Data Sheet

INTEGRATED CIRCUITS
SCC68692
Dual asynchronous receiver/transmitter
(DUART)
Product data
Supersedes data of 1998 Sep 04
2004 Mar 03
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
• Parity, framing, and overrun error detection
• False start bit detection
• Line break detection and generation
• Programmable channel mode
DESCRIPTION
The Philips Semiconductors SCC68692 Dual Universal
Asynchronous Receiver/Transmitter (DUART) is compatible with
SCN68681. It is a single-chip CMOS-LSI communications device
that provides two full-duplex asynchronous receiver/transmitter
channels in a single package. It is compatible with other S68000
family devices and can also interface easily with other
microprocessors. The DUART can be used in a polled or interrupt
driven systems.
– Normal (full-duplex)
– Automatic echo
– Local loopback
The operating mode and data format of each channel can be
programmed independently. Additionally, each receiver and
transmitter can select its operating speed as one of eighteen fixed
baud rates, a 16X clock derived from a programmable counter/timer,
or an external 1X or 16X clock. The baud rate generator and
counter/timer can operate directly from a crystal or from external
clock inputs. The ability to independently program the operating
speed of the receiver and transmitter make the DUART particularly
attractive for dual-speed channel applications such as clustered
terminal systems.
– Remote loopback
– Multidrop mode (also called ‘wake-up’ or ‘9-bit’)
• Multi-function 6-bit input port
– Can serve as clock or control inputs
– Change of state detection on four inputs
– Inputs have typically >100 kΩ pull-up resistors
• Multi-function 8-bit output port
– Individual bit set/reset capability
– Outputs can be programmed to be status/interrupt signals
Each receiver is quadruple buffered to minimize the potential of
receiver over-run or to reduce interrupt overhead in interrupt driven
systems. In addition, a flow control capability is provided to disable a
remote DUART transmitter when the receiver buffer is full.
• Versatile interrupt system
– Single interrupt output with eight maskable interrupting
conditions
Also provided on the SCC68692 are a multipurpose 6-bit input port
and a multipurpose 8-bit output port. These can be used as general
purpose I/O ports or can be assigned specific functions (such as
clock inputs or status/interrupt outputs) under program control.
– Interrupt vector output on interrupt acknowledge
– Output port can be configured to provide a total of up to six
separate wire-ORable interrupt outputs
• Maximum data transfer rates: 1X – 1 MB/sec, 16X – 125 kB/sec
• Automatic wake-up mode for multidrop applications
• Start-end break interrupt/status
• Detects break which originates in the middle of a character
• On-chip crystal oscillator
• Power down mode
• Receiver timeout mode
• Commercial and Industrial temperature range versions
• TTL compatible
• Single +5 V power supply
FEATURES
• S68000 bus compatible
• Dual full-duplex asynchronous receiver/transmitters
• Quadruple buffered receiver data register
• Programmable data format:
– 5 to 8 data bits plus parity
– Odd, even, no parity or force parity
– 1, 1.5 or 2 stop bits programmable in 1/16-bit increments
• 16-bit programmable Counter/Timer
• Programmable baud rate for each receiver and transmitter
selectable from:
– 22 fixed rates: 50 to 115.2 k baud
– Non-standard rates to 115.2 kb
– Non-standard user-defined rate derived from programmable
counter/timer
– External 1X or 16X clock
ORDERING INFORMATION
COMMERCIAL
INDUSTRIAL
VCC = +5 V ± 10 %,
Tamb = 0 to +70 °C
VCC = +5 V ± 10 %,
Tamb = –40 to +85 °C
DWG #
40-Pin (600 mils wide) Plastic Dual In-Line Package (DIP)
SCC68692C1N40
SCC68692E1N40
SOT129-1
44-Pin Plastic Leaded Chip Carrier (PLCC)
SCC68692C1A44
SCC68692E1A44
SOT187-2
DESCRIPTION
2004 Mar 03
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Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
PIN CONFIGURATIONS
INDEX
CORNER
A1
1
40 VCC
IP3
2
39 IP4
A2
3
38 IP5
IP1
4
37 IACKN
A3
5
36 IP2
A4
6
35 CSN
6
40
1
7
39
PLCC
IP0
7
34 RESETN
R/WN
8
33 X2
DTACKN 9
RxDB 10
18
PIN/FUNCTION
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
31 RxDA
TxDB 11
30 TxDA
OP1 12
29 OP0
OP3 13
28 OP2
OP5 14
27 OP4
OP7 15
26 OP6
D1 16
25 D0
D3 17
24 D2
D5 18
23 D4
D7 19
22 D6
GND 20
28
TOP VIEW
32 X1/CLK
DIP
29
17
21 INTRN
PIN/FUNCTION
NC
A1
IP3
A2
IP1
A3
A4
IP0
R/WN
DTACKN
RxDB
NC
TxDB
OP1
OP3
OP5
OP7
D1
D3
D5
D7
GND
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
NC
INTRN
D6
D4
D2
D0
OP6
OP4
OP2
OP0
TxDA
NC
RxDA
X1/CLK
X2
RESETN
CSN
IP2
IACKN
IP5
IP4
VCC
SD00144
Figure 1. Pin Configurations
ABSOLUTE MAXIMUM RATINGS1
SYMBOL
Tamb2
Tstg
VCC3
VS
3
PD
PARAMETER
RATING
UNIT
Note 4
°C
Storage temperature range
–65 to +150
°C
Voltage from VCC to GND
–0.5 to +7.0
V
Operating ambient temperature range
–0.5 to VCC +0.5
V
Package power dissipation
Voltage from any pin to GND
DIP40
2.97
W
Package power dissipation
PLCC44
2.66
W
Derating factor above 25 °C
DIP40
24
mW/°C
Derating factor above 25 °C
PLCC44
21
mW/°C
NOTES:
1. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or any other condition above those indicated in the operation section of this specification is not implied.
2. For operating at elevated temperatures, the device must be derated.
3. This product includes circuitry specifically designed for the protection of its internal devices from damaging effects of excessive static
charge. Nonetheless, it is suggested that conventional precautions be taken to avoid applying any voltages larger than the rated maxima.
4. Parameters are valid over specified temperature range.
2004 Mar 03
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Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
BLOCK DIAGRAM
8
D0–D7
CHANNEL A
BUS BUFFER
TRANSMIT
HOLDING REG
TxDA
TRANSMIT
SHIFT REGISTER
OPERATION CONTROL
R/WN
DTACKN
CSN
A1–A4
RESETN
RECEIVE
HOLDING REG (3)
ADDRESS
DECODE
RxDA
4
RECEIVE
SHIFT REGISTER
R/W CONTROL
MRA1, 2
CRA
SRA
INTERRUPT CONTROL
INTRN
IMR
IACKN
TxDB
CHANNEL B
(AS ABOVE)
ISR
RxDB
INTERNAL DATABUS
BAUD RATE
GENERATOR
TIMING
TIMING
CONTROL
IVR
INPUT PORT
CHANGE OF
STATE
DETECTORS (4)
6
IP0-IP5
IPCR
ACR
CLOCK
SELECTORS
COUNTER/
TIMER
OUTPUT PORT
FUNCTION
SELECT LOGIC
X1/CLK
XTAL OSC
8
OP0-OP7
OPCR
X2
OPR
CSRA
CSRB
ACR
CTUR
CTLR
VCC
GND
SD00145
Figure 2. Block Diagram
2004 Mar 03
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Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
PIN DESCRIPTION
SYMBOL
D0–D7
CSN
R/WN
PIN NO.
TYPE
25,16,24,17
I/O
23,18,22,19
35
I
NAME AND FUNCTION
Data Bus: Bidirectional 3-State data bus used to transfer commands, data and status between the DUART
and the CPU. D0 is the least significant bit.
Chip Enable: Active-LOW input signal. When LOW, data transfers between the CPU and the DUART are
enabled on D0–D7 as controlled by the R/WN and A1–A4 inputs. When CEN is HIGH, the DUART places
the D0–D7 lines in the 3-State condition.
8
I
A1–A4
RESETN
1,2,5,6
34
I
I
DTACKN
9
O
INTRN
21
O
IACKN
37
I
X1/CLK
32
I
X2
33
I
RxDA
RxDB
TxDA
31
10
30
I
I
O
TxDB
11
O
Channel B Transmitter Serial Data Output: The least significant bit is transmitted first. This output is held
in the ‘mark’ condition when the transmitter is disabled, idle, or when operating in local loopback mode.
‘Mark’ is HIGH, ‘space’ is LOW.
OP0
29
O
OP1
12
O
OP2
28
O
OP3
13
O
OP4
OP5
OP6
OP7
IP0
27
14
26
15
7
O
O
O
O
I
IP1
4
I
IP2
36
I
Output 0: General purpose output or Channel A request to send (RTSAN, active-LOW). Can be
deactivated automatically on receive or transmit.
Output 1: General purpose output or Channel B request to send (RTSBN, active-LOW). Can be
deactivated automatically on receive or transmit.
Output 2: General purpose output, or Channel A transmitter 1X or 16X clock output, or Channel A receiver
1X clock output.
Output 3: General purpose output or open-drain, active-LOW counter/timer output or Channel B transmitter
1X clock output, or Channel B receiver 1X clock output.
Output 4: General purpose output or Channel A open-drain, active-LOW, RxRDYAN/FFULLAN output.
Output 5: General purpose output or Channel B open-drain, active-LOW, RxRDYBN/FFULLBN output.
Output 6: General purpose output or Channel A open-drain, active-LOW, TxRDYAN output.
Output 7: General purpose output or Channel B open-drain, active-LOW, TxRDYBN output.
Input 0: General purpose input or Channel A clear to send active-LOW input (CTSAN). Pin has an internal
VCC pull-up device supplying 1 to 4 µA of current.
Input 1: General purpose input or Channel B clear to send active-LOW input (CTSBN). Pin has an internal
VCC pull-up device supplying 1 to 4 µA of current.
Input 2: General purpose input or Channel B receiver external clock input (RxCB), or counter/timer external
clock input. When external clock is used by the receiver, the received data is sampled on the rising edge of
the clock. Pin has an internal VCC pull-up device supplying 1 to 4 µA of current.
IP3
2
I
Input 3: General purpose input or Channel A transmitter external clock input (TxCA). When the external
clock is used by the transmitter, the transmitted data is clocked on the falling edge of the clock. Pin has an
internal VCC pull-up device supplying 1 to 4 µA of current.
IP4
39
I
Input 4: General purpose input or Channel A receiver external clock input (RxCA). When the external clock
is used by the receiver, the received data is sampled on the rising edge of the clock. Pin has an internal
VCC pull-up device supplying 1 to 4 µA of current.
IP5
38
I
Input 5: General purpose input or Channel B transmitter external clock input (TxCB). When the external
clock is used by the transmitter, the transmitted data is clocked on the falling edge of the clock. Pin has an
internal VCC pull-up device supplying 1 to 4 µA of current.
VCC
GND
40
20
I
I
Power Supply: +5 V supply input.
Ground
2004 Mar 03
Read/Write: A HIGH input indicates a read cycle and a LOW input indicates a write cycle, when a cycle is
initiated by assertion of the CSN input.
Address Inputs: Select the DUART internal registers and ports for read/write operations.
Reset: A LOW level clears internal registers (SRA, SRB, IMR, ISR, OPR, OPCR), initializes the IVR to hex
0F, puts OP0–OP7 in the HIGH state, stops the counter/timer, and puts Channels A and B in the inactive
state, with the TxDA and TxDB outputs in the mark (HIGH) state. Resets Test Mode, sets MR pointer to MR1.
Data Transfer Acknowledge: 3-State active-LOW output asserted in write, read, or interrupt cycles to
indicate proper transfer of data between the CPU and the DUART.
