INTEGRATED CIRCUITS
SCN2681
Dual asynchronous receiver/transmitter
(DUART)
Product specification
Supersedes data of 1995 May 01
IC19 Data Handbook
1998 Sep 04
Philips
Semiconductors
Philips Semiconductors
Product specification
Dual asynchronous receiver/transmitter (DUART)
SCN2681
DESCRIPTION
The Philips Semiconductors SCN2681 Dual Universal
Asynchronous Receiver/Transmitter (DUART) is a single-chip
MOS-LSI communications device that provides two independent
full-duplex asynchronous receiver/transmitter channels in a single
package. It interfaces directly with microprocessors and may be
used in a polled or interrupt driven system.
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.
Each receiver is quadruply 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 buffer of the receiving device
is full.
Also provided on the SCN2681 are a multipurpose 7-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.
The SCN2681 is available in three package versions: 40-pin and
28–pin, both 0.6” wide DIPs; a compact 24-pin 0.4” wide DIP; and a
44-pin PLCC.
•
16-bit programmable Counter/Timer
–
Non-standard rates to 115.2Kb
–
One user-defined rate derived from programmable
timer/counter
–
External 1X or 16X clock
•
Parity, framing, and overrun error detection
•
False start bit detection
•
Line break detection and generation
•
Programmable channel mode
–
Normal (full-duplex)
–
Automatic echo
–
Local loopback
–
Remote loopback
•
Multi-function programmable 16-bit counter/timer
•
Multi-function 7-bit input port
–
Can serve as clock or control inputs
–
Change of state detection on four inputs
–
100kΩ typical pull-up resistor
•
Multi-function 8-bit output port
–
Individual bit set/reset capability
–
Outputs can be programmed to be status/interrupt signals
•
Versatile interrupt system
–
Single interrupt output with eight maskable interrupting
conditions
–
Output port can be configured to provide a total of up to six
separate wire-ORable interrupt outputs
FEATURES
•
Dual full-duplex asynchronous receiver/transmitter
•
Quadruple buffered receiver data registers
•
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
•
Programmable baud rate for each receiver and transmitter
selectable from:
–
22 fixed rates: 50 to 115.2k baud
•
Maximum data transfer: 1X – 1MB/sec, 16X – 125kB/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
•
Single +5V power supply
•
Commercial and industrial temperature ranges available
•
DIP and PLCC packages
ORDERING INFORMATION
ORDER CODE
DESCRIPTION
Commercial
V
CC
= +5V +5%, T
A
= 0°C to +70°C
Plastic DIP
24-Pin
1
28-Pin
2
40-Pin
2
SCN2681AC1N24
SCN2681AC1N28
SCN2681AC1N40
Plastic LCC
Not available
Not available
Not available
SCN2681AC1A44
Plastic DIP
SCN2681AE1N24
SCN2681AE1N28
SCN2681AE1N40
Not available
Industrial
V
CC
= +5V +10%, T
A
= -40°C to +85°C
Plastic LCC
Not available
Not available
Not available
SCN2681AE1A44
44-Pin
Not available
NOTES:
1. 400mil-wide Dual In-Line Package
2. 600mil-wide Dual In-Line Package
1998 Sep 04
2
853–1077 19970
Philips Semiconductors
Product specification
Dual asynchronous receiver/transmitter (DUART)
SCN2681
PIN CONFIGURATIONS
A0
IP3
A1
IP1
A2
A3
IP0
WRN
1
2
3
4
5
6
7
8
40 V
CC
39 IP4
38 IP5
37 IP6
36 IP2
35 CEN
34 RESET
33 X2
32 X1/CLK
31 RXDA
DIP
TXDB 11
OP1 12
OP3
13
30 TXDA
29 OP0
28 OP2
27 OP4
26 OP6
25 D0
24 D2
23 D4
22 D6
21 INTRN
A0
A1
A2
A3
WRN
RDN
RXDB
TXDB
OP1
D1
D3
1
2
3
4
5
6
7
DIP
8
9
10
11
