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Chapter 3 Hardware
46 Reference Manual LittleBoard 550
Pin # Pin #
DB9
Signal Description
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 – Indicates Serial 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 – Indicates 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 Serial port 4 is powered, initialized,
and ready. Used as hardware handshake with DSR4 for overall readiness
to communicate.
18 9 NC Not connected (Ring Indicator 4)
19 5 GND Ground
20 NC NC Not connected
Notes: The shaded area denotes power or ground. Signals are listed in the following order: RS232
followed by RS485/RS422