Interrupt Request: Active-LOW, open-drain output which signals the CPU that one or more of the eight
maskable interrupting conditions are true.
Interrupt Acknowledge: Active-LOW input indicating an interrupt acknowledge cycle. In response, the
DUART will place the interrupt vector on the data bus and will assert DTACKN if it has an interrupt pending.
Crystal 1: Crystal connection or an external clock input. A crystal of a clock the appropriate frequency
(nominally 3.6864 MHz) must be supplied at all times. For crystal connections see Figure 9, Clock Timing.
Crystal 2: Crystal connection. See Figure 9. If a crystal is not used it is best to keep this pin not connected
although it is permissible to ground it.
Channel A Receiver Serial Data Input: The least significant bit is received first. “Mark” is HIGH, “space” is LOW.
Channel B Receive Serial Data Input: The least significant bit is received first. “Mark” is HIGH, “space” is LOW.
Channel A Transmitter Serial Data Output: The least significant bit is transmitted first. This output is held
in the “mark” condition when the transmitter is disabled, idle or when operating in local loopback mode.
“Mark” is HIGH, “space” is LOW.
5
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
DC ELECTRICAL CHARACTERISTICS1, 2, 3
SYMBOL
PARAMETER
TEST CONDITIONS
LIMITS
UNIT
Min
Typ
Max
–
2.0
2.5
0.8VCC
–
–
–
–
0.8
–
–
–
V
V
V
V
IOH = –400 µA
–
VCC – 0.5
–
–
0.4
–
V
V
VIN = 0 V to VCC
VIN = 0 V
VIN = VCC
–10
–75
0
–
–
–
+10
0
75
µA
µA
µA
VOUT = VCC, X1 = 0
VOUT = 0 V, X1 = 0
VOUT = 0 V, X1 = VCC
VOUT = VCC, X1 = VCC
0
–10
–75
1
–
–
–
–
+75
–1
0
10
µA
mA
µA
mA
VIN = 0 V to VCC
VIN = 0 V to VCC
–10
–20
–
–
+10
+10
µA
µA
VIL
VIH6
VIH7
VIH
Input LOW voltage
Input HIGH voltage (except X1/CLK)
Input HIGH voltage (except X1/CLK)
Input HIGH voltage (X1/CLK)
VOL
VOH4
Output LOW voltage
Output HIGH voltage (except OD outputs)
IIX1PD
IILX1
IIHX1
X1/CLK input current – power-down
X1/CLK input LOW current – operating
X1/CLK input HIGH current – operating
IOHX2
IOHX2S
IOLX2
IOLX2S
X2 output HIGH current – operating
X2 output HIGH short circuit current – operating
X2 output LOW current – operating
X2 output LOW short circuit current – operating
and power-down
II
Input leakage current:
All except input port pins
Input port pins
IOZH
IOZL
Output off current HIGH, 3-State data bus
Output off current LOW, 3-State data bus
VIN = VCC
VIN = 0 V
–
–10
–
–
10
–
µA
µA
IODL
IODH
Open-drain output LOW current in off State
Open-drain output HIGH current in off State
VIN = 0 V
VIN = VCC
–10
–
–
–
10
–
µA
µA
TTL input levels
CMOS input levels
TTL input levels
CMOS input levels
–
–
–
–
–
–
–
–
10
10
3.0
2.0
mA
mA
mA
mA
IOL = 2.4 mA
Power supply current5
Operating mode
ICC
Power down mode8
NOTES:
1. Parameters are valid over specified temperature range.
2. All voltage measurements are referenced to ground (GND). For testing, all inputs swing between 0.4 V and 2.4 V with a transition time of
5 ns maximum. For X1/CLK this swing is between 0.4 V and 4.4 V. All time measurements are referenced at input voltages of 0.8 V and
2.0 V and output voltages of 0.8 V and 2.0 V, as appropriate.
3. Typical values are at +25 °C, typical supply voltages, and typical processing parameters.
4. Test conditions for outputs: CL = 150 pF, except interrupt outputs. Test condition for interrupt outputs: CL = 50 pF, RL = 2.7 kΩ to VCC.
5. All outputs are disconnected. Inputs are switching between TTL levels of 2.4 V and 0.4 V or CMOS levels of VCC – 0.2 V and VSS + 0.2 V.
6. Tamb ≥ 0 °C
7. Tamb < 0 °C
8. See UART application note for power-down currents less than 5 µA.
2004 Mar 03
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Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
AC CHARACTERISTICS1, 2, 4
SYMBOL
FIGURE
PARAMETER
LIMITS
UNIT
Min
Typ3
Max
RESET pulse width
200
–
–
ns
A1–A4 set-up time to CSN LOW
A1–A4 hold time from CSN LOW
RWN set-up time to CSN HIGH
RWN holdup time to CSN HIGH
CSN HIGH pulse width
CSN or IACKN HIGH from DTACKN LOW
Data valid from CSN or IACKN LOW
RDN LOW to data bus active
Data bus floating from CSN or IACKN HIGH
RDN HIGH to data bus invalid
Data set-up time to CLK HIGH
Data hold time from CSN HIGH
DTACKN LOW from read data valid
DTACKN LOW (read cycle) from CLK HIGH
DTACKN LOW (write cycle) form CLK HIGH
DTACKN HIGH from CSN or IACKN HIGH
DTACKN high-impedance from CSN or IACKN HIGH
CSN or IACKN set-up time to clock HIGH
10
100
0
0
160
20
–
15
–
20
100
0
0
–
–
–
–
90
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
175
–
125
–
–
–
–
125
125
100
125
–
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Reset Timing
tRES
1
Bus Timing5
tAS
tAH
tRWS
tRWH
tCSW8
tCSD9
tDD
tDA8
tDF8
tDI8
tDS
tDH
tDAL
tDCR
tDCW
tDAH
IDAT
tCSC7
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
4
4,5,6
4
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
4,5,6
Port Timing5
tPS
tPH
tPD
7
7
7
Port input set-up time to CSN LOW
Port input hold time from CSN HIGH
Port output valid from CSN HIGH
0
0
–
–
–
–
–
–
400
ns
ns
ns
6
INTRN (or OP3–OP7 when used as interrupts) negated from:
Read RHR (RxRDY/FFULL interrupt)
Write THR (TxRDY interrupt)
Reset command (break interrupt)
Stop C/T command (counter interrupt)
Read IPCR (input port change interrupt)
Write IMR (clear of interrupt mask bit)
–
–
–
–
–
–
–
–
–
–
–
–
300
300
300
300
300
300
ns
ns
ns
ns
ns
ns
100
0
100
100
220
100
100
220
0
0
–
3.6864
–
–
–
–
–
–
–
–
–
4
–
4
–
2
1
–
2
1
ns
MHz
ns
MHz
ns
MHz
MHz
ns
MHz
MHz
–
–
–
–
350
150
ns
ns
Interrupt Timing
tIR10
Clock Timing
tCLK
fCLK11
tCTC
fCTC9
tRX
7
7
7
7
7
fRX9
7
tTX
7
fTX
9
7
X1/CLK HIGH or LOW time
X1/CLK frequency
CTCLK (IP2) HIGH or LOW time
CTCLK (IP2) frequency
RxC HIGH or LOW time
RxC frequency (16X)
(1X)
TxC HIGH or LOW time
TxC frequency (16X)
(1X)
Transmitter Timing
tTXD
tTCS
8
8
TxD output delay from TxC external clock input on IP pin
Output delay from TxC LOW at OP pin to TxD data output
Receiver Timing
tRXS
9
RxD data set-up time before RxC HIGH at external clock input on IP pin
240
–
–
ns
tRXH
9
RxD data hold time after RxC HIGH at external clock input on IP pin
200
–
–
ns
NOTES:
1. Parameters are valid over specified temperature range.
2. All voltage measurements are referenced to ground (GND). For testing, all inputs swing between 0.4 V and 2.4 V with a transition time of
5 ns maximum. For X1/CLK this swing is between 0.4 V and 4.4 V. All time measurements are referenced at input voltages of 0.8 V and
2.0 V and output voltages of 0.8 V and 2.0 V, as appropriate.
2004 Mar 03
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Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
3. Typical values are at +25 °C, typical supply voltages, and typical processing parameters.
4. Test conditions for outputs: CL = 150 pF, except interrupt outputs. Test condition for interrupt outputs: CL = 50 pF, RL = 2.7 kΩ to VCC.
5. This specification will impose maximum 68000 CPU CLK to 6 MHz. Higher CPU CLK can be used if repeating bus reads are not performed.
Consecutive write operations to the same command register require at least three edges of the X1 clock between writes.
6. This specification imposes a lower bound on CSN and IACKN LOW, guaranteeing that it will be LOW for at least 1 CLK period. This requirement is made on CSN only to insure assertion of DTACKN and not to guarantee operation of the part.
7. This specification is made only to insure that DTACKN is asserted with respect to the rising edge of the X1/CLK pin as shown in the timing
diagram, not to guarantee operation of the part. If the set-up time is violated, DTACKN may be asserted as shown, or may be asserted one
clock cycle later.
8. Guaranteed by characterization of sample units.
9. Minimum frequencies are not tested but are guaranteed by design.
10. 325 ns maximum for Tamb > 70 °C.
11. Operation to 0 MHz is assured by design. Minimum test frequency is 2.0 MHz.
12. See UART application note for power-down currents less than 5 µA.
If an external is used instead of a crystal, X1 should be driven using
a configuration similar to the one in Figure 9.
BLOCK DIAGRAM
The SCC68692 DUART consists of the following eight major
sections: data bus buffer, operation control, interrupt control, timing,
communications Channels A and B, input port and output port. Refer
to the Block Diagram (Figure 2).
BRG
The baud rate generator operates from the oscillator or external
clock input and is capable of generating 18 commonly used data
communications baud rates ranging from 50 to 38.4 K baud. A
3.6864 MHz crystal or external clock must be used to get the
standard baud rate. The clock outputs from the BRG are at 16X the
actual baud rate. The counter/timer can be used as a timer to
produce a 16X clock for any other baud rate by counting down the
crystal clock or an external clock. The four clock selectors allow the
independent selection, for each receiver and transmitter, of any of
these baud rates or external timing signal.
Data Bus Buffer
The data bus buffer provides the interface between the external and
internal data buses. It is controlled by the operation control block to
allow read and write operations to take place between the controlling
CPU and the DUART.
Operation Control
The operation control logic receives operation commands from the
CPU and generates appropriate signals to internal sections to
control device operation. It contains address decoding and read and
write circuits to permit communications with the microprocessor via
the data bus buffer. The DTACKN output is asserted during write
and read cycles to indicate to the CPU that data has been latched
on a write cycle, or that valid data is present on the bus on a read
cycle.
Counter/Timer (C/T)
The counter timer is a 16-bit programmable divider that operates
one of three modes: Counter, Timer or Time Out mode. In all three
modes it uses the 16-bit value loaded to the CTUR and CTLR
registers. (Counter timer upper and lower preset registers).
• In the Timer mode it generates a square wave.
• In the Counter mode it generates a time delay.
• In the Time Out mode it monitors the receiver data flow and
Interrupt Control
A single active-LOW interrupt output (INTRN) is provided which is
activated upon the occurrence of any of eight internal events.
Associated with the interrupt system are the Interrupt Mask Register
(IMR) and the Interrupt Status Register (ISR), the Auxiliary Control
Register (ACR), and the Interrupt Vector Register (IVR). The IMR
may be programmed to select only certain conditions to cause
INTRN to be asserted. The ISR can be read by the CPU to
determine all currently active interrupting conditions. When IACKN is
asserted, and the DUART has an interrupt pending, the DUART
responds by placing the contents of the IVR register on the data bus
and asserting DTACKN.
signals data flow has paused. In the Time Out mode the receiver
controls the starting/stopping of the C/T.
