![](http://datasheet.mmic.net.cn/NXP-Semiconductors/SCC68681C1N40-112_datasheet_99670/SCC68681C1N40-112_4.png)
Philips Semiconductors
Product data
SCC68681
Dual asynchronous receiver/transmitter (DUART)
2004 Apr 06
4
SYMBOL
NAME AND FUNCTION
TYPE
PIN
SYMBOL
NAME AND FUNCTION
TYPE
DIP40
PLCC44
X1/CLK
36
32
I
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 8, Clock Timing.
X2
37
33
I
Crystal 2: Crystal connection. See Figure 8. If a crystal is not used it is best to keep this pin not
connected. It must not be grounded.
RxDA
35
31
I
Channel A Receiver Serial Data Input: The least significant bit is received first. ‘Mark’ is HIGH,
‘space’ is LOW.
RxDB
11
10
I
Channel B Receiver Serial Data Input: The least significant bit is received first. ‘Mark’ is HIGH,
‘space’ is LOW.
TxDA
33
30
O
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.
TxDB
13
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
32
29
O
Output 0: General purpose output or Channel A request to send (RTSAN, active-LOW). Can be
deactivated automatically on receive or transmit.
OP1
14
12
O
Output 1: General purpose output or Channel B request to send (RTSBN, active-LOW). Can be
deactivated automatically on receive or transmit.
OP2
31
28
O
Output 2: General purpose output, or Channel A transmitter 1
× or 16× clock output, or Channel A
receiver 1
× clock output.
OP3
15
13
O
Output 3: General purpose output or open-drain, active-LOW counter/timer interrupt output or
Channel B transmitter 1
× clock output, or Channel B receiver 1× clock output.
OP4
30
27
O
Output 4: General purpose output or Channel A open-drain, active-LOW, RxRDYA/FFULLA
interrupt output.
OP5
16
14
O
Output 5: General purpose output or Channel B open-drain, active-LOW, RxRDYB/FFULLB
interrupt output.
OP6
29
26
O
Output 6: General purpose output or Channel A open-drain, active-LOW, TxRDYA interrupt
output.
OP7
17
15
O
Output 7: General purpose output, or Channel B open-drain, active-LOW, TxRDYB interrupt
output.
IP0
8
7
I
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 A of current.
IP1
5
4
I
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 A of current.
IP2
40
36
I
Input 2: General purpose input, or Channel B receiver external clock input (RxCB), or
counter/timer external clock input. 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
A of current.
IP3
3
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 A of current.
IP4
43
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 A of current.
IP5
42
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 A of current.
VCC
44
40
I
Power Supply: +5 V supply input.
GND
22
20
I
Ground.
NC
1, 12,
23, 34
–
Not connected.