SCU41-V1 RS485 2-wire

[manowar 2]

Hello. I have connected two PLC-s. PLC1 and PLC2. PLC1 is master. It is sending questions using FINS commands. If I use 4-wire RS485 communication ewerything works great. PLC1 sends question and PLC2 answer. BUT problem is if I use 2-wire RS485 comunication. In that case PLC1 send question and PLC2 answer. But PLC2 is answering until PLC1 send another question. It seems like PLC2 is in a kind of loop..... Any ideas? Have a nice day..

[PMCR 66]

Much more information needed. What are the models of the PLCS? I assume CJ1 or CS1. What Protocol is being used? (Host Link, CV Mode Host Link etc). What ladder instructions are sending the data? (TXDU, CMND, PMCR, etc) What are the port settings on the SCU cards? In general, RS485 (2 wire) is a half duplex communication system, so only one device can send at a time. RS422 is a full duplex system, where both devices can send data at the same time. This does not explain why you get into a loop. Edited 13 May 2008 by PMCR

[scottmurphy 1]

As what PMCR says, what PLC's are you using? There could be better implementations of what you are trying to achieve, there are Omron built in methods for doing what you want. If you give more information, then more educated help can be given.

[manowar 2]

What are the models of the PLCS? I assume CJ1 or CS1. What Protocol is being used? (Host Link, CV Mode Host Link etc). What ladder instructions are sending the data? (TXDU, CMND, PMCR, etc) What are the port settings on the SCU cards? Hello. PLC's: CJ1M-CPU11 + SCU41-V1 (on both sides) Protocol: HostLink FINS Ladder instructions: PMCR Port settings See picture. I had the same problem before (while I was testing) but then I use CJ1W-CIF11 and it worked OK. Even if I use 2-wire link. I remember that I enabled RTS signal. But if I use PMCR the RTS signal is driven from PMCR instruction. I'm looking at ligts on SCU (send / recieve): Master sends question (Send Blink) Slave(Recieve Blinks) Slave responds (Send & Recieve Ligts up) Master recieves (Recieve Ligts) It is sending answer until master sends another question. Any Ideas? I have attached test project for master/slave communication (zip file). FINS_Comm.zip

[manowar 2]

Hello. Just info... In ladder diagram there is selected unit=1 but in slave setting there is unit nr.=2 This was leftover from testing. So THIS IS NOT A PROBLEM.. Thank's Have a ice day.

[PMCR 66]

I have tried in 2 wire mode also, and I cannot get it to work. Can you use the 4 wire method for the application?

[manowar 2]

Unfortunately not. Don't misunderstand me... The link works for me, the problem is, (as I wrote before) that SLAVE unit sends answer continuously until the master sends another question. With 4-wire mode everything works fine (one question -> one answer). Bye.

[PdL 71]

Just to be sure; port switch is on 4 wire ?

[manowar 2]

Off course...... On 2-wire is set on 2-wire on 4-wire switch is set on 4-wire.......

[PdL 71]

As I said; just to be sure