The counter operates as a down counter and sets its output bit in
the ISR (Interrupt Status Register) each time it passes through ‘0’.
The output of the counter/timer may be seen on one of the OP pins
or as an Rx or Tx clock.
The Timer/Counter is controlled with six (6) “commands”; Start C/T,
Stop C/T, write C/T, preset registers, read C/T value, set or reset
time out mode.
Outputs OP3–OP7 can be programmed to provide discrete interrupt
outputs for the transmitter, receivers, and counter/timer.
Please see the detail of the commands under the Counter/Timer
register descriptions.
Communications Channels A and B
TIMING CIRCUITS
Each communications channel of the SCC68692 comprises a
full-duplex asynchronous receiver/transmitter (UART). The operating
frequency for each receiver and transmitter can be selected
independently from the baud rate generator, the counter timer, or
from an external input.
Crystal Clock
The timing block consists of a crystal oscillator, a baud rate
generator, a programmable 16-bit counter/timer, and four clock
selectors. The crystal oscillator operates directly from a crystal
connected across the X1/CLK and X2 inputs. If an external clock of
the appropriate frequency is available, it may be connected to
X1/CLK. The clock serves as the basic timing reference for the Baud
Rate Generator (BRG), the counter/timer, and other internal circuits.
A clock signal within the limits specified in the specifications section
of this data sheet must always be supplied to the DUART.
2004 Mar 03
The transmitter accepts parallel data from the CPU, converts it to a
serial bit stream, inserts the appropriate start, stop, and optional
parity bits and outputs a composite serial stream of data on the TxD
output pin. The receiver accepts serial data on the RxD pin,
converts this serial input to parallel format, checks for start bit, stop
bit, parity bit (if any), or break condition and sends an assembled
character to the CPU.
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Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
is provided. Characters cannot be loaded into the THR while the
transmitter is disabled.
Input Port
The inputs to this unlatched 6-bit port can be read by the CPU by
performing a read operation at address H’D’. A HIGH input results in
a logic 1 while a LOW input results in a logic 0. D7 will always be
read as a logic 1 and D6 will reflect the level of IP2. The pins of this
port can also serve as auxiliary inputs to certain portions of the
DUART logic.
The transmitter converts the parallel data from the CPU to a serial
bit stream on the TxD output pin. It automatically sends a start bit
followed by the programmed number of data bits, an optional parity
bit, and the programmed number of stop bits. The least significant
bit is sent first. Following the transmission of the stop bits, if a new
character is not available in the THR, the TxD output remains HIGH
and the TxEMT bit in the Status Register (SR) will be set to ‘1’.
Transmission resumes and the TxEMT bit is cleared when the CPU
loads a new character into the THR. If the transmitter is disabled, it
continues operating until the character currently being transmitted is
completely sent out. The transmitter can be forced to send a
continuous LOW condition by issuing a send break command.
Four change-of-state detectors are provided which are associated
with inputs IP3, IP2, IP1 and IP0. A HIGH-to-LOW or LOW-to-HIGH
transition of these inputs, lasting longer than 25 – 50 µs, will set the
corresponding bit in the input port change register. The bits are
cleared when the register is read by the CPU. Any change-of-state
can also be programmed to generate an interrupt to the CPU.
The input port pulse detection circuitry uses a 38.4 kHz sampling
clock derived from one of the baud rate generator taps. This results
in a sampling period of slightly more than 25 µs (this assumes that
the clock input is 3.6864 MHz). The detection circuitry, in order to
guarantee that a true change in level has occurred, requires two
successive samples at the new logic level be observed. As a
consequence, the minimum duration of the signal change is 25 µs if
the transition occurs “coincident with the first sample pulse”. The
50 µs time refers to the situation in which the change-of-state is “just
missed” and the first change-of-state is not detected until 25 µs later.
All the IP pins have a small pull-up device that will source 1 to 4 µA
of current from VCC. These pins do not require pull-up devices or
VCC connections if they are not used.
The transmitter can be reset through a software command. If it is
reset, operation ceases immediately and the transmitter must be
enabled through the command register before resuming operation. If
CTS operation is enable, the CTSN input must be LOW in order for
the character to be transmitted. If it goes HIGH in the middle of a
transmission, the character in the shift register is transmitted and
TxDA then remains in the marking state until CTSN goes LOW. The
transmitter can also control the deactivation of the RTSN output. If
programmed, the RTSN output will be reset one bit time after the
character in the transmit shift register and transmit holding register
(if any) are completely transmitted, if the transmitter has been
disabled.
Output Port
Receiver
The output port pins may be controlled by the OPR, OPCR, MR and
the CR registers. Via appropriate programming they may be just
another parallel port to external circuits, or they may represent many
internal conditions of the UART. When this 8-bit port is used as a
general purpose output port, the output port pins assume a state
which is the complement of the Output Port Register (OPR).
OPR(n) = 1 results in OP(n) = LOW and vice versa. Bits of the OPR
can be individually set and reset. A bit is set by performing a write
operation at address H’E’ with the accompanying data specifying the
bits to be reset (1 = set, 0 = no change). Likewise, a bit is reset by a
write at address H’F’ with the accompanying data specifying the bits
to be reset (1 = reset, 0 = no change).
The SCC68692 is conditioned to receive data when enabled through
the command register. The receiver looks for a HIGH-to-LOW
(mark-to-space) transition of the start bit on the RxD input pin. If a
transition is detected, the state of the RxD pin is sampled each 16X
clock for 7-1/2 clocks (16X clock mode) or at the next rising edge of
the bit time clock (1X clock mode). If RxD is sampled HIGH, the start
bit is invalid and the search for a valid start bit begins again. If RxD
is still LOW, a valid start bit is assumed and the receiver continues
to sample the input at one bit time intervals at the theoretical center
of the bit, until the proper number of data bits and parity bit (if any)
have been assembled, and one stop bit has been detected. The
least significant bit is received first. The data is then transferred to
the Receive Holding Register (RHR) and the RxRDY bit in the SR is
set to a ‘1’. This condition can be programmed to generate an
interrupt at OP4 or OP5 and INTRN. If the character length is less
than 8 bits, the most significant unused bits in the RHR are set to
zero.
Outputs can be also be individually assigned specific functions by
appropriate programming of the Channel A mode registers (MR1A,
MR2A), the Channel B mode registers (MR1B, MR2B), and the
Output Port Configuration Register (OPCR).
Output ports are driven HIGH on hardware reset. Please note that
these pins drive both HIGH and LOW. However when they are
programmed to represent interrupt type functions (such as receiver
ready, transmitter ready or counter/timer ready) they will be switched
to an open drain configuration in which case an external pull-up
device would be required.
After the stop bit is detected, the receiver will immediately look for
the next start bit. However, if a non-zero character was received
without a stop bit (framing error) and RxD remains LOW for one half
of the bit period after the stop bit was sampled, then the receiver
operates as if a new start bit transition had been detected at that
point (one-half bit time after the stop bit was sampled).
OPERATION
Transmitter
The parity error, framing error, and overrun error (if any) are strobed
into the SR at the received character boundary, before the RxRDY
status bit is set. If a break condition is detected (RxD is LOW for the
entire character including the stop bit), a character consisting of all
zeros will be loaded into the RHR and the received break bit in the
SR is set to ‘1’. The RxD input must return to HIGH for two (2) clock
edges of the X1 crystal clock for the receiver to recognize the end of
the break condition and begin the search for a start bit. This will
usually require a HIGH time of one X1 clock period or 3 X1
edges since the clock of the controller is not synchronous to
the X1 clock.
The SCC68692 is conditioned to transmit data when the transmitter
is enabled through the command register. The SCC68692 indicates
to the CPU that it is ready to accept a character by setting the
TxRDY bit in the status register. This condition can be programmed
to generate an interrupt request at OP6 or OP7 and INTRN. When a
character is loaded into the Transmit Holding Register (THR), the
above conditions are negated. Data is transferred from the holding
register to transmit shift register when it is idle or has completed
transmission of the previous character. The TxRDY conditions are
then asserted again which means one full character time of buffering
2004 Mar 03
SCC68692
9
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
programmed to interrupt the CPU when the receive FIFO is full, and
the message ends before the FIFO is full, the CPU may not know
there is data left in the FIFO. The CTU and CTL value would be
programmed for just over one character time, so that the CPU would
be interrupted as soon as it has stopped receiving continuous data.
This mode can also be used to indicate when the serial line has
been marking for longer than the programmed time limit. In this
case, the CPU has read all of the characters from the FIFO, but the
last character received has started the count. If there is no new data
during the programmed time interval, the counter ready bit will get
set, and an interrupt can be generated.
Receiver FIFO
The RHR consists of a First-In-First-Out (FIFO) stack with a
capacity of three characters. Data is loaded from the receive shift
register into the topmost empty position of the FIFO. The RxRDY bit
in the status register is set whenever one or more characters are
available to be read, and a FFULL status bit is set if all three stack
positions are filled with data. Either of these bits can be selected to
cause an interrupt. A read of the RHR outputs the data at the top of
the FIFO. After the read cycle, the data FIFO and its associated
status bits (see below) are ‘popped’ thus emptying a FIFO position
for new data.
This mode is enabled by writing the appropriate command to the
command register. Writing an ‘Ax’ to CRA or CRB will invoke the
timeout mode for that channel. Writing a ‘Cx’ to CRA or CRB will
disable the timeout mode. The timeout mode should only be used by
one channel at once, since it uses the C/T. CTU and CTL must be
loaded with a value greater than the normal receive character
period. The timeout mode disables the regular START/STOP
Counter commands and puts the C/T into counter mode under the
control of the received data stream. Each time a received character
is transferred from the shift register to the RHR, the C/T is stopped
after 1 C/T clock, reloaded with the value in CTU and CTL and then
restarted on the next C/T clock. If the C/T is allowed to end the
count before a new character has been received, the counter ready
bit, ISR[3], will be set. If IMR[3] is set, this will generate an interrupt.
Since receiving a character after the C/T has timed out will clear the
counter ready bit, ISR[3], and the interrupt. Invoking the ‘Set
Timeout Mode On’ command, CRx = ‘Ax’, will also clear the counter
ready bit and stop the counter until the next character is received.
Receiver Status Bits
In addition to the data word, three status bits (parity error, framing
error, and received break) are also appended to each data character
in the FIFO (overrun is not). Status can be provided in two ways, as
programmed by the error mode control bit in the mode register. In
the ‘character’ mode, status is provided on a character-by-character
basis; the status applies only to the character at the top of the FIFO.
In the ‘block’ mode, the status provided in the SR for these three bits
is the logical-OR of the status for all characters coming to the top of
the FIFO since the last ‘reset error’ command was issued. In either
mode reading the SR does not affect the FIFO. The FIFO is
‘popped’ only when the RHR is read. Therefore the status register
should be read prior to reading the FIFO.
If the FIFO is full when a new character is received, that character is
held in the receive shift register until a FIFO position is available. If
an additional character is received while this state exits, the
contents of the FIFO are not affected; the character previously in the
shift register is lost and the overrun error status bit (SR[4] will be
set-upon receipt of the start bit of the new (overrunning) character.
This mode is reset by the “Disable Time-out Mode” command
(CR x’C0) must be used.
The receiver can control the deactivation of RTS. If programmed to
operate in this mode, the RTSN output will be negated when a valid
start bit was received and the FIFO is full. When a FIFO position
becomes available, the RTSN output will be re-asserted
automatically. This feature can be used to prevent an overrun, in the
receiver, by connecting the RTSN output to the CTSN input of the
transmitting device.
