Serial Communication with M251

[Sham]

Hi all,

I m trying to read several registers using serial line(rs485) in m251 plc. I want to know the limitations, as I m facing serious issues of inconsistency. I m using Read_Vars for this, and i m using around 11 of those. Apparently not more than 8 can be active at once, so i have sequenced them, but still i often get error message of 255 (communication error) and 1 (oper error). The registers i m using are not in sequence, so I can’t just use one Read Var block, and the huge number of read vars I believe is causing inconsistencies.
Any suggestions? Any similar experiences ? Any solution?

Thanks

 

[Lare]

Hi all,

I m trying to read several registers using serial line(rs485) in m251 plc. I want to know the limitations, as I m facing serious issues of inconsistency. I m using Read_Vars for this, and i m using around 11 of those. Apparently not more than 8 can be active at once, so i have sequenced them, but still i often get error message of 255 (communication error) and 1 (oper error). The registers i m using are not in sequence, so I can’t just use one Read Var block, and the huge number of read vars I believe is causing inconsistencies.
Any suggestions? Any similar experiences ? Any solution?

Thanks

No, RS485 Modbus RTU is multipoint for several slaves, but for one slave you need to sequence all communication, otherwise you have collision on traffic and lot of errors.