FIFO pointer is incremented. The error tags are
updated to reflect the status of the character data in
RBR. The data ready bit (LSR[0]) is set as soon as a
character is transferred from the shift register to the
Receive FIFO. It is reset when the Receive FIFO is
empty.
20204807
FIGURE 5. RXRDY in DMA Mode 1
7.3.2 Receive in non-FIFO Mode
Interrupt Mode
In the non-FIFO mode, FCR[0]=0, RBR can be configured to
generate an IIR Receive Data Available interrupt IIR[2] immediately after the first byte is received. Upon interrupt, the
CPU host reads the RBR and clears the interrupt. The
interrupt is reasserted when the next character is received.
(Figure 6.)
7.3.1 Receive in FIFO Mode
Interrupt Mode
In the FIFO mode, FCR[0]=1, RBR can be configured to
generate an interrupt after the FIFO pointer reaches a trigger
threshold. The interrupt causes CPU host to fetch the Rx
character in the FIFO in a burst mode and the transfer
number is set by the trigger level. The interrupt is cleared as
soon as the number of bytes in the Rx FIFO drops below the
trigger level. The Rx FIFO continues to receive new characters, and the interrupt is re-asserted when the character
reaches the trigger threshold.
To ensure the data is delivered to the host, a receive data
ready time-out interrupt IIR[3] is generated when RBR data
is not fetched by the host in 4-word length long (defined in
LCR[1:0]) plus 12 bit-time. The RBR interrupt is enabled
through IER[0]. This is equivalent of 3.6 to 4.7 frame-time.
The maximum time between a received character and a
time-out interrupt will be 147 ms at 300 baud with an 8-bit
receive word.
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28
transmission. This feature is enabled to suit specific application. The RTS flow control can be enabled by the following
steps:
• Enable auto-RTS flow control EFR[6]=1.
• The auto-RTS function is initiated by asserting RTS output pin, MCR[1]=1.
(Continued)
The auto-RTS assertion and deassertion timing is based
upon the Rx FIFO trigger level (Table 27 and Table 28).
7.3.4 Receive Flow Control Interrupt
To enable auto RTS interrupt:
• Enable auto RTS flow control EFR[6]=1.
• Enable RTS interrupt IER[6]=1.
An interrupt is generated when RTS pin makes a transition
from logic 0 to 1; IIR[5] is set to logic 1.
The receive data ready interrupt (IIR[2]) generation timing is
based upon the Rx FIFO trigger level (Table 27 and Table
28).
TABLE 27. Auto-RTS HW Flow Control on NS16C2552
20204808
FIGURE 6. Rx Non-FIFO Mode
DMA Mode
In the non-FIFO mode, the presence of a received character
in RBR causes the assertion of RXRDY at which point DMA
transfer can be initiated. Upon transfer completion RXRDY is
deasserted. DMA transfer stops and awaits for the next
character. (Figure 7.)
Rx Trigger
Level
INTR Pin
Activation
RTS
Desertion
RTS
Assertion
1
1
2
0
4
4
8
1
8
8
14
4
14
14
14
8
TABLE 28. Auto-RTS HW flow Control on NS16C2752
Rx Trigger
Level
INTR Pin
Activation
RTS
Desertion
RTS
Assertion
8
8
16
0
16
16
56
8
56
56
60
16
60
60
60
56
7.4 TRANSMIT OPERATION
Each serial channel consists of an 8-bit Transmit Shift Register (TSR) and a 16-byte (or 64-byte) Transmit FIFO. The
Transmit FIFO includes a 8-bit Transmit Holding Register
(THR). The TSR shifts data out at the 16X internal clock. A
bit time is 16 clock periods. The transmitter begins with a
start-bit followed by data bits, asserts parity-bit if enabled,
and adds the stop-bit(s). The FIFO and TSR status is reported in the LSR[6:5].
The THR is an 8-bit register providing a data interface to the
host processor. The host writes transmit data to the THR.
The THR is the Transmit FIFO input register in FIFO operation. The FIFO operation can be enabled by FCR[0]=1.
During the FIFO operation, the FIFO pointer is incremented
pointing to the next FIFO location when a data word is
written into the THR.