Time Out Mode Caution
When operating in the special time out mode, it is possible to
generate what appears to be a “false interrupt”, i.e., an interrupt
without a cause. This may result when a time-out interrupt occurs
and then, before the interrupt is serviced, another character is
received, i.e., the data stream has started again. (The interrupt
latency is longer than the pause in the data strea.) In this case,
when a new character has been receiver, the counter/timer will be
restarted by the receiver, thereby withdrawing its interrupt. If, at this
time, the interrupt service begins for the previously seen interrupt, a
read of the ISR will show the “Counter Ready” bit not set. If nothing
else is interrupting, this read of the ISR will return a x’00 character.
Receiver Reset and Disable
Receiver disable stops the receiver immediately – data being
assembled if the receiver shift register is lost. Data and status in the
FIFO is preserved and may be read. A re-enable of the receiver
after a disable will cause the receiver to begin assembling
characters at the next start bit detected. A receiver reset will discard
the present shift register data, reset the receiver ready bit (RxRDY),
clear the status of the byte at the top of the FIFO and re-align the
FIFO read/write pointers. This has the appearance of “clearing or
flushing” the receiver FIFO. In fact, the FIFO is NEVER cleared! The
data in the FIFO remains valid until overwritten by another received
character. Because of this, erroneous reading or extra reads of the
receiver FIFO will mis-align the FIFO pointers and result in the
reading of previously read data. A receiver reset will re-align the
pointers.
Multidrop Mode
The DUART is equipped with a wake up mode for multidrop
applications. This mode is selected by programming bits MR1A[4:3]
or MR1B[4:3] to ‘11’ for Channels A and B, respectively. In this mode
of operation, a ‘master’ station transmits an address character
followed by data characters for the addressed ‘slave’ station. The
slave stations, with receivers that are normally disabled, examine
the received data stream and ‘wake up’ the CPU (by setting RxRDY)
only upon receipt of an address character. The CPU compares the
received address to its station address and enables the receiver if it
wishes to receive the subsequent data characters. Upon receipt of
another address character, the CPU may disable the receiver to
initiate the process again.
Timeout Mode
The timeout mode uses the received data stream to control the
counter. Each time a received character is transferred from the shift
register to the RHR, the counter is restarted. If a new character is
not received before the counter reaches zero count, the counter
ready bit is set, and an interrupt can be generated. This mode can
be used to indicate when data has been left in the Rx FIFO for more
than the programmed time limit. Otherwise, if the receiver has been
2004 Mar 03
SCC68692
A transmitted character consists of a start bit, the programmed
number of data bits, and Address/Data (A/D) bit, and the
programmed number of stop bits. The polarity of the transmitted A/D
bit is selected by the CPU by programming bit MR1A[2]/MR1B[2].
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Product data
Dual asynchronous receiver/transmitter (DUART)
The contents of certain control registers are initialized to zero on
RESET. Care should be exercised if the contents of a register are
changed during operation, since certain changes may cause
operational problems. For example, changing the number of bits per
character while the transmitter is active may cause the transmission
of an incorrect character. In general, the contents of the MR, the
CSR, and the OPCR should only be changed while the receiver(s)
and transmitter(s) are not enabled, and certain changes to the ACR
should only be made while the C/T is stopped.
MR1A[2]/MR1B[2] = 0 transmits a zero in the A/D bit position, which
identifies the corresponding data bits as data while
MR1A[2]/MR1B[2] = 1 transmits a one in the A/D bit position, which
identifies the corresponding data bits as an address. The CPU
should program the mode register prior to loading the corresponding
data bits into the THR.
In this mode, the receiver continuously looks at the received data
stream, whether it is enabled or disabled. If disabled, it sets the
RxRDY status bit and loads the character into the RHR FIFO if the
received A/D bit is a one (address tag), but discards the received
character if the received A/D bit is a zero (data tag). If enabled, all
received characters are transferred to the CPU via the RHR. In
either case, the data bits are loaded into the data FIFO while the
A/D bit is loaded into the status FIFO position normally used for
parity error (SRA[5] or SRB[5]). Framing error, overrun error, and
break detect operate normally whether or not the receive is enabled.
Mode registers 1 and 2 of each channel are accessed via
independent auxiliary pointers. The pointer is set to MR1x by
RESET or by issuing a ‘reset pointer’ command via the
corresponding command register. Any read or write of the mode
register while the pointer is at MR1x, switches the pointer to MR2x.
The pointer then remains at MR2x, so that subsequent accesses are
always to MR2x unless the pointer is reset to MR1x as described
above.
PROGRAMMING
Mode, command, clock select, and status registers are duplicated
for each channel to provide total independent operation and control.
Refer to Table 2 for register bit descriptions. The reserved registers
at addresses H‘02’ and H‘0A’ should never be read during normal
operation since they are reserved for internal diagnostics.
The operation of the DUART is programmed by writing control words
into the appropriate registers. Operational feedback is provided via
status registers which can be read by the CPU. The addressing of
the registers is described in Table 1.
Table 1.
A3
SCC68692
Register Addressing
A2
A1
A0
READ (RDN = 0)
WRITE (WRN = 0)
0
0
0
0
Mode Register A (MR1A, MR2A)
Mode Register A (MR1A, MR2A)
0
0
0
1
Status Register A (SRA)
Clock Select Register A (CSRA)
0
0
1
0
BRG Test
Command Register A (CRA)
0
0
1
1
Rx Holding Register A (RHRA)
Tx Holding Register A (THRA)
0
1
0
0
Input Port Change Register (IPCR)
Aux. Control Register (ACR)
0
1
0
1
Interrupt Status Register (ISR)
Interrupt Mask Register (IMR)
0
1
1
0
Counter/Timer Upper Value (CTU)
C/T Upper Preset Value (CRUR)
0
1
1
1
Counter/Timer Lower Value (CTL)
C/T Lower Preset Value (CTLR)
1
0
0
0
Mode Register B (MR1B, MR2B)
Mode Register B (MR1B, MR2B)
1
0
0
1
Status Register B (SRB)
Clock Select Register B (CSRB)
1
0
1
0
1X/16X Test
Command Register B (CRB)
1
0
1
1
Rx Holding Register B (RHRB)
Tx Holding Register B (THRB)
1
1
0
0
Interrupt Vector Register (IVR)
Interrupt Vector Register (IVR)
1
1
0
1
Input Ports IP0 to IP6
Output Port Conf. Register (OPCR)
1
1
1
0
Start Counter Command
Set Output Port Bits Command
1
1
1
1
Stop Counter Command
Reset Output Port Bits Command
* See Table 6 for BRG Test frequencies in this data sheet, and “Extended baud rates for SCN2681, SCN68681, SCC2691, SCC2692,
SCC68681 and SCC2698B” in application notes elsewhere in this publication
MR1A[6] – Channel A Receiver Interrupt Select
This bit selects either the Channel A receiver ready status (RxRDY)
or the Channel A FIFO full status (FFULL) to be used for CPU
interrupts. It also causes the selected bit to be output on OP4 if it is
programmed as an interrupt output via the OPCR.
MR1A – Channel A Mode Register 1
MR1A is accessed when the Channel A MR pointer points to MR1.
The pointer is set to MR1 by RESET or by a ‘set pointer’ command
applied via CRA. After reading or writing MR1A, the pointer will point
to MR2A.
MR1A[5] – Channel A Error Mode Select
This bit selects the operating mode of the three FIFOed status bits
(FE, PE, received break) for Channel A. In the ‘character’ mode,
status is provided on a character-by-character basis; the status
applies only to the character at the top of the FIFO. In the ‘block’
mode, the status provided in the SR for these bits is the
accumulation (logical-OR) of the status for all characters coming to
the top of the FIFO since the last ‘reset error’ command for Channel
A was issued.
MR1A[7] – Channel A Receiver Request-to-Send Control
This bit controls the deactivation of the RTSAN output (OP0) by the
receiver. This output is normally asserted by setting OPR[0] and
negated by resetting OPR[0]. MR1A[7] = 1 causes RTSAN to be
negated upon receipt of a valid start bit if the Channel A FIFO is full.
However, OPR[0] is not reset and RTSAN will be asserted again
when an empty FIFO position is available. This feature can be used
for flow control to prevent overrun in the receiver by using the
RTSAN output signal to control the CTSN input of the transmitting
device.
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Product data
Dual asynchronous receiver/transmitter (DUART)
3. Received data is not sent to the local CPU, and the error status
conditions are inactive.
4. The received parity is not checked and is not regenerated for
transmission, i.e., transmitted parity is as received.
5. The receiver must be enabled.
6. Character framing is not checked, and the stop bits are retransmitted as received.
7. A received break is echoed as received until the next valid start
bit is detected.
MR1A[4:3| – Channel A Parity Mode Select
If ‘with parity’ or ‘force parity’ is selected a parity bit is added to the
transmitted character and the receiver performs a parity check on
incoming data MR1A[4:3] = 11 selects Channel A to operate in the
special multidrop mode described in the Operation section.
MR1A[2] – Channel A Parity Type Select
This bit selects the parity type (odd or even) if the ‘with parity’ mode
is programmed by MR1A[4:3], and the polarity of the forced parity bit
if the ‘force parity’ mode is programmed. It has no effect if the ‘no
parity’ mode is programmed. In the special multidrop mode it selects
the polarity of the A/D bit.
The user must exercise care when switching into and out of the
various modes. The selected mode will be activated immediately
upon mode selection, even if this occurs in the middle of a received
or transmitted character. Likewise, if a mode is deselected the
device will switch out of the mode immediately. An exception to this
is switching out of autoecho or remote loopback modes: if the
de-selection occurs just after the receiver has sampled the stop bit
(indicated in autoecho by assertion of RxRDY), and the transmitter
is enabled, the transmitter will remain in autoecho mode until the
entire stop has been retransmitted.
MR1A[1:0] – Channel A Bits Per Character Select
This field selects the number of data bits per character to be
transmitted and received. The character length does not include the
start, parity, and stop bits.
MR2A – Channel A Mode Register 2
MR2A is accessed when the Channel A MR pointer points to MR2,
which occurs after any access to MR1A. Accesses to MR2A do not
change the pointer.
MR2A[5] – Channel A Transmitter Request-to-Send Control
CAUTION: When the transmitter controls the OP pin (usually used
for the RTSN signal) the meaning of the pin is not RTSN at all!
Rather, it signals that the transmitter has finished the transmission
(i.e., end of block).
MR2A[7:6] – Channel A Mode Select
Each channel of the DUART can operate in one of four modes.
MR2A[7:6] = 00 is the normal mode, with the transmitter and
receiver operating independently. MR2A[7:6] = 01 places the
channel in the automatic echo mode, which automatically
re-transmits the received data. The following conditions are true
while in automatic echo mode:
1. Received data is re-clocked and retransmitted on the TxDA output.
2. The receive clock is used for the transmitter.
3. The receiver must be enabled, but the transmitter need not be
enabled.
4. The Channel A TxRDY and TxEMT status bits are inactive.
5. The received parity is checked, but is not regenerated for transmission, i.e. transmitted parity bit is as received.
6. Character framing is checked, but the stop bits are retransmitted
as received.
7. A received break is echoed as received until the next valid start
bit is detected.
8. CPU to receiver communication continues normally, but the CPU
to transmitter link is disabled.
This bit allows deactivation of the RTSN output by the transmitter.
This output is manually asserted and negated by the appropriate
commands issued via the command register. MR2[5] set to ‘1’
caused the RTSN to be reset automatically one bit time after the
character(s) in the transmit shift register and in the THR (if any) are
completely transmitted (including the programmed number of stop
bits) if a previously issued transmitter disable is pending. This
feature can be used to automatically terminate the transmission as
follows:
1. Program the auto-reset mode: MR2[5] = 1
2. Enable transmitter, if not already enabled
3. Assert RTSN via command
4. Send message
5. After the last character of the message is loaded to the THR,
disable the transmitter. (If the transmitter is underrun, a special
case exists. See note below.)
6. The last character will be transmitted and the RTSN will be reset
one bit time after the last stop bit is sent.
