communication problem with USB-485 converter?

[rbj]

I have recently purchased a single channel usb-485 converter for use with a series of OPTO22 B1 and B2 brainboards.  I have successfuly communicated with an identical set of boards that were converted using different hardware so I know the strings I am sending are correct.  I also know the boards are working because there is an antique IMB computer (older than me) that currently operates this set of boards.  I have checked the wiring of the boards and it appears consistent with rs485 and the wiring instructions from opto22.  I have attempted to send strings through both labview and the "communicate with instruments" program in MAX, in both cases there was no communication with the devices, based on the "recive" light on the opto boards the data is not even making it to the board.  The converter passed loopback test so I believe it is a working device.  Also, I believe the proper setting for the converter should be 4 wire mode, however I did try the other modes with no success.  I'm sure the mistake I am making is basic however at this point I am out of ideas since as far as I can tell the right information is being sent throught the port and all of the wiring between the port and device is consistent with rs485, at the very least I would expect this to yield some activity at the boards.  Thanks in advance.

[Scott-M]

Hi RBJ,

You may want to try using NI-Spy to check what exactly your sending on serial ports from NI software, you can use another (non-NI) serial port sniffer (like portmon) to monitor what exactly is being sent on your system that works. Hopefully comparing these output will let you know what your doing differently.

If your device is passing loop back tests, you may also want to try to use them with another device, you may also want to try controlling your boards with the other system you have set up just to double check there is nothing wrong with the boards.

Post back with what you find and we can work from there.

Scott

[rbj]

Thanks Scott,

I tried NI-Spy and that verified I was sending the same strings on both systems.

The good news is after messing around with wires today I was able to figure out that swaping the following wires seems to solve the problem:

RXD- (5) with TXD-(9)

RXD+ (4) with TXD+(8)

I find this to be a little strange since according to the device pinout and the wiring I traced from the boards everything should match, I will experement with this more tommorow and see if I can figure out exactly why these wires need to be swiched.

-Robert

[Scott-M]

Good trouble shooting RBJ, post back if you need any help\find anything interesting.

Scott M