Hello, I am trying communication between a PC and a UDC1000 with RS485 option and Modbus protocol. I am try out the communication using the demo Modbus serial application from Automated solutions. I am facing problems of inconsistent communication viz. some times the error message I get is CRC error or Comm timeout error and occassionally the communication is a success. I look forward for some help with regards to the settings to be made in UDC1000. Thanks & Regards. K.Ramesh Access Automation Pvt. Ltd. Bangalore INDIA

 

I am not sure what the demo modbus serial application is, but here are some things that make the comm link between a UDC1000 and a computer better:
First, don't run it at 9600 bps, unless you have 32 of them in a row, use CbS 1200. Second, use CPAr odd. Also, you need a good rs-232 to rs-485 converter. I would recommend www.bb-elec.com, they make pretty solid converters. On the bench this doesn't make much difference, but if you are going to wire this through a factory, or in an electromagnetically noisy place, you have to use good, shielded wire. Your converter's settings have to match the settings in the UDS (bps, parity, etc). I have three systems, one of 28 units, one of about 12 units, and one of three. The first one gave me the most problems, which I eventually tracked down to a loose shield wire. The noise in the line caused intermittant problems like the one's you described. So, basically, make sure you have CbS set to 1200, CPAr to odd, and have the settings in your converter and software set to match. Make sure you have a good converter with good shielded cable (and the shield is grounded properly!).
Enjoy!
Garrett