20204809
7.4.1 Transmit in FIFO Mode
Interrupt mode
In the NS16C2752 FIFO mode (FCR[0]=1), when the Tx
FIFO empty spaces exceed the threshold level the THR
empty flag is set (LSR[5]=1). The THR empty flag generates
FIGURE 7. RXRDY in DMA Mode 0
7.3.3 Receive Hardware Flow Control
On the line side, RTS signal provides automatic flow control
to prevent data overflow in the Receive FIFO. The RTS is
used to request remote unit to suspend or resume data
29
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NS16C2552/NS16C2752
7.0 Operation and Configuration
NS16C2552/NS16C2752
7.0 Operation and Configuration
(Continued)
a TXRDY interrupt (IIR[1]=1) when the transmit empty interrupt is enabled (IER[1]=1). Writing to THR or reading from
IIR deasserts the interrupt.
There is a two-character hysteresis in interrupt generation.
The host needs to service the interrupt by writing at least two
characters into the Tx FIFO before the next interrupt can be
generated.
The NS16C2552 does not have the FIFO threshold level
control. The interrrupt is generated when the FIFO is completely empty.
20204811
FIGURE 9. TXRDY in DMA Mode 1
7.4.2 Transmit in non-FIFO Mode
Interrupt Mode
The THR empty flag LSR[5] is set when a data word is
transferred to the TSR. THR flag can generate a transmit
empty interrupt IIR[1] enabled by IER[1]. The TSR flag
LSR[6] is set when TSR becomes empty. The host CPU may
write one character into the THR and wait for the next IIR[1]
interrupt. (Figure 10.)
20204810
FIGURE 8. Tx FIFO Mode
DMA mode
To fully take advantage of the FIFO buffer, the UART is best
operating in DMA mode 1 (FCR[3]=1) when characters are
transferred in bursts. The NS16C2752 has a Tx FIFO threshold level control in register FCR[5:4]. The threshold level
sets the number of empty spaces in the FIFO and determines when the TXRDY is asserted. If the number of empty
spaces in the FIFO exceeds the threshold, the TXRDY asserts initiating DMA transfers to fill the Tx FIFO. When the
empty spaces in the Tx FIFO becomes zero (i.e., FIFO is
full), the TXRDY deasserts and the DMA transfer stops.
TXRDY reasserts when empty space exceeds the set
threshold, starting a new DMA transfer cycle. (Figure 9.)
The NS16C2552 does not have the FIFO threshold level
control. The TXRDY is asserted when FIFO is empty and
deasserted when FIFO is full. It is equivalent of having
trigger threshold set at 16 empty spaces.
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20204812
FIGURE 10. Tx Non-FIFO Mode
DMA mode
In the DMA single transfer (mode 0), TXRDY asserts when
FIFO is empty initiating one DMA transfer and deasserts
when a character is written into the FIFO. (Figure 11.)
30
above described flow control mechanisms, flow control characters are not placed in the user accessible Rx data buffer or
FIFO.
(Continued)
During the flow control operation, when Receive FIFO
pointer reaches the upper trigger level, the UART automatically transmits Xoff1 and Xoff 2 messages via the serial TX
line output to the remote modem. When Receive FIFO
pointer position matches the lower trigger level, the UART
automatically transmits Xon1 and Xon2 characters.
Care should be taken when designing the software flow
control section of the driver. In the case where a local UART
is transmitting and the remote UART initiates flow control, an
Xoff character is sent by the remote UART.
Upon receipt the local UART ceases to transmit until such
time as the remote UART FIFO has been drained sufficiently
and it signals that it can accept further data by sending an
Xon character to the local UART.
There is a corner case in which the receipt of an Xoff by the
local UART can occur just after it has sent the last character
of a data transfer and is ready to close the transmission. If in
so doing the driver disables the local UART, it may not
receive the corresponding XON and thus can remain in a
flow-controlled state. This will persist even when the UART is
re-enabled for a succeeding transmission creating a lock-up
situation.
