FMD MODBUS Long delay answering

[acxysty]

Dear Tri_PLC
Doing some measurement with a scope we notice that the delay betwteen the request adress to the FMS and its answer is around 40 ms as it can be seen on the joined pic.
This capture show 3 requests adressed to 3 slaves, the FMD being the last one. The 2 first send answer within a few ms while FMD replies in 40 ms.
Any explanation or suggestion to reduce this delay that is well over the MODBUS protocole definition !
Thank you for your help.
Thierry

[support]

Are you communicating with the FMD PLC via RS485?

You can try the SETSYSTEM 3, 0 command as described in the following document:

https://triplc.com/TRiLOGI/Help/tbasic/setsystem.htm

[acxysty]

Thnzk you for your help.
Yes we are using MODBUS RTU / RS485.
We will test the SETSYSTEM(3,0) instruction.

[acxysty]

We tested the setsystem 3, 0 and we still have a long delay before the FMS replies, around close to 35 ms.

The image shows 3 queries on 3 differents slaves : The 1st and 2nd queires give immediate answer while the FMD need close to 35 ms.
Any idea wyhy ?

Regards
Thierry

[support]

Can you try to put the FMD PLC in PAUSE mode (you can turn on DIP switch #4 and reset the program) and then test the Modbus response time again. If the response time is shortened considerably then it is likely because the logic scan time in the PLC program is taking too long.  This can happen if you use a lot of DELAY statements in custom function to achieve time delay.