Author Topic: RS485 sometimes not working well  (Read 2028 times)


  • Newbie
  • *
  • Posts: 5
    • View Profile
RS485 sometimes not working well
« on: June 07, 2020, 09:52:53 AM »
I working with fmd1616 i try communicate with other controller Rs485 com3 , 8,n,1 baud=115200

Sometime the slave controller not respond for readmodbus command and sometimes yes.

When i working with computer and usb to 485 - the slave controller respond for all commands.

What can be the problem?


  • Global Moderator
  • Hero Member
  • *****
  • Posts: 3128
    • View Profile
    • Internet Programmable PLCs
Re: RS485 sometimes not working well
« Reply #1 on: June 08, 2020, 02:18:40 PM »
What are the other controllers? Are they third party controller?

Do you know if the actual baud rate of those controllers?  Most controllers that advertise 115200 don't actually communicate at that precise baud rate but a close approximation (up to +/-3% of the target baud rate). So is the Fx PLC.  The closest baud rate that Fx PLC support is  117200 which allows it to communicate well with a PC at precisely 115200 bps. But if the other controllers actual baud rate is lower than 115200 then it is likely that the actual baud rate difference is larger than +/-3 %, which can lead to more errors.

Try to communicate at a lower baud rate if the highest baud rate don't work well.
Tel: 1-877-TRI-PLCS