To resolve this lock-up issue, the driver should implement a
delay before shutting down the local transmitter at the end of
a data transfer. This delay time should be equal to the
transmission time of four characters PLUS the latency required to drain the RX FIFO on the remote side of the
connection. This will allow the remote modem to send an
Xon character and for it to be received before the local
transmitter shuts down.
20204813
FIGURE 11. TXRDY in DMA Mode 0
7.4.3 Transmit Hardware Flow Control
CTS is a flow control input used to prevent remote receiver
FIFO data overflow. The CTS input is monitored to suspend/
resume the local transmitter. The automatic CTS flow control
can be enabled to suit specific application.
• Enable auto CTS flow control EFR[7]=1.
TABLE 29. Xon/Xoff SW Flow Control on NS16C2552
7.4.4 Transmit Flow Control Interrupt
• Enable auto CTS flow control EFR[7]=1.
• Enable CTS interrupt IER[7]=1.
An interrupt is generated when CTS pin is de-asserted (logic
1). IIR[5] is set to logic 1. The transmitter suspends transmission as soon as the stop bit is shifted out. Transmission is
resumed after the CTS pin is asserted logic 0, indicating
remote receiver is ready to accept data word.
Rx Trigge
Level
INTR Pin
Activation
Xoff Char
Sent
Xon Char
Sent
1
1
1
0
4
4
4
1
8
8
8
4
14
14
14
8
TABLE 30. Xon/Xoff SW Flow Control on NS16C2752
7.5 SOFTWARE XON/XOFF FLOW CONTROL
Software flow control uses programmed Xon or Xoff characters to enable the transmit/receive flow control. The receiver
compares one or two sequentially received data words. If the
received character(s) match the programmed values, the
transmitter suspends operation as soon as the current transmitting frame is completed. When a match occurs, the Xoff (if
enabled via IER[5]) flag is set and an interrupt is generated.
Following a transmission suspension, the UART monitors
the receive data stream for an Xon character. When a match
is found, the transmission resumes and the IIR[4] flag clears.
Upon reset, the Xon/Xoff characters are cleared to logic 0.
The user may write any Xon/Xoff value desired for software
flow control. Different conditions can be set to detect Xon/
Xoff characters and suspend/resume transmissions. When
double 8-bit Xon/Xoff characters are selected, the UART
compares two consecutively received characters with two
software flow control 8-bit values (Xon1, Xon2, Xoff1, and
Xoff2) and controls transmission accordingly. Under the
Rx Trigger
Level
INTR Pin
Activation
Xoff Char
Sent
Xon Char
Sent
8
8
8
0
16
16
16
8
56
56
56
16
60
60
60
56
7.6 SPECIAL CHARACTER DETECT
UART can detect an 8-bit special character if EFR[5]=1.
When special character detect mode is enabled, the UART
compares each received character with Xoff2. If a match is
found, Xoff2 is loaded into the FIFO along with the normal
received data and IIR[4] is flagged to logic 1.
The Xon and Xoff word length is programmable between 5
and 8 bits depending on LCR[1:0] with the LSB bit mapped
to bit 0. The same word length is used for special character
comparison.
31
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NS16C2552/NS16C2752
7.0 Operation and Configuration
NS16C2552/NS16C2752
7.0 Operation and Configuration
CPU processing bandwidth. In mode 0, (FCR[3]=0), each
assertion of RXRDY and TXRDY will cause a single transfer.
Note that the user should verify the interface to make sure
the signaling is compatible with the DMA controller.
(Continued)
7.7 SLEEP MODE
With built-in transmit and receive FIFO buffers it allows data
to be transferred in blocks (mode 1) and it is ideal for more
efficient DMA operation that further saves the CPU processing bandwidth.
To reduce power consumption, NS16C2552/2752 has a per
channel sleep mode when channel is not being used. The
sleep mode requires following conditions to be met:
• Sleep mode of the respective channel is enabled
(IER[4]=1).
• No pending interrupt for the respective channel
(IIR[0]=1).
• Divisor is a non-zero value (DLL or DLM != 0x00).
• Modem inputs are not toggling (MSR[3:0]=0).
• Receiver input is idling at logic 1.
