Posted ByLuc Bastien on January 24, 2002 at 12:43:55:
In Reply to: Re: Modicon Momentum communication problem posted byLeon on January 11, 2002 at 03:12:44:
: I have seen a problem close to this one in the past and discovered quite a bit on the communication setup with these type of boxes. Your problem maybe the way you have setup the termination and/or wired your rs485 loop. Send me a schematic of the installation and I will take a look.
: Our PLC may be able to speak and answer to MODBUS command, but since we don't make the Modicon PLC I can't say for sure what was the problem. But if you are getting response from the PLC, the communication link seems to be fine. If the Modicon PLC acts as modbus slave it will only respond to command from the PC. You probably have to find out which internal address the input is being connected to and send the modbus read command 03 or 04 with the correct address accordingly. I hope other Modicon user can offer you some help.
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: : I am using a Momentum 1760 00 style processor and i am trying to use a PC to communicate to PLC on Modbus port 1. The PC is 205 feet from the plc so I bought a B&B rs232/485 converter for both ends (PC & PLC) I have a Null modem connected at the PLC side and a standard RS-232 9pin to 25 pin cable at the PC side. I am able to read data from the PLC but I can not send any commands down to the PLC from the PC. Using ProworxNxt I get an error message that states I am not logged on to the PLC, Using LOOKOUT software I see the values update dynamically but if I turn a switch on/off it does not get sent to the PLC.