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Chapter 3
Pin #
Pin #
DB9
7
4
8
9
9
5
10
NC
11
1
(COM4)
12
6
13
2
14
7
15
3
16
8
17
4
18
9
19
5
20
NC
Notes: The shaded area denotes power or ground. Signals are listed in the following order: RS232
followed by RS485/RS422
LittleBoard 700
Signal
Description
DTR3*
Data Terminal Ready 3 – Serial port 3 indicator that port is powered,
initialized, and ready. Used as hardware handshake with DSR3 for
overall readiness to communicate. Designed for direct input to external
RS232 driver.
RI3*
Ring Indicator 3 – Indicator to serial port 3 that external modem is
detecting a ring condition. Used by software to initiate operations to
answer and open the communications channel. Designed for direct
input from external RS232 receiver (whose input is typically not
connected in direct connect environments)
GND
Ground
KEY/
Key
NC
Not connected
NC
Not connected
NC
Not connected
RXD4
Receive Data 4 – Serial port 4 receive data in
RX4-
RX4- – If in RS485 or RS422 mode, this pin is Receive Data 4 -.
RTS4*
Request To Send 4 – Indicator to serial output port 4 is ready to transmit
data. Used as hardware handshake with CTS4 for low level flow
TX4+
control.
TX4+ – If in RS485 or RS422 mode, this pin is Transmit Data 4 +.
TXD4
Transmit Data 4 – Serial port 4 transmit data out
TX4-
TX4- – If in RS485 or RS422 mode, this pin is Transmit Data 4 -.
CTS4*
Clear To Send 4 – Indicator to serial port 4 that external serial
communications device is ready to receive data. Used as hardware
handshake with RTS4 for low level flow control.
RX4+
RX4+ – If in RS485 or RS422 mode, this pin is Receive Data 4 +.
NC
Not connected
NC
Not connected
GND
Ground
NC
Not connected
Reference Manual
Hardware
43
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