B&B Electronics 3PCIU4 - Manual (Page 17)

Serial Card Setup
Manual Documentation Number 3PCIoUx-1008 Chapter 2 11
Setting the DIP Switches on RS-232/422/485 Ports
Set the DIP switches to configure the desired operating mode as follows:
422/485
TX On
RX On
232
TX SD
RX SD
Switch 1
Switch 2
Switch 3
RS-232 Mode
422/485
TX On
RX On
232
TX SD
RX SD
RS-422 Mode
422/485
TX On
RX On
232
TX SD
RX SD
4-wire RS-485 Mode
422/485
TX On
RX On
232
TX SD
RX SD
2-wire RS-485 Mode
Figure 5. RS-232/422/485 DIP Switch Settings.
DIP Switch 1 (RS-232/422/485 ports)
The top DIP switch (1) configures the port for RS-232 or RS-422/485
operation. This switch is the only one that is required to be set for RS-232
operation. The positions of switches 2 and 3 do not matter when switch 1 is
set for RS-232 operation.
DIP Switch 2 (RS-232/422/485 ports)
The middle DIP switch (2) configures the port for RS-485 or RS-422
operation. For RS-422 operation (which uses two wire pairs and sends point-
to-point or point-to-multipoints) the transmitter can be enabled all the time.
Placing the middle DIP switch in the TX ON position accomplishes this.
For RS-485 operation the middle DIP switch is placed in the TX SD position.
In this position the transmitter is only enabled when data is being sent. The
transmitter is tri-stated when not sending data, allowing other transmitters on
the communications line to transmit without interference.