RS232 cable

[jblkiller]

I have a M91 into a box. I would like to have a acces to the RS232 port for troubleshooting whithout open the box. I connect the cable to a coupler like that: (http://www.digikey.ca/product-search/en?x=0&y=0〈=en&site=ca&KeyWords=a34359-nd) but the plc don't want communicate. I check the continuity for both cables and is ok. I there a maximum length for rs232? When I plug the plc direct to the pc with one cable is ok. When I connect two cable with the coupler don't work.

Thanks

 

[Flex727]

The typical RJ-11 cable (like used for phones and like what comes with the PLC) is a crossover cable. If you add an additional cable between the PLC and the coupler it must be a straight-thru cable like this one:

http://www.monoprice.com/Product?c_id=102&cp_id=10222&cs_id=1022201&p_id=928&seq=1&format=2

 

You are probably doing a double crossover which will not work. Two crossover cables WILL only work if the coupler is also a crossover.

 

Where I work we do exactly what you are trying to do and encountered the same issue you are having. A straight-thru cable inside the box works perfectly.

[jblkiller]

Thanks you for the explanation!