Two diagnostic modes can also be configured. MR2A[7:6] = 10
selects local loopback mode. In this mode:
1. The transmitter output is internally connected to the receiver
input.
2. The transmit clock is used for the receiver.
3. The TxDA output is held HIGH.
4. The RxDA input is ignored.
5. The transmitter must be enabled, but the receiver need not be
enabled.
6. CPU to transmitter and receiver communications continue normally.
NOTE: The transmitter is in an underrun condition when both the
TxRDY and the TxEMT bits are set. This condition also exists
immediately after the transmitter is enabled from the disabled or
reset state. When using the above procedure with the transmitter in
the underrun condition, the issuing of the transmitter disable must be
delayed from the loading of a single, or last, character until the
TxRDY becomes active again after the character is loaded.
MR2A[4] – Channel A Clear-to-Send Control
If this bit is ‘0’, CTSAN has no effect on the transmitter. If this bit is a
‘1’, the transmitter checks the state of CTSAN (IPO) each time it is
ready to send a character. If IPO is asserted (LOW), the character is
transmitted. If it is negated (HIGH), the TxDA output remains in the
marking state and the transmission is delayed until CTSAN goes
LOW. Changes in CTSAN while a character is being transmitted do
not affect the transmission of that character.
The second diagnostic mode is the remote loopback mode, selected
by MR2A[7:6] = 11. In this mode:
1. Received data is re-clocked and retransmitted on the TxDA output.
2. The receive clock is used for the transmitter.
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Product data
Dual asynchronous receiver/transmitter (DUART)
Table 2.
SCC68692
Register Bit Formats
MR1A
MR1B
BIT 7
RxRTS
CONTROL
BIT 6
RxINT
SELECT
BIT 5
ERROR
MODE*
0 = No
1 = Yes
0 = RxRDY
1 = FFULL
0 = Char
1 = Block
BIT 4
BIT 3
BIT 2
PARITY
TYPE
PARITY MODE
00 = With Parity
01 = Force Parity
10 = No Parity
11 = Multidrop Mode
BIT 1
BIT 0
BITS PER
CHARACTER
00 = 5
01 = 6
10 = 7
11 = 8
0 = Even
1 = Odd
NOTE:
*In block error mode, block error conditions must be cleared by using the error reset command (command 4x) or a receiver reset.
BIT 7
BIT 6
CHANNEL MODE
MR2A
MR2B
BIT 5
TxRTS
CONTROL
BIT 4
CTS
ENABLE Tx
0 = No
1 = Yes
0 = No
1 = Yes
00 = Normal
01 = Auto-Echo
10 = Local loop
11 = Remote loop
BIT 3
BIT 2
BIT 1
BIT 0
STOP BIT LENGTH*
0 = 0.563
1 = 0.625
2 = 0.688
3 = 0.750
4 = 0.813
5 = 0.875
6 = 0.938
7 = 1.000
8 = 1.563
9 = 1.625
A = 1.688
B = 1.750
C = 1.813
D = 1.875
E = 1.938
F = 2.000
NOTE: *Add 0.5 to values shown for 0 – 7 if channel is programmed for 5 bits/char.
BIT 7
BIT 6
BIT 5
RECEIVER CLOCK SELECT
See Text
CSRA
CSRB
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
TRANSMITTER CLOCK SELECT
See Text
* See Table 6 for BRG Test frequencies in this data sheet, and “Extended baud rates for SCN2681, SCN68681, SCC2691, SCC2692,
SCC68681 and SCC2698B” in application notes elsewhere in this publication
BIT 7
CRA
CRB
BIT 3
BIT 2
BIT 1
BIT 0
MISCELLANEOUS COMMANDS
BIT 6
BIT 5
BIT 4
DISABLE Tx
ENABLE Tx
DISABLE Rx
ENABLE Rx
See Text
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
NOTE: Access to the miscellaneous commands should be separated by 3 X1 clock edges. A disabled transmitter cannot be loaded.
SRA
SRB
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
RECEIVED
BREAK*
FRAMING
ERROR*
PARITY
ERROR*
OVERRUN
ERROR
TxEMT
TxRDY
FFULL
RxRDY
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
NOTE: *These status bits are appended to the corresponding data character in the receive FIFO. A read of the status provides these bits
(7:5) from the top of the FIFO together with bits (4:0). These bits are cleared by a “reset error status” command. In character mode they are
discarded when the corresponding data character is read from the FIFO. In block error mode, block error conditions must be cleared by using
the error reset command (command 4x) or a receiver reset.
OPCR
OPR
OPR bit
BIT 7
BIT 6
BIT 5
BIT 4
OP7
OP6
OP5
OP4
0 = OPR[7]
1 = TxRDYB
0 = OPR[6]
1 = TxRDYA
0 = OPR[5]
1 = RxRDY/
FFULLB
0 = OPR[4]
1 = RxRDY/
FFULLA
BIT 7
0
BIT 6
1
0
BIT 5
1
0
1
0
ACR
2004 Mar 03
BIT 6
BIT 5
BRG SET
SELECT
COUNTER/TIMER
MODE AND SOURCE
0 = set 1
1 = set 2
See Table 4
BIT 2
BIT 1
OP3
BIT 3
BIT 0
OP2
00 = OPR[3]
01 = C/T OUTPUT
10 = TxCB(1x)
11 = RxCB(1x)
BIT 4
OP pin
1
0
1
0
1
0
1
NOTE:
The level at the OP pin is the inverse of the bit in the OPR register.
BIT 7
BIT 3
00 = OPR[2]
01 = TxCA(16x)
10 = TxCA(1x)
11 = RxCA(1x)
BIT 2
BIT 1
BIT 0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
BIT 4
13
BIT 3
BIT 2
BIT 1
BIT 0
DELTA
IP3 INT
DELTA
IP2 INT
DELTA
IP1 INT
DELTA
IP0 INT
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
Table 2.
IPCR
ISR
IMR
SCC68692
Register Bit Formats (Continued)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DELTA
IP3
DELTA
IP2
DELTA
IP1
DELTA
IP0
IP3
IP2
IP1
IP0
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = LOW
1 = HIGH
0 = LOW
1 = HIGH
0 = LOW
1 = HIGH
0 = LOW
1 = HIGH
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
IN PORT
CHANGE
DELTA
BREAK B
RxRDY/
FFULLB
TxRDYB
COUNTER
READY
DELTA
BREAK A
RxRDY/
FFULLA
TxRDYA
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
0 = No
1 = Yes
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
IN PORT
CHANGE
INT
DELTA
BREAK B
INT
RxRDY/
FFULLB
INT
TxRDYB
INT
COUNTER
READY
INT
DELTA
BREAK A
INT
RxRDY/
FFULLA
INT
TxRDYA
INT
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
0 = Off
1 = On
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
C/T[15]
C/T[14]
C/T[13]
C/T[12]
C/T[11]
C/T[10]
C/T[9]
C/T[8]
CTUR
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
C/T[7]
C/T[6]
C/T[5]
C/T[4]
C/T[3]
C/T[2]
C/T[1]
C/T[0]
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
IVR[7]
IVR[6]
IVR[5]
IVR[4]
IVR[3]
IVR[2]
IVR[1]
IVR[0]
CTLR
IVR
The bit definitions for mode register are identical to the bit definitions
for MR2A, except that all control actions apply to the Channel B
receiver and transmitter and the corresponding inputs and outputs.
MR2A[3:0] – Channel A Stop Bit Length Select
This field programs the length of the stop bit appended to the
transmitted character. Stop bit lengths of 9/16 to 1 and 1–9/16 to
2 bits, in increments of 1/16 bit, can be programmed for character
lengths of 6, 7, and 8 bits. For a character lengths of 5 bits, 1–1/16
to 2 stop bits can be programmed in increments of 1/16 bit. In all
cases, the receiver only checks for a ‘mark’ condition at the center
of the first stop bit position (one bit time after the last data bit, or
after the parity bit is enabled).
Table 3.
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
If an external 1X clock is used for the transmitter, MR2A[3] = 0
selects one stop bit and MR2A[3] = 1 selects two stop bits to be
transmitted.
MR1B – Channel B Mode Register 1
MR1B is accessed when the Channel B MR pointer points to MR1.
The pointer is set to MR1 by RESET or by a ‘set pointer’ command
applied via CRB. After reading or writing MR1B, the pointer will point
to MR2B.
The bit definitions for this register are identical to MR1A, except that
all control actions apply to the Channel B receiver and transmitter
and the corresponding inputs and outputs.
MR2B – Channel B Mode Register 2
MR2B is accessed when the Channel B MR pointer points to MR2,
which occurs after any access to MR1B. Accesses to MR2B do not
change the pointer.
2004 Mar 03
Baud Rate
CSRA[7:4]
ACR[7] = 0
50
110
134.5
200
300
600
1,200
1,050
2,400
4,800
7,200
9,600
38.4k
Timer
IP4–16X
IP4–1X
Baud Rate ACR[7] = 1
75
110
134.5
150
300
600
1,200
2,000
2,400
4,800
1,800
9,600
19.2k
Timer
IP4–16X
IP4–1X
NOTE: The receiver clock is always a 16X clock except for CSRA[7:4] = 1111.
14
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
CSRA – Channel A Clock Select Register
0110
Start break. Forces the TxDA output LOW (spacing). If the transmitter is empty the
start of the break condition will be delayed up to two bit times. If the transmitter is active the break begins when transmission of the character is completed. If a character
is in the THR, the start of the break will be delayed until that character, or any other
loaded subsequently are transmitted. The transmitter must be enabled for this command to be accepted.
0111
Stop break. The TxDA line will go HIGH (marking) within two bit times. TxDA will remain HIGH for one bit time before the next character, if any, is transmitted.
1000
Assert RTSN. Causes the RTSN output to be asserted (LOW).
1001
Negate RTSN. Causes the RTSN output to be negated (HIGH).
1010
Set Timeout Mode On. The receiver in this channel will restart the C/T as each receive character is transferred from the shift register to the RHR. The C/T is placed
in the counter mode, the START/STOP counter commands are disabled, the counter
is stopped, and the Counter Ready Bit, ISR[3], is reset.
CSRA[7:4] – Channel A Receiver Clock Select
This field selects the baud rate clock for the Channel A transmitter.
The field definition is shown in Table 3.
CSRA[3:0] – Channel A Transmitter Clock Select
This field selects the baud rate clock for the Channel A transmitter.
The field definition is as shown in Table 3, except as follows:
CSRA[3:0]
ACR[7] = 0
Baud Rate ACR[7] = 1
1110
1111
IP3–16X
IP3–1X
IP3–16X
IP3–1X
The transmitter clock is always a 16X clock except for
CSRA[3:0] = 1111.
1011
Not used.
1100
Disable Timeout Mode. This command returns control of the C/T to the regular
START/STOP counter commands. It does not stop the counter, or clear any pending
interrupts. After disabling the timeout mode, a ‘Stop Counter’ command should be
issued
1101
Not used.
1110
Power Down Mode On. In this mode, the DUART oscillator is stopped and all functions requiring this clock are suspended. The execution of commands other than disable power down mode (1111) requires a X1/CLK. While in the power down mode,
do not issue any commands to the CR except the disable power down mode command. It is recommended that the transmitter and receiver be disabled prior to placing the DUART into power down mode. This command is in CRA only. Design Note:
The part will not output DTACKN while in power down mode. Use automatic DTACKN
generation.
1111
Disable Power Down Mode. This command restarts the oscillator. After invoking this
command, wait for the oscillator to start up before writing further commands to the
CR. This command is in CRA only.