To enable the DMA mode 1, FCR[3]=1. The DMA Rx FIFO
reading is controlled by RXRDY. When FIFO data is filled to
the trigger level, RXRDY asserts and the DMA burst transfer
begins removing characters from Rx FIFO. The DMA transfer stops when Rx FIFO is empty and RXRDY deasserts.
The DMA transmit operation is controlled by TXRDY and is
different between the NS16C2552 and NS16C2752. On the
NS16C2552, the DMA operation is initiated when transmit
FIFO becomes empty and TXRDY is asserted. The DMA
controller fills the Tx FIFO and the filling stops when FIFO is
full and TXRDY is deasserted.
On the NS16C2752, the DMA transfer starts when the Tx
FIFO empty space exceeds the threshold set in FCR[5:4]
and TXRDY asserts. The transfer stops when Tx FIFO is full
and TXRDY desserts. The threshold setting gives CPU more
time to arbitrate and relinquish bus control to DMA controller
providing higher bus efficiency.
The channel wakes up from sleep mode and returns to
normal operation when one of the following conditions is
met:
• Start bit falling edge (logic 1 to 0) is detected on receiver.
• A character is loaded into the THR or Tx FIFO
• A state change on any of the modem interface inputs,
DTS, DSR, DCD, and RI.
Following the awakening, the channel can fall back into the
sleep mode when all interrupt conditions are serviced and
cleared. If channel is awakened by the modem line inputs,
reading the MSR resets the line inputs.
7.10 INFRARED MODE
NS16C2552/2752 also integrates an IrDA version 1.0 compatible infrared encoder and decoder. The infrared mode is
enabled by MCR[6]=1.
In the infrared mode, the SOUT idles at logic 0. During data
transmission, the encoder transmits a 3/16 bit wide pulse for
each logic 0. With shortened transmitter-on light pulse,
power saving is achieved.
On the receiving end, each light pulse detected translates to
a logic 0, active low (Figure 12.)
Following the awakening, the interrupts from the respective
channel has to be serviced and cleared before re-entering
into the sleep mode. The NS16C2552/2752 sleep mode can
be disabled by IER[4]=0.
7.8 INTERNAL LOOPBACK MODE
NS16C2552 incorporates internal loopback path for design
validation and diagnostic trouble shooting. In the loopback
mode, the transmitted data is looped from the transmit shift
register output to the receive shift register input internally.
The system receives its transmitted data. The loopback
mode is enabled by MCR[4]=1 (Figure 13).
In the loopback mode, Tx pin is held at logic 1 or mark
condition while RTS and DTR are de-asserted and CTS,
DRS, CD, and RI inputs are ignored. Note that Rx input must
be held at logic 1 during the loopback test. This is to prevent
false start bit detection upon exiting the loopback mode. RTS
and CTS are disabled during the test.
7.9 DMA OPERATION
LSR[6:5] provide status of the transmit FIFO and LSR[0]
provides the receive FIFO status. User may read the LSR
status bits to initiate and stop data transfers.
More efficient direct memory access (DMA) transfers can be
setup using the RXRDY and TXRDY signals. The DMA
transfers are asserted between the CPU cycles and saves
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20204814
FIGURE 12. IrDA Data Transmission
32
NS16C2552/NS16C2752
7.0 Operation and Configuration
(Continued)
20204815
FIGURE 13. Internal Loopback Functional Diagram
33
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NS16C2552/NS16C2752
In this example, L=11, so that the last bit will deviate by
8.0 Design Notes
(11 − 0.5) x ∆T = 10.5∆T(Figure 15)
8.1 DEBUGGING HINTS
Although the UART device is fairly straight forward, there are
cases that when device does not behave as expected. The
normal trouble shooting steps should include the following.
1.
Check power supply voltage and make sure it is within
the operating range.
2. Check device pin connections against the datasheet pin
list.
3.
Check an unpopulated printed circuit board (PCB)
against the schematic diagram for any shorts.
4.
Check the device clock input. For oscillator input, the
scope probe can be attached to Xin to verify the clock
voltage swing and frequency. For crystal connection,
attach the scope probe to Xout to check for the oscillation frequency.
20204817
5.
6.
Reset should be active high and normally low.
