1784-PKTX communication problem

[rajsiyer 7]

Hi guys; How I wish someone like Ron Beaufort was around....You see.. I'm having a problem of intermittent communication with the 1784-PKTX card, attached to the PC as shown in the diagram. In Rs-Linx's RS-Who? window I can see only 5 out of the 8 Plcs on the DH-485 net, that too with the Red-Cross (disconnected status ) circulating round-robin style among them. There are even brief moments when 5 PLCs all appear connected on line. But for most of the time, 2-3 plcs have disconnection and then they re-connect. At times, all appear disconnected for a few seconds after which a few re-connect. On the PC, the OS is Windows-XP and the In-Touch version is 9.5. Earlier there was In-Touch version 7.0 installed on Win-98. AT that time, it was possible to see 7 out of 8 PLCs communicating. Initially, with win-98 & Intouch 7.0, it was possible to up-load the RS-LOGIX programs from the & communicating PLCs. This is something no longer possible.(Baudrate =9600, Parity - odd, stop-bits =1, data bits =8, for RS-Linx and all PLCs on the DH-485 net). The total length of the DH-485 cable will be around 200-250 metres.No termination resistor has been provided, at any 1761-NetAIC coupler or at the end of the bus. A million thanks to the guy who can help out with advise.Surely a lot of beer should we ever meet. Raj S. Iyer PKTX_prob.doc Edited 7 Jun 2006 by rajsiyer

[gravitar 3]

I haven't looked at your diagram but from your description, it sounds like you have a classic wiring/termination problem. The standard rules for DH485 are: Grounded at one end, terminated at both. (Note that the termination resistor is built-in to the AIC and you just have to tie into the termination pin) Unique node number for every node Same baud rate and max polled node number for all nodes. Daisy-chained topology, NOT star. I'll bet if you check the above parameters you'll be able to see all your nodes!

[rajsiyer 7]

Attaboy gravitar!! Wilco. Shall try it now itself. Thanks for your prompt reply. And man I'd like to see you winning that bet! Regards, best wishes for a happy day Raj S. Iyer