21 TXDA
20 OP0
19 D0
18 D2
17 D4
16 D6
GND 12
GND 14
15 INTRN
28 V
CC
27 IP2
26 CEN
25 RESET
24 X2
23 X1/CLK
22 RXDA
A1
A2
A3
WRN
RDN
RXDB
TXDB
D1
D3
D5
1
2
3
4
5
6
DIP
7
8
9
10
18
17
16
15
14
13
24
23
22
21
20
19
A0
V
CC
CEN
RESET
X1/CLK
RXDA
TXDA
D0
D2
D4
D6
INTRN
RDN 9
RXDB 10
OP5 14
OP7 15
D1 16
D3 17
D5 18
D7 19
GND 20
D5 12
D7
13
D7 11
PIN/FUNCTION
INDEX
CORNER
7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
NC
A0
IP3
A1
IP1
A2
A3
IP0
WRN
RDN
RXDB
NC
TXDB
OP1
OP3
OP5
OP7
D1
D3
D5
D7
GND
PIN/FUNCTION
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
RESET
CEN
IP2
IP6
IP5
IP4
V
CC
6
1
40
39
PLCC
17
18
TOP VIEW
28
29
SD00084
Figure 1. Pin Configurations
1998 Sep 04
3
Philips Semiconductors
Product specification
Dual asynchronous receiver/transmitter (DUART)
SCN2681
PIN DESCRIPTION
SYMBOL
D0–D7
CEN
APPLICABLE
40/44
X
X
28
X
X
24
X
X
TYPE
I/O
I
NAME AND FUNCTION
Data Bus:
Bidirectional 3-State data bus used to transfer commands, data and status be-
tween 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 WRN, RDN and A0-A3 inputs. When
High, places the D0-D7 lines in the 3-State condition.
Write Strobe:
When Low and CEN is also Low, the contents of the data bus is loaded into
the addressed register. The transfer occurs on the rising edge of the signal.
Read Strobe:
When Low and CEN is also Low, causes the contents of the addressed regis-
ter to be presented on the data bus. The read cycle begins on the falling edge of RDN.
Address Inputs:
Select the DUART internal registers and ports for read/write operations.
Reset:
A High level clears internal registers (SRA, SRB, IMR, ISR, OPR, OPCR), puts
OP0–OP7 in the High state, stops the counter/timer, and puts Channels A and B in the inac-
tive state, with the TxDA and TxDB outputs in the mark (High) state. Clears Test modes, sets
MR pointer to MR1.
Interrupt Request:
Active-Low, open-drain, output which signals the CPU that one or more
of the eight maskable interrupting conditions are true.
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 7, Clock Timing.
Crystal 2:
Crystal connection. See Figure 7. 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 oper-
ating in local loopback mode. “Mark” is High, “space” is Low.
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 oper-
ating in local loopback mode. “Mark” is High, “space” is Low.
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 Chan-
nel 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, RxRDYA/FFULLA
output.
Output 5:
General purpose output or Channel B open-drain, active-Low, RxRDYB/FFULLB
output.
Output 6:
General purpose output or Channel A open-drain, active-Low, TxRDYA output.
Output 7:
General purpose output or Channel B open-drain, active-Low, TxRDYB output.
Input 0:
General purpose input or Channel A clear to send active-Low input (CTSAN). Pin
has an internal V
CC
pull-up device supplying 1 to 4
mA
of current.
Input 1:
General purpose input or Channel B clear to send active-Low input (CTSBN). Pin
has an internal V
CC
pull-up device supplying 1 to 4
mA
of current.
Input 2:
General purpose input or counter/timer external clock input. Pin has an internal V
CC
pull-up device supplying 1 to 4
mA
of current.
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 V
CC
pull-up device supplying 1 to 4
mA
of current.
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 V
CC
pull-up device supplying 1 to 4
mA
of current.
