Modbus Stalling

I have an issue with the program I have written. I have a Horner Micro OCS 7 connecting to a Fanuc robot via modbus. When I am running it I see the modbus communication on the robot run just fine. It has started stalling out at the same point. When the Cycle_Start(line 20 rung 14 in the program) signal is sent to the robot it appears that all communication stalls out. I have a heartbeat signal set up on line 22 rung 16. While it is running normally I see that heartbeat signal but when it goes to send this cycle_start signal that stalls out as well.

Sometimes it will come back to life and send the signal. This problem started out where this would happen once in a while and it would come back to life and keep communicating. This problem has become ever more or an issue.

Any hints or help would be great. I have seen some links to modbus sniffers but I am not the most well versed in modbus comms. I followed a set of instructions written for setting up these comms.

Can you elaborate more on the comm path? Modbus serial (RS232 or 485)? Modbus TCP? which is the master and which is the slave. I'm not too interested in the programming part if it worked before. Sounds more like a physical layer issue.

harryting said:

Can you elaborate more on the comm path? Modbus serial (RS232 or 485)? Modbus TCP? which is the master and which is the slave. I'm not too interested in the programming part if it worked before. Sounds more like a physical layer issue.

Click to expand...

The plc is the master and the robot is the slave.
I am communicating through ethernet network connection.

the protocol it is using is Modbus Tcp/Ip client v 1.08.

Ok, I guess at this point you will need to find out if it's the master side or the slave. one thing I always check is to just do a continuous ping to both master and slave and see if there are any gaps. Any gap would point to a general network issue not necessarily Modbus related.

If pings are good then move on to use one of the many modbus slave/master simulator to see if you see inquiry from master and response from slave.

harryting said:

Ok, I guess at this point you will need to find out if it's the master side or the slave. one thing I always check is to just do a continuous ping to both master and slave and see if there are any gaps. Any gap would point to a general network issue not necessarily Modbus related.

If pings are good then move on to use one of the many modbus slave/master simulator to see if you see inquiry from master and response from slave.

Click to expand...

I will do that. It's odd that it will run fine through the rest of the communication including the heartbeat signal I have that also stops right when the stall happens at the exact same spot in the process.