CSRB – Channel B Clock Select Register
CSRB[7:4] – Channel B Receiver Clock Select
This field selects the baud rate clock for the Channel B receiver. The
field definition is as shown in Table 3, except as follows:
CSRB[7:4]
ACR[7] = 0
1110
1111
IP2–16X
IP2–1X
Baud Rate ACR[7] = 1
IP2–16X
IP2–1X
The receiver clock is always a 16X clock except for
CSRB[7:4] = 1111.
CRA[3] – Disable Channel A Transmitter
This command terminates transmitter operation and reset the
TxDRY and TxEMT status bits. However, if a character is being
transmitted or if a character is in the THR when the transmitter is
disabled, the transmission of the character(s) is completed before
assuming the inactive state.
CSRB[3:0] – Channel B Transmitter Clock Select
This field selects the baud rate clock for the Channel B transmitter.
The field definition is as shown in Table 3, except as follows:
CSRB[3:0]
ACR[7] = 0
Baud Rate ACR[7] = 1
1110
1111
IP5–16X
IP5–1X
IP5–16X
IP5–1X
CRA[2] – Enable Channel A Transmitter
Enables operation of the Channel A transmitter. The TxRDY status
bit will be asserted.
The transmitter clock is always a 16X clock except for
CSRB[3:0] = 1111.
CRA[1] – Disable Channel A Receiver
This command terminates operation of the receiver immediately – a
character being received will be lost. The command has no effect on
the receiver status bits or any other control registers. If the special
multidrop mode is programmed, the receiver operates even if it is
disabled. See Operation section.
CRA – Channel A Command Register
CRA is a register used to supply commands to Channel A. Multiple
commands can be specified in a single write to CRA as long as the
commands are non-conflicting, e.g., the ‘enable transmitter’ and
‘reset transmitter’ commands cannot be specified in a single
command word.
NOTE: Access to the upper four bits of the command register
should be separated by three (3) edges of the X1 clock.
CRA[0] – Enable Channel A Receiver
Enables operation of the Channel A receiver. If not in the special
wake up mode, this also forces the receiver into the search for start
bit state.
CRA[7:4] – Miscellaneous Commands
The encoded value of this field may be used to specify a single
command as follows:
0000
No command.
0001
Reset MR pointer. Causes the Channel A MR pointer to point to MR1.
0010
Reset receiver. Resets the Channel A receiver as if a hardware reset had been applied. The receiver is disabled and the FIFO is flushed.
0011
Reset transmitter. Resets the Channel A transmitter as if a hardware reset had been
applied.
0100
Reset error status. Clears the Channel A Received Break, Parity Error, and Overrun
Error bits in the status register (SRA[7:4]). Used in character mode to clear OE status
(although RB, PE and FE bits will also be cleared) and in block mode to clear all error
status after a block of data has been received.
0101
Reset Channel A break change interrupt. Causes the Channel A break detect
change bit in the interrupt status register (ISR[2]) to be cleared to zero.
2004 Mar 03
SCC68692
CRB – Channel B Command Register
CRB is a register used to supply commands to Channel B. Multiple
commands can be specified in a single write to CRB as long as the
commands are non-conflicting, e.g., the ‘enable transmitter’ and
‘reset transmitter’ commands cannot be specified in a single
command word.
The bit definitions for this register are identical to the bit definitions
for CRA, with the exception of commands “Ex” and “Fx” which are
used for power down mode. These two commands are not used in
CRB. All other control actions that apply to CRA also apply to CRB.
15
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
receive shift register because the FIFO is full, FFULL will not be
reset when the CPU reads the RHR.
SRA – Channel A Status Register
SRA[7] – Channel A Received Break
This bit indicates that an all zero character of the programmed
length has been received without a stop bit. Only a single FIFO
position is occupied when a break is received: further entries to the
FIFO are inhibited until the RxDA line to the marking state for at
least one-half a bit time two successive edges of the internal or
external 1X clock. This will usually require a HIGH time of one X1
clock period or 3 X1 edges since the clock of the controller is
not synchronous to the X1 clock.
SRA[0] – Channel A Receiver Ready (RxRDYA)
This bit indicates that a character has been received and is waiting
in the FIFO to be read by the CPU. It is set when the character is
transferred from the receive shift to the FIFO and reset when the
CPU reads the RHR, if after this read there are not more characters
still in the FIFO.
SRB – Channel B Status Register
The bit definitions for this register are identical to the bit definitions
for SRA, except that all status applies to the Channel B receiver and
transmitter and the corresponding inputs and outputs.
When this bit is set, the Channel A ‘change in break’ bit in the ISR
(ISR[2]) is set. ISR[2] is also set when the end of the break
condition, as defined above, is detected.
OPCR – Output Port Configuration Register
The break detect circuitry can detect breaks that originate in the
middle of a received character. However, if a break begins in the
middle of a character, it must persist until at least the end of the next
character time in order for it to be detected.
OPCR[7] – OP7 Output Select
This bit programs the OP7 output to provide one of the following:
0 The complement of OPR[7].
1 The Channel B transmitter interrupt output which is the
complement of TxRDYB. When in this mode OP7 acts as an
open-drain output. Note that this output is not masked by the
contents of the IMR.
SRA[6] – Channel A Framing Error
This bit, when set, indicates that a stop bit was not detected when
the corresponding data character in the FIFO was received. The
stop bit check is made in the middle of the first stop bit position.
OPCR[6] – OP6 Output Select
This bit programs the OP6 output to provide one of the following:
0 The complement of OPR[6].
1 The Channel A transmitter interrupt output which is the
complement of TxRDYA. When in this mode OP6 acts as an
open-drain output. Note that this output is not masked by the
contents of the IMR.
SRA[5] – Channel A Parity Error
This bit is set when the ‘with parity’ or ‘force parity’ mode is
programmed and the corresponding character in the FIFO was
received with incorrect parity. In the special multidrop mode, the
parity error bit stores the received A/D bit.
SRA[4] – Channel A Overrun Error
This bit, when set, indicates that one or more characters in the
received data stream have been lost. It is set upon receipt of a new
character when the FIFO is full and a character is already in the
receive shift register waiting for an empty FIFO position. When this
occurs, the character in the receive shift register (and its break
detect, parity error and framing error status, if any) is lost. This bit is
cleared by a ‘reset error status’ command.
OPCR[5] – OP5 Output Select
This bit programs the OP5 output to provide one of the following:
0 The complement of OPR[5].
1 The Channel B transmitter interrupt output which is the
complement of ISR[5]. When in this mode OP5 acts as an
open-drain output. Note that this output is not masked by the
contents of the IMR.
SRA[3] – Channel A Transmitter Empty (TxEMTA)
This bit will be set when the transmitter underruns, i.e., both the
TxEMT and TxRDY bits are set. This bit and TxRDY are set when
the transmitter is first enabled and at any time it is re-enabled after
either (a) reset, or (b) the transmitter has assumed the disabled
state. It is always set after transmission of the last stop bit of a
character if no character is in the THR awaiting transmission.
OPCR[4] – OP4 Output Select
This field programs the OP4 output to provide one of the following:
0 The complement of OPR[4].
1 The Channel A receiver interrupt output which is the complement
of ISR[1]. When in this mode OP4 acts as an open-drain output.
Note that this output is not masked by the contents of the IMR.
It is reset when the THR is loaded by the CPU, a pending
transmitter disable is executed, the transmitter is reset, or the
transmitter is disabled while in the underrun condition.
OPCR[3:2] – OP3 Output Select
This bit programs the OP3 output to provide one of the following:
00 The complement of OPR[3].
01 The counter/timer output, in which case OP3 acts as an
open-drain output. In the timer mode, this output is a square
wave at the programmed frequency. In the counter mode, the
output remains HIGH until terminal count is reached, at which
time it goes LOW. The output returns to the HIGH state when
the counter is stopped by a stop counter command. Note that
this output is not masked by the contents of the IMR.
10 The 1X clock for the Channel B transmitter, which is the clock
that shifts the transmitted data. If data is not being transmitted,
a free running 1X clock is output.
11 The 1X clock for the Channel B receiver, which is the clock that
samples the received data. If data is not being received, a free
running 1X clock is output.
SRA[2] – Channel A Transmitter Ready (TxRDYA)
This bit, when set, indicates that the THR is empty and ready to be
loaded with a character. This bit is cleared when the THR is loaded
by the CPU and is set when the character is transferred to the
transmit shift register. TxRDY is reset when the transmitter is
disabled and is set when the transmitter is first enabled, e.g.,
characters loaded into the THR while the transmitter is disabled will
not be transmitted.
SRA[1] – Channel A FIFO Full (FFULLA)
This bit is set when a character is transferred from the receive shift
register to the receive FIFO and the transfer causes the FIFO to
become full, i.e., all three FIFO positions are occupied. It is reset
when the CPU reads the RHR. If a character is waiting in the
2004 Mar 03
SCC68692
16
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
ACR[6:4] – Counter/Timer Mode And Clock Source Select
This field selects the operating mode of the counter/timer and its
clock source as shown in Table 5.
OPCR[1:0] – OP2 Output Select
This field programs the OP2 output to provide one of the following:
00 The complement of OPR[2].
01 The 16X clock for the Channel A transmitter. This is the clock
selected by CSRA[3:0], and will be a 1X clock if CSRA[3:0] =
1111.
10 The 1X clock for the Channel A transmitter, which is the clock
that shifts the transmitted data. If data is not being transmitted, a
free running 1X clock is output.
11 The 1X clock for the Channel A receiver, which is the clock that
samples the received data. If data is not being received, a free
running 1X clock is output.
Table 5. ACR [6:4] Field Definition
ACR – Auxiliary Control Register
ACR[7] – Baud Rate Generator Set Select
This bit selects one of two sets of baud rates to be generated by the
BRG.
Set 1:
50, 110, 134.5, 200, 300, 600, 1.05k, 1.2k, 2.4k, 4.8k, 7.2k, 9.6k, and 38.4k baud.
Set 2:
75, 110, 134.5, 150, 300, 600, 1.2k, 1.8k, 2.0k, 2.4k, 4.8k, 9.6k, and 19.2k baud.
50
75
110
134.5
150
200
300
600
1050
1200
1800
2000
2400
4800
7200
9600
14.4K
19.2K
28.8K
38.4K
57.6K
115.2K
ACTUAL 16X CLOCK (kHz)
0.8
1.2
1.759
2.153
2.4
3.2
4.8
9.6
16.756
19.2
28.8
32.056
38.4
76.8
115.2
153.6
230.4
307.2
460.8
614.4
921.2
1,843.2
MODE
Counter
CLOCK SOURCE
External (IP2)
001
Counter
TxCA – 1x clock of Channel A
transmitter
010
Counter
TxCB – 1x clock of Channel B
transmitter
011
Counter
Crystal or external (x1/CLK)
divided by 16
100
Timer (square wave)
External (IP2)
101
Timer (square wave)
External (IP2) divided by 16
110
Timer (square wave)
Crystal or external clock
(X1/CLK)
111
Timer (square wave)
Crystal or IP2 clock (X1/CLK)
divided by 16
ACR[3:0] – IP3, IP2, IP1, IP0 Change-of-State Interrupt Enable
This field selects which bits of the input port change register (IPCR)
cause the input change bit in the interrupt status register (ISR[7]) to
be set. If a bit is in the ‘on’ state the setting of the corresponding bit
in the IPCR will also result in the setting of ISR[7], which results in
the generation of an interrupt output if IMR[7] = 1. If a bit is in the
‘off’ state, the setting of that bit in the IPCR has no effect on ISR[7].
ERROR (%)
0
0
–0.069
0.059
0
0
0
0
–0.260
0
0
0.175
0
0
0
0
0
0
0
0
0
0
IPCR – Input Port Change Register
IPCR[7:4] – IP3, IP2, IP1, IP0 Change-of-State
These bits are set when a change-of-state, as defined in the input
port section of this data sheet, occurs at the respective input pins.
