Specifications

Chapter 3 Hardware
LittleBoard 735 Reference Manual 25
Note: The shaded areas denote power or ground. Signals are listed in the table with RS232 first, followed
by RS485/RS422. The signals marked with * = Negative true logic.
11 1
(COM4)
DCD4* Data Carrier Detect 4 – Indicates external serial communications
device is detecting a carrier signal (i.e., a communication channel is
currently open). In direct connect environments, this input will be
driven by DTR4 as part of the DTR/DSR handshake.
12 6 DSR4* Data Set Ready 4 – Indicates external serial communications device is
powered, initialized, and ready. Used as hardware handshake with
DTR4 for overall readiness to communicate.
13 2 RXD4
RX4-
Receive Data 4 – Serial port 4 receive data in
RX4- – If in RS485 or RS422 mode, this pin is Receive Data 4 -.
14 7 RTS4*
TX4+
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 control.
TX4+ – If in RS485 or RS422 mode, this pin is Transmit Data 4 +.
15 3 TXD4
TX4-
Transmit Data 4 – Serial port 4 transmit data out
TX4- – If in RS485 or RS422 mode, this pin is Transmit Data 4 -.
16 8 CTS4*
RX4+
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+ – If in RS485 or RS422 mode, this pin is Receive Data 4 +.
17 4 DTR4* Data Terminal Ready 4 – Indicates this Serial port is powered,
initialized, and ready. Used as hardware handshake with DSR4 for
overall readiness to communicate.
18 9 RI4* Ring Indicator 4 – Indicates external serial communications device is
detecting a ring condition. Used by software to initiate operations to
answer and open the communications channel.
19 5
GND Ground
20 NC NC Not connected
Table 3-6. Serial B Interface Pin Signals (J12) (Continued)