READ_VAR and WRITE_VAR limitations

[GO0DY22]

Hi,

I have M580 CPU and i would like to communicate with other Modbus TCP devices using the CPU ethernet port. I'm using the READ_VAR and WRITE_VAR blocks but i have some intermittent timeouts. I would like to know the limitations of thoses blocks (read and write) ? I do many READ_VAR and WRITE_VAR at the same time(maximum of 10). I'm using the EN input on the read_var /WRITE_VAR with %S6 and a NF contact with the activity bit. How many READ_VAR/WRITE_VAR should i do at same time?

Thank you,

Fred

[Mnabil]

Hello Crewman,

actually, I do not recommend using read_Var with a large scale or near the limit, you can use DTM approach  to make suitable communication and you will have 63 connections,

but you can use enable input but Pulse approach will not be effective, you need to create a block to manage the communication and request  queue

[GO0DY22]

Thanks for the answer.

Do you know the exact limitations of the read_var and write_var? I have some request by modbus RTU and i can't use the DTM approach. i have a mix of RTU and TCP modbus devices.

Thanks,

Fred

[Mnabil]

Hello Fred,

You can find the info on the limitation of blocks and DTM on the attached manual as the below print screen