ModBus/TCP MSTR Block Example Please


Thread Starter

Len Morgan

We are trying to do our first project using ModBus/TCP and we are having trouble getting out of the starting gate.

We're using Momentum controllers for both the master and slaves. We have set up a MSTR block to request data from a single remote but we never seem to get out of the master.

What I need is an example of what we're supposed to have in our MSTR block. For example, what order do the bytes go in for the IP Address? The manual never says. Should it be 10,6,0,2 or 2,0,6,10 (the IP address of the slave is

Do we need anything in the MAP register (just before the IP address)? We're getting an F001 error in the error status.

We can ping both devices from a third computer so the network is ok and the IP addresses have been programmed correctly.

Any help would be appreciated.

Len Morgan

After a call to Schneider Electric, we got things talking but not until spending an entire day at it. The main "secret" which is not in the documentation is that on the configuration screen, the word just before the IP address, head routing or something like that, needs to be 0100 (Hex) in order for it to use the Ethernet port. If you set it to 0, it is trying to communicate on the ModBusPlus port.

Once it was talking on the right port, the rest of our problems just had to do with timing and making sure that all of our processing was done before the next poll.

Len Morgan