WRN
RDN
A0–A3
RESET
X
X
X
X
X
X
X
X
X
X
X
X
I
I
I
I
INTRN
X1/CLK
X
X
X
X
X
X
O
I
X2
RxDA
RxDB
TxDA
X
X
X
X
X
X
X
X
X
X
X
I
I
I
O
TxDB
X
X
X
O
OP0
OP1
OP2
OP3
OP4
OP5
OP6
OP7
IP0
IP1
IP2
IP3
X
X
X
X
X
X
X
X
X
X
X
X
X
X
O
O
O
O
O
O
O
O
I
I
X
I
I
IP4
X
I
1998 Sep 04
4
Philips Semiconductors
Product specification
Dual asynchronous receiver/transmitter (DUART)
SCN2681
PIN DESCRIPTION
(Continued)
SYMBOL
IP5
APPLICABLE
40/44
X
28
24
TYPE
I
NAME AND FUNCTION
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 V
CC
pull-up device supplying 1 to 4
mA
of current.
Input 6:
General purpose input or Channel B receiver external clock input (RxCB). 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 V
CC
pull-up device supplying 1 to 4
mA
of current.
Power Supply:
+5V supply input.
Ground
IP6
X
I
V
CC
GND
X
X
X
X
I
I
ABSOLUTE MAXIMUM RATINGS
1
SYMBOL
T
A
T
STG
PARAMETER
Operating ambient temperature
Storage temperature range
All voltages with respect to ground
3
range
2
RATING
See Note 4
-65 to +150
-0.5 to +6.0
UNIT
°C
°C
V
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 based on +150
o
C maximum junction temperature.
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. See Ordering information table for applicable operating temperature range and V
CC
supply range.
DC ELECTRICAL CHARACTERISTICS
1, 2, 3
T
A
= -40°C to +85°C, V
CC
= +5.0V
"
10%
SYMBOL
V
IL
V
IH
V
IH
V
IH
V
OL
V
OH
V
OH
I
IL
I
LL
I
X1L
I
X1H
I
X2L
I
X2H
I
OC
I
OCC
PARAMETER
Input low voltage
Input high voltage (except X1/CLK)
5
Input high voltage (except X1/CLK)
4
Input high voltage (X1/CLK)
Output low voltage
Output high voltage (except o.d. outputs)
5
Output high voltage (except o.d. outputs)
4
Input leakage current
Data bus 3-stage leakage current
X1/CLK low input current
X1/CLK high input current
X2 low input current
X2 high input current
Open-collector output leakage current
Power supply current
TEST CONDITIONS
LIMITS
Min
2
2.5
4
0.4
2.4
2.9
-10
-10
-4
-3
-1
0
-100
0
-10
-2
-1.5
0.2
3.5
-30
+30
10
10
0
0
1
10
0
100
10
150
175
Typ
Max
0.8
UNIT
V
V
V
V
V
V
V
µA
µA
mA
mA
mA
mA
µA
µA
µA
mA
mA
I
OL
= 2.4mA
I
OH
= -400µA
I
OH
= -400µA
V
IN
= 0 to V
CC
V
O
= 0.4 to V
CC
V
IN
= 0, X2 grounded
V
IN
= 0, X2 floated
V
IN
= V
CC
, X2 grounded
V
IN
= V
CC
, X2 floated
V
IN
= 0, X1/CLK floated
V
IN
= V
CC
, X1/CLK floated
V
O
= 0.4 to V
CC
0°C to +70°C version
-40°C to +85°C version
NOTES:
1. Parameters are valid over specified temperature range. See Ordering information table for applicable operating temperature range and V
CC
supply range.
2. All voltage measurements are referenced to ground (GND). For testing, all inputs except X1/CLK swing between 0.4V and 2.4V with a
transition time of 20ns maximum. For X1/CLK this swing is between 0.4V and 4.4V. All time measurements are referenced at input voltages
of 0.8V and 2.0V as appropriate.
3. Typical values are at +25°C, typical supply voltages, and typical processing parameters.
4. T
A
< 0°C
5. T
A
> 0°C
1998 Sep 04
5
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