06-20-2013 09:26 AM
It's a USB/Serial converter.
06-20-2013 09:29 AM
buickgn,
This may be a problem with the USB converter/driver. Suggest you modify your vi to use a VISA Write to write out your known good query string, wait and then read the expected number of bytes and see what happens.
06-20-2013 10:08 AM - edited 06-20-2013 10:17 AM
Wayne,
It works fine with the Modbus Poll program which leads me to believe it's not a driver issue. I tried your suggestion here:
It sends the right command, however, in the "Read Buffer" it just repeats the command I sent.
06-20-2013 10:17 AM
buickgn,
I don't think you need the carrige return on the end of the write string.
06-20-2013 10:18 AM - edited 06-20-2013 10:21 AM
You're right, I got rid of that. Still repeating the request. Here's a screenshot of the trace:
06-20-2013 10:29 AM
Is the written command being echo'd by the serial adapter? What happens if you try to read more characters with the simple read/write string vi?
06-20-2013 10:35 AM
If I set it to 17, I get: 0203 0002 0002 65F8 0203 0439 0F7F 7394 79. Anything larger than 17 and it throws a timeout.
06-20-2013 10:43 AM
Wayne,
That was the issue, it's sending back the correct response after it echos the request. I guess the Modbus library doesn't play nice with this particular usb/serial converter!
06-20-2013 10:45 AM
Can you disable the echo? Any driver settings?
06-20-2013 10:51 AM
It doesn't look like it. I'm in device manager looking at all the settings and don't see anything to enable/disable the echo.