STATUS(2) and MODBUS

[ccdubs]

Hi All,

I am having difficulty with the status(2) command. I am using the writemb2 (RTU) command to send data to a PC. The PC receives the data correctly but it seems that the PLC is not sending STATUS(2) = 1.

Is is possible that the PC receives the datagram but the PLC thinks there was a transmission fault?

Thanks

[support]

Does your PC respond with the correct MODBUS Response? What program are you running on the PC? Can you show the MODBUS command that you are sending? How many data are you sending in a single WRITEMB2?

[ccdubs]

Hi Support,

It turns out that the problem was with the communications medium, radio. If I connect directly to the PC the communication was good.

I have found a workaround to this using the PC and PLC as modbus masters and slaves so that I can then check data was received using two way communications.

Thanks.

[support]

I think the radio latency is what caused the problem. The response from the PC takes longer than 0.15s to be returned to the PLC and therefore the command is considered to have failed. There is a SETSYSTEM command that can change the amount of time that the PLC wait for a response from the slave.

Look into your folder:

C:\TRiLOGI\TL6\public\Help\tbasic\setsystem.htm

for explanation of these commands.