Teknor Industrial Computers PCI-993, Technical Reference Manual

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Serial & Parallel Ports 10-5
Serial Port 2 (J7) RS485/RS422
If Serial Port 2 is configured for RS485 operation, it can support either full-duplex or
party line communication.
Full Duplex Operation (RS422): Upon power-up or reset, the COM2 interface circuits
are automatically configured for full duplex operation. Pins 3 and 4 of J7 act as the
receiver lines and pins 5 and 6 act as the transmitter lines.
Party Line Operation (RS485): In order to enable party line operation, the user must
first write "1" to bit 3 at I/O address 190H (or at 290H or 390H depending on W9
jumper). This allows the transceiver (pins 3 and 4 of J7) to be controlled by the RTS
signal. Upon power-up or reset, the transceiver is by default in "receiver mode" in
order to prevent unwanted perturbation on the line.
In party line operation, termination resistors R84 and R85 must be installed only on the
boards at both ends of the network.
The following table shows this connector's pin-out:
TABLE 10-3: Serial Port 2 (J7) RS485/RS422 - Pin-Out
Pin
Number Signal
Flow Signal Pin
Number Signal
Flow Signal
1 I DCD 2 I DSR
3 I/O RXD(-) 4 I/O RXD(+)
5 O TXD(-) 6 I TXD(+)
7 O DTR 8 I RI
9 - GND 10 - Not Used