Teknor Industrial Computers TEK-AT4LVG Technical Reference Manual page 105

Serial Port 2 (J7) RS-485
If Serial Port 2 is configured for RS-485 operation, it can support either full-duplex or
party line communication.
Full Duplex Operation: Upon power-up or reset, the RS-485 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: 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 W16 jumper). This
allows the transceiver (pins 3 and 4 of J6) 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 R110 and R112 must be installed only on the
boards at both ends of the network.
The following table shows this connector's pinout:
TABLE 9-3: Serial Port 2 (J7) RS-485 - Pinout
Pin Number
Signal Flow
Signal
DCD I
RXD(-) I/O
TXD(-) O
DTR O
GND -
Installing Peripherals
Pin Number
Signal Flow
Signal
1 2 I DSR
3 4 I/O RXD(+)
5 6 I TXD(+)
7 8 I RI
9 10 - Not Used
9-6