B&B Electronics 3PCIU4 - Manual (Page 75)

Troubleshooting MIport Cards
Manual Documentation Number 3PCIoUx-1008 Chapter 9 69
RS-422/485 Operation
1. Check your pinouts. In RS-422 or RS-485 mode the "A" lines
should match your "A" or " −" lines. "B" lines should match your
"B" or "+" lines.
Note: RS-422/485 pinouts are non-standard.
2. Make sure you have RTS Control set to the correct mode: Normal
for RS-232, RS-485 Mode for RS-485. RS-422 mode works in
either setting if the mode jumpers are set correctly.
Checking the MIport Card
Using ComTest and a loopback connection, you can check the operation of
your MIport card separate from the rest of your communications system.
Note: Refer to Appendix C for information on how to install and use
ComTest
1. A loopback connection for RS-232 connects the Transmit output to
the Receive input (pins #2 & #3 on the DB-9 connector). Use
connections below to check all.
Figure 52. RS-232 Loopback w/Handshaking Connections
2. For RS-422 or 4-wire RS-485, connect the TD(A) to RD(A) and the
TD(B) to RD(B). Then use the ComTest program to send
characters, and observe the characters being received.