Use internal loopback mode to test the CPU host interface. If loopback mode is not working, check the CPU
interface timing including read and write bus timing.
7. If loopback mode is getting the correct data, check serial
data output and input. The transmit and receive data
may be looped back externally to verify the data path
integrity.
FIGURE 15. Deviated Baud Rate Sampling
Giving some margin for sampling error due to metastability
and jitter assuming that the bit period deviation can not be
more than 6/16 the bit time (i.e., the worst case), 0.375T. So
that
(L − 0.5) x ∆T < 0.375T
for the receiver to correctly recover the transmitted data.
Reform the equation
∆T < 0.375T / (L − 0.5)
Using the same example of 11-bit packet (L = 11), at 9600
baud, f = 9600, the sampling clock rate is f (i.e., one sample
per period) and the bit period is
T=1/f
∆T < 0.375T / (L − 0.5) = 0.375 / (f x (L − 0.5))
∆T < 0.375 / (9600 x 10.5) = 3.7 x 10-6 (sec) or 3.7 µs.
The percentage of the deviation from nominal bit period has
to be less than
8.2 CLOCK FREQUENCY ACCURACY
In the UART transmission, the transmitter clock and the
receive clock are running in two different clock domains
(unlike in some communication interface that the received
clock is a copy of the transmitter clock by sharing the same
clock or by performing clock-data-recovery). Not only the
local oscillator frequency, but also the clock divisor may
introduce error in between the transmitter and receiver’s
baud rate. The question is how much error can be tolerated
and does not cause data error?
The UART receiver has an internal sampling clock that is
16X the data rate. The sampling clock allows data to be
sampled at the 6/16 to 7/16 point of each bit. The following is
an example of a 8-bit data packet with a start, a parity, and
one stop bit. (Figure 14)
∆T / T = (0.375 / (f x (L − 0.5)) x f = 0.375 / L − 0.5)
∆T / T =3.7 x 10-6 x 9600 = 3.6%
From the above example, the error percentage increases
with longer packet length (i.e., larger L). The best case is
packet with word length 5, a start bit and a stop bit (L = 7)
that is most tolerant to error.
∆T / T = 0.375 / (L − 0.5) = 0.375 / 6.5 = 5.8%
The worst case is packet with word length 8, a start bit, a
parity bit, and two stop bits (L = 12) that is least tolerant to
error.
∆T / T = 0.375 / L − 0.5) = 0.375 / 11.5 = 3.2%
8.3 CRYSTAL REQUIREMENTS
The crystal used should meet the following requirements.
1. AT cut with parallel resonance.
2. Fundamental oscillation mode between 1 to 24 MHz.
3. Frequency tolerance and drift is well within the UART
application requirements, and they are not a concern.
20204816
FIGURE 14. Nominal Mid-bit Sampling
If a receiver baud rate generator deviates from the nominal
baud rate by ∆f, where 1/∆f = ∆T, the first sampling point will
deviate from the nominal sample point by 0.5∆T. Consequently, the second sampling point will deviate by 1.5∆T, 3rd
will deviate by 2.5∆T, and the last bit of a packet with L length
(in number of bits) will deviate by
(L − 0.5) x ∆T
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34
4.
•
•
•
•
•
•
(Continued)
The load capacitance of the crystal should match the
load capacitance of the oscillator circuitry seen by the
crystal. Under the AC conditions, the oscillator load capacitance is a lump sum of parasitic capacitance and
external capacitors. The capacitances connecting to oscillator input and output are in series seen by the crystal.
(Figure 16.) External capacitors, C1 and C2, are not
required to be very accurate. The best practice to follow
crystal manufacturer’s recommendation for the load capacitance value.
NS16C2552/NS16C2752
8.0 Design Notes
EFR 0x02.4 = 1
LCR 0x03.7:0 = 0
MCR 0x04.7 = 0
LCR 0x03.7:0 = 0xBF
EFR 0x02.4 = 0 (optional)
LCR 0x03.7:0 = temp
8.4.3 Set Xon and Xoff flow control
Set Xon1, Xoff1 to VAL1 and VAL2.
