RS-422 over NI 8431

Hi everybody,

I'm using the NI-8431 to communicate with an instrument from a PC.

The instrument uses 4 channels - 3 RS-485 half duplex at 1 Mbit/Sec and 1 RS-422 at 2 Mbit/Sec. On the RS-422's channel the PC sends 150 byte at 30 Hz and the instrument sends two messages, one of 231 bytes and the other of 150 bytes at 60 Hz (total of 120 messages/sec). I have problem to receive the incoming message whenever the outgoing message is transmitted. When I inspect it using Port Monitor application, I see that whenever an outgoing message is sent, I receive only partial (about 150 bytes) out of the 231 expected bytes. Any information/suggestion about the issue?

thanks in advance,

Nir Gil