I've been in that same situation with laboratoy equipment a lot. so I built a serial sniffer cable to try to understand communication issues. Here's a readme that I put together. I've also got a rough labview VI that gets data from a pair of serial ports. I'm hesitant to include the VI because it's pretty incomplete and was just enough to get the job done.
Hope this helps,
Sheldon
********************** readme file **********************
This sniffer uses a serial breakout cable and a pair of serial ports to read network traffic across a serial link.
The serial cable is built as follows:
This cable has four connectors, all are 9 pin D connectors. A pair of them (male and female) are a pass-through and are hooked in line with the original serial link. The second pair of connectors forms a sniffer pair which will direct host write commands to one serial port and direct device write commands to another serial port.
The main cable is just a serial pass-through cable which has pin 1 male to pin 1 female etc for all 9 pins. There is a second par of cables which do the sniffing. Both of these cables are two wire cables, with a wire going from pin 2 on the pass-through cable to pin 2 on the sniffer connector, the second wire is the ground reference and goes from pin 5 on the pass-through cable to pin 5 on the sniffer connector. The second sniffer connector has a wire going from pin 3 on the pass-through cable to pin 2 on the sniffer connector. The second wire goes from pin 5 on the pass-through connector to pin 5 on the sniffer connector.
Diagram (extra control wires ommitted for clarity):
Host: Device:
2 ----------------------------------- 2
|
3 ---)------------------------------- 3
| |
5 ---)-----------------------)------- 5
| | | |
| | | |
| | | |
2 5 2 5
Device Sniff Host Sniff
The device sniff and host sniff connectors are attached to a pair of serial ports. The labview code provided here listens to the traffic on both ports and displays and logs the bytes sent. Any application which can listen to both
serial ports can be used however.
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