• Save LCR 0x03.7:0 in temp
• LCR 0x03.7:0 = 0xBF
• Xon1 0x04.7:0 = VAL1
• Xoff1 0x06.7:0 = VAL2
• LCR 0x03.7:0 = temp
Set Xon2, Xoff2 to VAL1 and VAL2.
• Save LCR 0x03.7:0 in temp
• LCR 0x03.7:0 = 0xBF
• Xon2 0x05.7:0 = VAL1
• Xoff2 0x07.7:0 = VAL2
• LCR 0x03.7:0 = temp
8.4.4 Set Software Flow Control
Set software flow control mode to VAL.
•
•
•
•
Save LCR 0x03.7:0 in temp
LCR 0x03.7:0 = 0xBF
EFR 0x02.3:0 = VAL
LCR 0x03.7:0 = temp
8.4.5 Configure Tx/Rx FIFO Threshold
Set Tx (2752) and Rx FIFO thresholds to VAL.
20204818
FIGURE 16. Crystal Oscillator Circuit
•
•
•
•
•
•
•
•
It should be noted that the parasitic capacitance also include
printed circuit board traces. The circuit board traces connecting to the crystal should be kept as short as possible.
8.4 CONFIGURATION EXAMPLES
8.4.1 Set Baud Rate
Set divisor values to DIV_L and DIV_M.
• LCR 0x03.7 = 1
• DLL 0x00.7:0 = DIV_L
• DLM 0x01.7:0 = DIV_M
Save LCR 0x03.7:0 in temp
LCR 0x03.7:0 = 0xBF
EFR 0x02.4 = 1
LCR 0x03.7:0 = 0
FCR 0x02.7:0 = VAL
LCR 0x03.7:0 = 0xBF
EFR 0x02.4 = 0 (optional)
LCR 0x03.7:0 = temp
8.4.6 Tx and Rx Hardware Flow Control
Configure auto RTS and CTS flow controls, enable RTS and
CTS interrupts, and assert RTS.
• LCR 0x03.7 = 0
•
•
•
•
•
•
•
•
8.4.2 Configure Prescaler Output
Set prescaler output to XIN divide by 4.
• Save LCR 0x03.7:0 in temp
• LCR 0x03.7:0 = 0xBF
• EFR 0x02.4 = 1
• LCR 0x03.7:0 = 0
• MCR 0x04.7 = 1
• LCR 0x03.7:0 = 0xBF
• EFR 0x02.4 = 0 (optional)
• LCR 0x03.7:0 = temp
Set prescaler output to XIN divide by 1.
• Save LCR 0x03.7:0 in temp
• LCR 0x03.7:0 = 0xBF
Save LCR 0x03.7:0 in temp
LCR 0x03.7:0 = 0xBF
EFR 0x02.7:6 = 2b’11
EFR 0x02.4 = 1
LCR 0x03.7:0 = 0
IER 0x01.7:6 = 2b’11
MCR 0x04.1 = 1
LCR 0x03.7:0 = temp
8.4.7 Tx and Rx DMA Control
Configure Tx and Rx in FIFO mode DMA transfers using the
threshold in FCR[7:4].
• Save LCR 0x03.7:0 in temp
• LCR 0x03.7:0 = 0
• FCR 0x02.0 = 1
35
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NS16C2552/NS16C2752
8.0 Design Notes
8.5 DIFFERENCES BETWEEN THE PC16552D AND
NS16C2552/2752
The following are differences between the versions of UART
that helps user to identify the feature differences.
(Continued)
• FCR 0x02.3 = 1
• LCR 0x03.7:0 = temp
TABLE 31. Differences among the UART products
Features
PC16552D
NS16C2552
16-byte
16-byte
64-byte
4.5V to 5.5V
2.97V to 5.5V
2.97V to 5.5V
5.0Mbps
Tx and Rx FIFO sizes
Supply voltage
Highest baud rate
NS16C2752
1.5Mbps
5.0Mbps
Highest clock input frequency
24MHz
80MHz
80MHz
Operating temperature
0 - 70˚C
-40 to 85˚C
-40 to 85˚C
Enhanced Register Set
No
Yes
Yes
Sleep mode IER[4]
No
Yes
Yes
Xon, Xoff, and Xon-Any software auto flow control
No
Yes
Yes
CTS and RTS hardware auto flow control
No
Yes
Yes
Interrupt source ID in IIR
3-bit
5-bit
5-bit
1 level
1 level
4 levels
IrDA v1.0 mode MCR[6]
No
Yes
Yes
Clock divisor 1 or 4 select MCR[7]
No
Yes
Yes
Tx FIFO trigger level select FCR[5:4]
8.6 NOTES ON TX FIFO OF NS16C2752
host writes to the THR or reads from IIR.
