cx-protocol disapointment again

[pro17 0]

This is strainge. I wrote Modbus/RTU messages I use to communicate with some equipment (5 devices). This is the way I prepaired messages: 1) Send messages 2) Receive messages 3) Modbus sequence / steps 4) Protocol 5) Tracing messages!!! - look at error description in a picture As you can see, step 13 isn't executed at all. It looks like PLC isn't even trying to send the step13 message! Also step12 message gets returned as it should, but the data isn't written into DM area as it should! Other steps works, also data is written into DM area. Any suggestions? JinX

[pro17 0]

Found a problem. In recieve messages there are some limitations on writing message data through Message Variable. Variable 261 and 271 were to big. Changed them and now it works OK, also step13 is working. JinX Edited 10 Nov 2008 by pro17

[Sleepy Wombat 27]

Thanks for the feed back on the problem you had...

[lchamarthi 2]

Hello All, From this thread I understand, You guys are strong in playing with protocol messages. I am just learning Modbus communication with PLC using PMCR and readily given modbus macro from this Forum. I was not able to really understand from manual about the Data variables defined in sent message list and receive message list. I am using Function code 3 for read and 8 for write in protocol macro downloaded from forum Data field example – what does this code mean? <a>+SOH+(R(2),4)+<c> Please help me in understanding of this........ Thanks

[pro17 0]

First you need to learn Modbus message format. Learn here: http://www.lammertbies.nl/comm/info/modbus.html For send and receive messages look at my first post. This messages are correct for doing Modbus RTU communication. Also, you donwloaded PMCR code and CX-P code. This does work as it should. Edited 14 Nov 2008 by pro17