andrew_pj

Dear experts,

I have similar scenario, but I have successfully perform communication using ModSim as Modbus slave. In the Siemens sample program, it is only using function code no 1.

However, my requirement is to use 2 function codes at the same time (no 3 and 16).

So I create multiple database and calling functions which contains function code 3 and 16 in sequence every 2 seconds. This way I can get it works, but not perfect because after some moments, SF red LED on CPU is on.

Please advise the essential solution for using multiple function codes in Siemens PLC.

Thank you very much.

andrew_pj

Dear Navnag,

Thank you for your advice.

Now I am able to read and write without considering time delay.

However, I still got error in SF LED. The error message is as followed:

Event ID: 16# 2522

Area length error when reading

Global DB, byte access, Access address: 13

Requested OB: Programming error OB (OB121)

Priority class: 1

Navnag

Hello

This usually means that the DB that you are trying to read is not of sufficient size. i.e. you are trying to read an address in the DB which does not exist.

Try to increase the size of the DB so that it contains all the addresses that you are trying to access.

Pl check your program , if needed pl post your code here for additional help.

Hope this helps

Cheers

Navnag

Hi

Where should I go to change the size of DB? 

Thanks