3. When the number of empty spaces reaches the threshold level, an interrupt is generated. If the host reads the
IIR but does not fill the Tx FIFO, the INTR is deasserted.
However, if the host still does not fill the Tx FIFO, the
FIFO becomes empty. The THR empty interrupt is not
generated because the host has not written to the Tx
FIFO and the interrupt service is not complete.
4. When the number of empty spaces reaches the threshold level, a THR empty interrupt is generated. If the host
writes at least one character into the Tx FIFO, the interrupt is serviced and the THR empty flag is deasserted.
Subsequently, if the host fails to fill the FIFO before it
reaches empty, a THR empty interrupt will be asserted.
5. Reset Tx FIFO causes a THR empty interrupt.
Notes on interrupt assertion and deassertion.
1. To avoid frequent interrupt request generation, there is a
hysteresis of two characters. When the transmit FIFO
threshold is enabled and the number of empty spaces
reaches the threshold, a THR empty interrupt is generated requesting the CPU to fill the transmit FIFO. The
host has to fill at least two characters in the Tx FIFO
before another THR empty interrupt can be generated.
The DMA request TXRDY works differently. When the
number of empty spaces exceeds the threshold, TXRDY
asserts initiating the DMA transfer. The TXRDY deasserts when the transmit FIFO is full.
2.
When the number of empty spaces reaches the threshold level, an interrupt is generated. If the host does not
fill the FIFO, the interrupt will remain asserted until the
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ESD Rating HBM, 1.5K and 100 pF
1)
ESD Rating Machine Model
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
10.0 DC and AC Specifications
Operating Temperature
−65˚C to +150˚C
All Input or Output Voltages with
respect to Vss
Power Dissipation
400V
Note: Typical specifications are at TA=25˚C, and represent
most likely parametric norms at the time of product characterization. The typical specifications are not guaranteed.
−40˚C to +85˚C
Storage Temperature
10.1 DC SPECIFICATIONS
−0.5V to +6.5V
TA = -40˚C to +85˚C, VCC = +2.97V to 5.5V, VSS = 0V, unless
otherwise specified.
250mW
3.3V, 10%
Symbol
Parameter
8kV
Conditions
5.0V, 10%
Min
Max
Min
Max
Units
VILX
Clock Input Low Voltage
-0.3
0.6
-0.5
0.6
V
VIHX
Clock Input High Voltage
2.4
5.5
3.1
5.5
V
VIL
Input Low Voltage
-0.3
0.8
-0.5
0.8
V
VIH
Input High Voltage
2.0
5.5
2.2
5.5
V
VOL
Output Low Voltage
0.4
V
IOL = 6mA
IOL = 4mA
VOH
Output High Voltage
0.4
IOH = -6mA
2.4
IOH = -1mA
IIL
Input Low Leakage
IIH
Input High Leakage
IDD
Current Consumption
V
V
2.0
V
10
Static clock input
10
µA
10
10
µA
1.6
3.0
mA
10.2 CAPACITANCE
TA = 25˚C, VDD = VSS = 0V
Symbol
CXIN
CXOUT
CIN
COUT
CI/O
Parameter
Conditions
Min
Typ
Max
Units
Clock Input Capacitance
7
pF
Clock Output Capacitance
7
pF
Input Capacitance
Output Capacitance
fc = 1 MHz
Unmeasured Pins Returned
to VSS
Input/Output Capacitance
5
pF
6
pF
10
pF
10.3 AC SPECIFICATIONS
TA = -40˚C to +85˚C, VCC = +2.97V to 5.5V, VSS = 0V, unless
otherwise specified.
