Modbus RTU Communication problem


Thread Starter

Sam Lee

I am using PanelMate (from Cutler-Hammar)to communicate with ACM (Siemens-Moore's product) through Modbus RTU protocol.In this application,PanelMate acts master while ACM slave. I can have some communication. but some signal can indicate in the panelmate some can not. and when I try to write a bit to one address,two different address got a reading.PanelMate always got an error:Loc:1702 on plc1 via port2 reading 00193,00593. Actually I did not specify 00193 00593 at all.TIC of Cutler-Hammar confirm the configuration in panelmate to work well in Modicon PLC. From Moore's side the communication is good. Anyone have the successful experience of establishing communication between ACM and PanelMate through Modbus RTU?Any good suggestions? Thanks Sam Lee Tel:001-403-298-7570 E-mail:[email protected]
One suggestion - if you're using RS-232, maybe your cable is not wired correctly. Contrary to popular myth that "any" data comm means the cable is correct, since RS-232 is so sensitive to capacitance it's possible to have even 99% correct data comm with the TX is tied to TX & the RX to RX is floating. I've seen this in cheap, very-thin cables as short as 10 feet and of course in the long cables like 30m or more this the "normal" behavior when you don't cross when you should. At another site with 30m cables, only the FIRST char of each page on a printer was garbage - otherwise the print-out was 100% good. This problem lasted for nearly 2 months until I opened the cable (customer swore up & down they double-checked it 3 times) and saw that it did NOT have the null-modem like loop-backs that their cable drawing said would be there. It was a straight-thru cable when it should have been crossed. See the app note at on how to use a volt meter to confirm your cable. It'll take just a minute to verify absolutely. Regards Lynn August Linse, Senior Product Application Engineer 15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618 [email protected] Tel: (949)300-6337 Fax: (949)453-7132