They are cleared when the IPCR is read by the CPU. A read of the
IPCR also clears ISR[7], the input change bit in the interrupt status
register. The setting of these bits can be programmed to generate
an interrupt to the CPU.
IPCR[3:0] – IP3, IP2, IP1, IP0 Change-of-State
These bits provide the current state of the respective inputs. The
information is unlatched and reflects the state of the input pins at the
time the IPCR is read.
ISR – Interrupt Status Register
This register provides the status of all potential interrupt sources.
The contents of this register are masked by the Interrupt Mask
Register (IMR). If a bit in the ISR is a ‘1’ and the corresponding bit in
the IMR is also a ‘1’, the INTRN output will be asserted (LOW). If the
corresponding bit in the IMR is a zero, the state of the bit in the ISR
has no effect on the INTRN output. Note that the IMR does not mask
the reading of the ISR – the true status will be provided regardless
of the contents of the IMR. The contents of this register are
initialized to H‘00’ when the DUART is reset.
NOTE: Duty cycle of 16X clock is 50% ±1%.
Asynchronous UART communications can tolerate frequency error
of 4.1% to 6.7% in a “clean” communications channel. The percent
of error changes as the character length changes. The above
percentages range from 5 bits not parity to 8 bits with parity and one
stop bit. The error with 8 bits no parity and one stop bit is 4.6%. If a
stop bit length of 9/16 is used, the error tolerance will approach 0
due to a variable error of up to 1/16 bit time in receiver clock phase
alignment to the start bit.
ISR[7] – Input Port Change Status
This bit is a ‘1’ when a change-of-state has occurred at the IP0, IP1,
IP2, or IP3 inputs and that event has been selected to cause an
interrupt by the programming of ACR[3:0]. The bit is cleared when
the CPU reads the IPCR.
The selected set of rates is available for use by the Channel A and
B receivers and transmitters as described in CSRA and CSRB.
Baud rate generator characteristics are given in Table 4.
2004 Mar 03
[6:4]
000
NOTE: Timer mode generates a squarewave.
Table 4. Bit Rate Generator Characteristics
Crystal or Clock = 3.6864MHz
BAUD RATE
SCC68692
17
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
ISR[6] – Channel B Change In Break
This bit, when set, indicates that the Channel B receiver has detected
the beginning or the end of a received break. It is reset when the CPU
issues a Channel B ‘reset break change interrupt’ command.
CTUR and CTLR – Counter/Timer Registers
The CTUR and CTLR hold the eight MSBs and eight LSBs,
respectively, of the value to be used by the counter/timer in either
the counter or timer modes of operation. The minimum value which
may be loaded into the CTUR/CTLR registers is H‘0002’. Note that
these registers are write-only and cannot be read by the CPU.
ISR[5] – Channel B Receiver Ready or FIFO Full
The function of this bit is programmed by MR1B[6]. If programmed
as receiver ready, it indicates that a character has been received in
Channel B and is waiting in the FIFO to be read by the CPU. It is set
when the character is transferred from the receive shift register to
the FIFO and reset when the CPU reads the RHR. If after this read
there are more characters still in the FIFO the bit will be set again
after the FIFO is ‘popped’. If programmed as FIFO full, it is set when
a character is transferred from the receive holding register to the
receive FIFO and the transfer caused the Channel B FIFO to
become full; i.e., all three FIFO positions are occupied. It is reset
when the CPU reads the RHR. If a character is waiting in the
receive shift register because the FIFO is full, the bit will be set
again when the waiting character is loaded into the FIFO.
In the timer (programmable divider) mode, the C/T generates a
square wave with a period of twice the value (in clock periods) of the
CTUR and CTLR. The waveform so generated is often used for a
data clock. The formula for calculating the divisor n to load to the
CTUR and CTLR for a particular 1X data clock is shown below:
n +
16
counter clock frequency
2
baud rate desired
Often this division will result in a non-integer number; 26.3, for
example. One can only program integer numbers in a digital divider.
Therefore, 26 would be chosen. This gives a baud rate error of
0.3/26.3 which is 1.14%; well within the ability asynchronous mode
of operation.
ISR[4] – Channel B Transmitter Ready
This bit is a duplicate of TxRDYB (SRB[2]).
If the value in CTUR and CTLR is changed, the current half-period
will not be affected, but subsequent half periods will be. The C/T will
not be running until it receives an initial ‘Start Counter’ command
(read at address A3–A0 = 1110). After this, while in timer mode, the
C/T will run continuously. Receipt of a start counter command (read
with A3–A0 = 1110) causes the counter to terminate the current
timing cycle and to begin a new cycle using the values in CTUR and
CTLR.
ISR[3] – Counter Ready.
In the counter mode, this bit is set when the counter reaches
terminal count and is reset when the counter is stopped by a stop
counter command.
In the timer mode, this bit is set once each cycle of the generated
square wave (every other time that the counter/timer reaches zero
count). The bit is reset by a stop counter command. The command,
however, does not stop the counter/timer.
The counter ready status bit (ISR[3]) is set once each cycle of the
square wave. The bit is reset by a stop counter command (read with
A3–A0 = H‘F’). The command however, does not stop the C/T. The
generated square wave is output on OP3 if it is programmed to be
the C/T output.
ISR[2] – Channel A Change in Break
This bit, when set, indicates that the Channel A receiver has
detected the beginning or the end of a received break. It is reset
when the CPU issues a Channel A ‘reset break change interrupt’
command.
In the counter mode, the C/T counts down the number of pulses
loaded into CTUR and CTLR by the CPU. Counting begins upon
receipt of a start counter command. Upon reaching terminal count
H‘0000’, the counter ready interrupt bit (ISR[3]) is set. The counter
continues counting past the terminal count until stopped by the CPU.
If OP3 is programmed to be the output of the C/T, the output
remains HIGH until terminal count is reached, at which time it goes
LOW. The output returns to the HIGH state and ISR[3] is cleared
when the counter is stopped by a stop counter command. The CPU
may change the values of CTUR and CTLR at any time, but the new
count becomes effective only on the next start counter commands. If
new values have not been loaded, the previous count values are
preserved and used for the next count cycle
ISR[1] – Channel A Receiver Ready Or FIFO Full
The function of this bit is programmed by MR1A[6]. If programmed
as receiver ready, it indicates that a character has been received in
Channel A and is waiting in the FIFO to be read by the CPU. It is set
when the character is transferred from the receive shift register to
the FIFO and reset when the CPU reads the RHR. If after this read
there are more characters still in the FIFO the bit will be set again
after the FIFO is ‘popped’. If programmed as FIFO full, it is set when
a character is transferred from the receive holding register to the
receive FIFO and the transfer caused the Channel A FIFO to
become full; i.e., all three FIFO positions are occupied. It is reset
when the CPU reads the RHR. If a character is waiting in the
receive shift register because the FIFO is full, the bit will be set
again when the ISR[0] and IMR waiting character is loaded into the
FIFO.
In the counter mode, the current value of the upper and lower 8 bits
of the counter (CTU, CTL) may be read by the CPU. It is
recommended that the counter be stopped when reading to prevent
potential problems which may occur if a carry from the lower 8 bits
to the upper 8 bits occurs between the times that both halves of the
counter are read. However, note that a subsequent start counter
command will cause the counter to begin a new count cycle using
the values in CTUR and CTLR.
ISR[0] – Channel A Transmitter Ready
This bit is a duplicate of TxRDYA (SRA[2]).
IMR – Interrupt Mask Register
The programming of this register selects which bits in the ISR
causes an interrupt output. If a bit in the ISR is a ‘1’ and the
corresponding bit in the IMR is also a ‘1’ the INTRN output will be
asserted. If the corresponding bit in the IMR is a zero, the state of
the bit in the ISR has no effect on the INTRN output. Note that the
IMR does not mask the programmable interrupt outputs OP3–OP7
or the reading of the ISR.
2004 Mar 03
SCC68692
IVR – Interrupt Vector Register
This register contains the interrupt vector. The register is initialized
to H‘0F’ by RESET. The contents of the register are placed on the
data bus when the DUART responds to a valid interrupt
acknowledge cycle.
18
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
RESET
tRES
SD00028
Figure 3. Reset Timing
tCSC
X1/CLK
tAS
A1–A4
tRWS
tRWH
RWN
tCSW
tAH
CSN
tDF
tDD
NOT
VALID
D0–D7
DATA VALID
tDA
tCSD
tDAL
DTACKN
tDAH
tDCR
tDAT
NOTE: DACKN low requires two rising edges of X1 clock after CSN is low.
SD00147
Figure 4. Bus Timing (Read Cycle)
tCSC
X1/CLK
tAS
A1–A4
RWN
tRWH
tRWS
tCSW
tAH
CSN
D0–D7
tDH
tDS
tCSD
DTACKN
tDAH
tDCW
tDAT
NOTE: DACKN low requires two rising edges of X1 clock after CSN is low.
SD00148
Figure 5. Bus Timing (Write Cycle)
2004 Mar 03
19
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
tCSC
X1/CLK
INTRN
IACKN
tDF
tDD
D0–D7
tCSD
tDAL
DTACKN
tDCR
tDAH
tDAT
NOTE: DACKN low requires two rising edges of X1 clock after CSN is low.
SD00149
Figure 6. Interrupt Cycle Timing
CSN
tPS
tPH
IP0–IP5
CSN
OP0–OP7
NEW DATA
OLD DATA
tPD
SD00150
Figure 7. Port Timing
RDN
OR
WRN
VM
tIR
VOL
INTERRUPT 1
OUTPUT
+0.5V
VOL
NOTES:
1. INTRN or OP3 – OP7 when used as interrupt outputs.
2. The test for open-drain outputs is intended to guarantee switching of the output transistor. Measurement of this response is referenced from themidpoint of the switching signal, VM, to a
point 0.5V above VOL. This point represents noise margin that assures true switching has occurred. Beyond this level, the effects of external circuitry and test environment are pronounced
and can greatly affect the resultant measurement.
SD00090
Figure 8. Interrupt Timing
2004 Mar 03
20
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
tCLK
tCTC
tRx
tTx
+5V
R1
1K
X1/CLK
CTCLK
RxC
TxC
X1
U1
RESISTOR REQUIRED
WHEN U1 IS A TTL DEVICE
tCLK
tCTC
tRx
tTx
X2
NC
SCC2698B
C1 = C2 = 24pF FOR CL = 20PF
X1
3pF
50 TO
150 KΩ
X2
TO INTERNAL CLOCK DRIVERS
3.6864MHz
4pF
NOTE:
C1 AND C2 SHOULD BE BASED ON MANUFACTURER’S SPECIFICATION. PARASITIC CAPACITANCE SHOULD
BE INCLUDED WITH C1 AND C2. R1 IS ONLY REQUIRED IF U1 WILL NOT DRIVE TO X1 INPUT LEVELS
TYPICAL CRYSTAL SPECIFICATION
FREQUENCY:
2 – 4MHZ
12 – 32pF
LOAD CAPACITANCE (CL):
TYPE OF OPERATION:
PARALLEL RESONANT, FUNDAMENTAL MODE
SD00137
Figure 9. Clock Timing
1 BIT TIME
(1 OR 16 CLOCKS)
TxC
(INPUT)
tTXD
TxD
tTCS
TxC
(1X OUTPUT)
SD00146
Figure 10. Transit Timing
2004 Mar 03
21
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
RxC
(1X INPUT)
tRXS
tRXH
RxD
SD00093
Figure 11. Receive Timing
TxD
D1
D2
D3
BREAK
D4
D6
TRANSMITTER
ENABLED
TxRDY
(SR2)
CSN
(WRITE)
D1
D2
D3
START
BREAK
D4
STOP
BREAK
CTSN1
(IP0)
D5 WILL
NOT BE
TRANSMITTED
D6
RTSN2
(OP0)
OPR(0) = 1
OPR(0) = 1
NOTES:
