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42 CME34BT cpuModule
BDM-610000088 Rev A
Dual Serial Port Modes
The serial port connectors can be configured as dual serial ports in the BIOS. This enhancement in dual
RS-232 comes at the cost of losing the DSR and DTR signals, which are only available in single RS-232
mode.
The mapping between the connectors and COM port numbers is shown in Table 16. The supported
combinations of serial port modes are listed in Table 17, which also includes a reference to the
corresponding connector pinout.
Table 16 Dual Serial Port Connections
Connector
COM A
COM B
CN7
COM 1
COM 3
CN8
COM 2
COM 4
Table 17 Dual Serial Port Modes
COM A
COM B
Pinout
Reference
Echo Mode
RS-232
RS-232
—
RS-422
RS-422
—
RS-485
RS-485
echo canceled
RS-485
RS-485
with echo
1
1. Dual RS-485 mode with echo uses dual RS-422 mode pinout
WARNING
The dual serial port mode pinouts of the COM ports are
not
compatible with
previous generations of RTD cpuModules.
Note
The cpuModule has 120 Ohm termination resistors. Termination is usually necessary
on all RS-422 receivers and at the ends of the RS-485 bus. Termination resistors can be
enabled in the BIOS setup utility. When termination is enabled in dual port mode, it is
enabled for both ports.
Table 18 COM A (RS-232) and COM B (RS-232)
Pin
Signal
Function
In/Out
DB-9
1
DCD1
COM A - Data Carrier Detect
in
1
2
CTS1
COM A - Clear To Send
in
6
3
RXD1
COM A - Receive Data
in
2
4
TXD2
COM B - Transmit Data
out
7
5
TXD1
COM A - Transmit Data
out
3
6
RXD2
COM B - Receive Data
in
8
7
RTS1
COM A - Request To Send
out
4
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