Symbol
Parameter
Condition
3.3V Limits
Min
fc
Crystal Frequency
tHILO
External Clock Low/High
fOSC
External Clock Frequency
tRST
Reset Pulse Width
n
BCLK
Max
5.0V Limits
Min
24
6
70
Baud Rate Divisor
1
Baud Clock
24
MHz
80
MHz
6
80
ns
70
16
2 -1
1
Units
Max
ns
16
2 -1
16 x of data rate
1/16 of a bit duration
Host Interface
tAR
Address Setup Time
10
10
ns
tRA
Address Hold Time
1
1
ns
tRD
RD Strobe Width
35
24
ns
tDY
Read Cycle Delay
35
tRDV
Data Access Time
24
35
37
ns
24
ns
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NS16C2552/NS16C2752
9.0 Absolute Maximum Ratings (Note
NS16C2552/NS16C2752
10.0 DC and AC Specifications
Symbol
Parameter
(Continued)
Condition
3.3V Limits
5.0V Limits
Min
Max
18
Units
Min
Max
0
18
tHZ
Data Disable Time
0
tWR
WR Strobe Width
35
tDY
Write Cycle Delay
35
24
ns
tDS
Data Setup Time
12
12
ns
tDH
Data Hold Time
4
4
ns
24
ns
ns
Modem Control
tMDO
Delay from WR to Output
20
15
ns
tSIM
Delay from Modem input to
Interrupt output
20
15
ns
tRIM
Delay to Reset interrupt from
RD falling edge
23
17
ns
tSINT
Delay from Stop to Interrupt
Set
4
4
Bclk
tRINT
Delay from of RD to Reset
Interrupt
45
30
ns
tSTI
Delay from center of Start to
INTR Set
16
10
ns
tWST
Delay from WR to Transmit
Start
16
Bclk
tHR
Delay from WR to interrupt
clear
34
22
ns
Line Receive and Transmit
(Note 2)
0
16
0
DMA Interface
tWXI
Delay from WR to TXRDY
rising edge
27
18
ns
tSXA
Delay from Center of Start to
TXRDY falling edge
8
8
Bclk
tSSR
Delay from Stop to RXRDY
falling edge
4
4
Bclk
tRXI
Delay from /RD to RXRDY
rising edge
27
18
ns
Note 1: Maximum ratings indicate limits beyond which permanent damage may occur. Continuous operation at these limits is not intended and should be limited
to those conditions specified under DC electrical characteristics.
Note 2: The BCLK period decreases with increasing reference clock input. At higher clock input frequency, the number of BCLK increases.
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NS16C2552/NS16C2752
11.0 Timing Diagrams
20204819
FIGURE 17. External Clock Input
20204820
FIGURE 18. Modem Control Timing
20204821
FIGURE 19. Host Interface Read Timing
39
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NS16C2552/NS16C2752
11.0 Timing Diagrams
(Continued)
20204822
FIGURE 20. Host Interface Write Timing
20204823
FIGURE 21. Receiver Timing
20204824
FIGURE 22. Receiver Timing Non-FIFO Mode
20204825
FIGURE 23. Receiver Timing FIFO Mode
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NS16C2552/NS16C2752
11.0 Timing Diagrams
(Continued)
20204826
FIGURE 24. Transmitter Timing
20204827
FIGURE 25. Transmitter Timing Non-FIFO Mode
20204828
FIGURE 26. Transmitter Timing FIFO Mode
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NS16C2552/NS16C2752
12.0 Physical Dimensions
inches (millimeters) unless otherwise noted
44–PLCC Package
Order Number NS16C2552TVA, NS16C2752TVA
NS Package Number V44A
48–TQFP Package
Order Number NS16C2552TVS, NS16C2752TVS
NS Package Number VBC48A
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42
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the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances
and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at:
www.national.com/quality/green.
Lead free products are RoHS compliant.
National Semiconductor
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Fax: 81-3-5639-7507
Email: [email protected]
Tel: 81-3-5639-7560
NS16C2552/NS16C2752 Dual UART with 16-byte/64-byte FIFO’s and up to 5 Mbit/s Data Rate
Notes