1. Timing shown for MR2(4) = 1.
2. Timing shown for MR2(5) = 1.
SD00118
Figure 12. Transmitter Timing
D1
RxD
D2
D3
D4
D5
D6
D7
D8
D6, D7, D8 WILL BE LOST
RECEIVER
ENABLED
RxRDY
(SR0)
FFULL
(SR1)
RxRDY/
FFULL
(OP4)2
CSN
(READ)
STATUS DATA
STATUS DATA STATUS DATA STATUS DATA
D5 WILL
BE LOST
D1
OVERRUN
(SR4)
D2
D3
D4
RESET BY COMMAND
RTS1
(OP0)
OPR(0) = 1
NOTES:
1. Timing shown for MR1(7) = 1.
SD00119
2. Shown for OPCR(4) and MR1(6) = 0.
Figure 13. Receiver Timing
2004 Mar 03
22
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
MASTER STATION
BIT 9
ADD#1 1
TxD
BIT 9
BIT 9
D0
SCC68692
ADD#2 1
0
TRANSMITTER
ENABLED
TxRDY
(SR2)
CSN
(WRITE)
MR1(4+3) = 11
MR1(2) = 1
ADD#1 MR1(2) = 0 D0
PERIPHERAL STATION
BIT 9
0
RxD
MR1(2) = 1 ADD#2
BIT 9
ADD#1 1
BIT 9
BIT 9
D0
BIT 9
ADD#2 1
0
0
RECEIVER
ENABLED
RxRDY
(SR0)
CSN
MR1(4:3) = 11
ADD#1
STATUS DATA
STATUS DATA
D0
ADD#2
SD00120
Figure 14. Wake-Up Mode
The CTS, RTS, CTS Enable Tx signals
2.7K
CTS (Clear To Send) is usually meant to be a signal to the
transmitter meaning that it may transmit data to the receiver. The
CTS input is on pin MPI. The CTS signal is active LOW; thus, it is
called CTS.
+5V
INTRN
50pF
750Ω
D0–D7
TxDA/B
OP0–OP7
RTS is usually meant to be a signal from the receiver indicating that
the receiver is ready to receive data. It is also active LOW and is,
thus, called RTSN. RTSN is on pin MP0. A receiver’s RTS output
will usually be connected to the CTS input of the associated
transmitter. Therefore, one could say that RTS and CTS are different
ends of the same wire!
2.15V
150pF
SD00151
Figure 15. Test Conditions on Outputs
MR2(4) is the bit that allows the transmitter to be controlled by the
CTS pin (MPI). When this bit is set to one AND the CTS input is
driven HIGH, the transmitter will stop sending data at the end of the
present character being serialized. It is usually the RTS output of the
receiver that will be connected to the transmitter’s CTS input. The
receiver will set RTS HIGH when the receiver FIFO is full AND the
start bit of the fourth character is sensed. Transmission then stops
with four valid characters in the receiver. When MR2(4) is set to one,
CTSN must be at zero for the transmitter to operate. If MR2(4) is set
to zero, the MP pin will have no effect on the operation of the
transmitter.
Output Port Notes
The output ports are controlled from four places: the OPCR register,
the OPR register, the MR registers and the command register. The
OPCR register controls the source of the data for the output ports
OP2 through OP7. The data source for output ports OP0 and OP1 is
controlled by the MR and CR registers. When the OPR is the source
of the data for the output ports, the data at the ports is inverted from
that in the OPR register. The content of the OPR register is
controlled by the “Set Output Port Bits Command” and the “Reset
Output Bits Command”. These commands are at E and F,
respectively. When these commands are used, action takes place
only at the bit locations where ones exist. For example, a one in bit
location 5 of the data word used with the “Set Output Port Bits”
command will result in OPR5 being set to one. The OP5 would then
be set to zero (VSS). Similarly, a one in bit position 5 of the data
word associated with the “Reset Output Ports Bits” command would
set OPR5 to zero and, hence, the pin OP5 to a one (VDD).
2004 Mar 03
MR1(7) is the bit that allows the receiver to control MP0. When MP0
is controlled by the receiver, the meaning of that pin will be RTS.
However, a point of confusion arises in that MP0 may also be
controlled by the transmitter. When the transmitter is controlling this
pin, its meaning is not RTS at all. It is, rather, that the transmitter has
finished sending its last data byte. Programming the MP0 pin to be
23
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
The test mode at address H‘2’ changes all transmitters and
receivers to the 1x mode and connects the output ports to some
internal nodes.
controlled by the receiver and the transmitter at the same time is
allowed, but would usually be incompatible.
RTS can also be controlled by the commands 1000 and 1001 in the
command register. RTS is expressed at the MP0 pin which is still an
output port. Therefore, the state of MP0 should be set LOW (either
by commands of the CR register or by writing to the Set Output
Ports Register) for the receiver to generate the proper RTS signal.
The logic at the output is basically a NAND of the MP0 bit register
and the RTS signal as generated by the receiver. When the RTS
flow control is selected via the MR(7) bit the state of the MP0
register is not changed. Terminating the use of “Flow Control” (via
the MR registers) will return the MP0 pin to the control of the MP0
register.
Table 6. Baud Rate
Normal BRG
ACR[7] = 0
ACR[7] = 1
ACR[7] = 0
ACR[7] = 1
0000
50
75
4,800
7,200
Transmitter Disable Note
The sequence of instructions enable transmitter — load transmit
holding register — disable transmitter will result in nothing being
sent if the time between the end of loading the transmit holding
register and the disable command is less that 3/16 bit time in the
16x mode or one bit time in the 1x mode. Also, if the transmitter,
while in the enabled state and underrun condition, is immediately
disabled after a single character is loaded to the transmit holding
register, that character will not be sent.
In general, when it is desired to disable the transmitter before the
last character is sent AND the TxEMT bit is set in the status register
(TxEMT is always set if the transmitter has underrun or has just
been enabled), be sure the TxRDY bit is active immediately before
issuing the transmitter disable instruction. TxRDY sets at the end of
the “start bit” time. It is during the start bit that the data in the
transmit holding register is transferred to the transmit shift register.
BRG Test
CSR[7:4]
0001
110
110
880
880
0010
134.5
134.5
1,076
1,076
0011
200
150
19.2K
14.4K
0100
300
300
28.8K
28.8K
0101
600
600
57.6K
57.6K
0110
1,200
1,200
115.2K
115.2K
0111
1,050
2,000
1,050
2,000
1000
2,400
2,400
57.6K
57.6K
1001
4,800
4,800
4,800
4,800
1010
7,200
1,800
57.6K
14.4K
1011
9,600
9,600
9,600
9,600
1100
38.4K
19.2K
38.4K
19.2K
1101
Timer
Timer
Timer
Timer
1110
I/O2 – 16X
I/O2 – 16X
I/O2 – 16X
I/O2 – 16X
1111
I/O2 – 1X
I/O2 – 1X
I/O2 – 1X
I/O2 – 1X
NOTE:
Each read on address H‘A’ will toggle the baud rate test mode.
When in the BRG test mode, the baud rates change as shown to the
left. This change affects all receivers and transmitters on the
DUART. See “Extended baud rates for SCN2681, SCN68681,
SCC2691, SCC2692, SCC68681 and SCC2698B” in application
notes elsewhere in this publication
Non-standard baud rates are available as shown in Table 6 below,
via the BRG Test function.
Receiver Reset in the Normal Mode (Receiver Enabled)
Reset can be accomplished easily by issuing a receiver software or hardware reset followed by a receiver enable. All receiver data,
status and programming will be preserved and available before reset. The reset will NOT affect the programming.
Receiver Reset in the Wake-Up Mode (MR1[4:3] = 11)
Reset can also be accomplished easily by first exiting the wake-up mode (MR1[4:3] = 00 or 01 or 10), then issuing a receiver software or
hardware reset followed by a wake-up re-entry (MR1[4:3] = 11). All receiver data, status and programming will be preserved and
available before reset. The reset will NOT affect other programming.
The reason for this is the receiver is partially enabled when the parity bits are at ‘11’. Thus the receiver disable and reset is bypassed by
the partial enabling of the receiver.
SD00097
2004 Mar 03
24
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
DIP40: plastic dual in-line package; 40 leads (600 mil)
2004 Mar 03
25
SCC68692
SOT129-1
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
PLCC44: plastic leaded chip carrier; 44 leads
2004 Mar 03
SCC68692
SOT187-2
26
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
REVISION HISTORY
Rev
Date
Description
_3
20040303
Product data (9397 750 13001). Supersedes data of 1998 Sep 04 (9397 750 04361).
Modifications:
• Remove all references to cerdip package offering (SCC68692C1F40 and SCC68692E1F40 parts are discontinued).
_2
19980904
Product specification (9397 750 04361). ECN 853-0977 19971 of 04 September 1998.
Supersedes data of 1995 May 01.
_1
19950501
Product specification. ECN 853-0977 15179 of 01 May 1995.
2004 Mar 03
27
Philips Semiconductors
Product data
Dual asynchronous receiver/transmitter (DUART)
SCC68692
Data sheet status
Level
Data sheet status [1]
Product
status [2] [3]
Definitions
I
Objective data
Development
This data sheet contains data from the objective specification for product development.
Philips Semiconductors reserves the right to change the specification in any manner without notice.
II
Preliminary data
Qualification
This data sheet contains data from the preliminary specification. Supplementary data will be published
at a later date. Philips Semiconductors reserves the right to change the specification without notice, in
order to improve the design and supply the best possible product.
III
Product data
Production
This data sheet contains data from the product specification. Philips Semiconductors reserves the
right to make changes at any time in order to improve the design, manufacturing and supply. Relevant
changes will be communicated via a Customer Product/Process Change Notification (CPCN).
[1] Please consult the most recently issued data sheet before initiating or completing a design.
[2] The product status of the device(s) described in this data sheet may have changed since this data sheet was published. The latest information is available on the Internet at URL
http://www.semiconductors.philips.com.
[3] For data sheets describing multiple type numbers, the highest-level product status determines the data sheet status.
Definitions
Short-form specification — The data in a short-form specification is extracted from a full data sheet with the same type number and title. For detailed information see
the relevant data sheet or data handbook.
Limiting values definition — Limiting values given are in accordance with the Absolute Maximum Rating System (IEC 60134). Stress above one or more of the limiting
values may cause permanent damage to the device. These are stress ratings only and operation of the device at these or at any other conditions above those given
in the Characteristics sections of the specification is not implied. Exposure to limiting values for extended periods may affect device reliability.
Application information — Applications that are described herein for any of these products are for illustrative purposes only. Philips Semiconductors make no
representation or warranty that such applications will be suitable for the specified use without further testing or modification.
Disclaimers
Life support — These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be
expected to result in personal injury. Philips Semiconductors customers using or selling these products for use in such applications do so at their own risk and agree
to fully indemnify Philips Semiconductors for any damages resulting from such application.
Right to make changes — Philips Semiconductors reserves the right to make changes in the products—including circuits, standard cells, and/or software—described
or contained herein in order to improve design and/or performance. When the product is in full production (status ‘Production’), relevant changes will be communicated
via a Customer Product/Process Change Notification (CPCN). Philips Semiconductors assumes no responsibility or liability for the use of any of these products, conveys
no license or title under any patent, copyright, or mask work right to these products, and makes no representations or warranties that these products are free from patent,
copyright, or mask work right infringement, unless otherwise specified.
 Koninklijke Philips Electronics N.V. 2004
All rights reserved. Printed in U.S.A.
Contact information
For additional information please visit
http://www.semiconductors.philips.com.
Fax: +31 40 27 24825
Date of release: 03-04
For sales offices addresses send e-mail to:
[email protected]
Document order number:
2004 Mar 03
28
9397 750 13001
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