NI Max Visa Test Panel modbus communications problem.

[Surgeboard2012]

I am trying to communicate with an Automation Direct Direct Logic 405 D4-450 plc processor.  I am using NI Max VISA Test Panel.  I keep getting a timeout error when I try to send commands.  I found that I can send a "Coil 2064" to the plc and I should get a response from the plc telling me the status of the output Y20.  I have tried other commands that was in the Automation Direct manual for modbus communications but no matter what I send I get the same timeout error.  I noticed that I get the same timeout error with the plc connected or disconnected.  So I am not communicating with it at all.  I have both the NI Max and the PLC settings the same.  I was wondering if anyone has done something like this with any success or if anyone knows what I should try.

[Jeff-P]

Hi,

Since you are not able to communicate at all -

Does the COM port show up in MAX? I assume it does if you are sending it commands. If it shows up in MAX, try sending it an IDN command (*IDN?) and monitor for a reply to see if that communicates with the device. If the port is not in MAX, check in device manager to see if the port shows up and make sure that your NI-Serial driver is the latest version.

You can also try a serial loopback test. If the serial loopback fails, try using a different cable or connecting the device to a different machine to isolate the source of the problem.

Regards,

[Surgeboard2012]

I have talked to Tech Support and they told me that I will not be able to use NI Max to communicate with the plc but that I can use Labview to communicate with it.  I am waiting to hear back from Tech Support on how to communicate with the plc in Labview.  I have tried using the MB Serial Example Modbus.vi to communicate with it but I have not had any luck.  Does anyone know how to use that vi or do you know of another vi I can use?  The command that I need to send to read an output in the plc is "Coil 2064"  or "Coil 2065".  That will give me back the current status of output Y20.