I am using a desktop computer com 1 port to communicate to a GE-Fanuc 90-30 PLC. We are also using the same com port to communicate with a Automation Direct-EZ Touch Operator Interface. These are being used in a classroom setting and causes students to have to switch cables on a regular basis. Is there a device that will allow the connection of the devices without having to change the cables? Allen Bradley has such a device (AIC).

Dolph

 

A simple A/B switch will work admirably and they can be quite reasonable if purchased from the right place, especially in quantity. Try computergeeks and some of the other computer surplus outfits. With the duopoly trying to
stamp out good ol serial ports, switch boxes should be cheap.

Regards

cww

 

You won't want something that leaves them both electrically connected to the same ccm port because they don't use the same comms protocol, but you can just use a serial port switch with a rotary selector. You will provide a serial extension cable from your COM1 to the switch box, and the normal programming cables from the box to the PLC and MMI. Then the student can select without changing cables.

A better solution is to keep both electrically connected at the same time to different com ports. Your desktops probably have two serial ports; if not you can add one. I know the EZ Touch software doesn't mind if you use a USB to serial convertor. I don't know about SNP; I've never tried to use it with a USB serial port. Then the students can switch back and forth between the PLC and MMI, much like the way it's done in real life. This will be expecially valuable in your case since you're using the EZ
Touch, one of the few MMI's that allows run time edits. So you can create a button, send it to the MMI, press it, and see the bit go true in the PLC data register, all in about 60 seconds from start to finish. Pretty cool. Troubleshooting of MMI/PLC issues is also easier if you are online with both at the same time.
--
Steve Myres, PE
Automation Solutions
(480) 813-1145

 

I have one on my desk here - a serial A-B switch in a steel box with a knob on the front for the choice of either A or B. The back of the box has 3 serial connectors (DB9F).

The one in the middle is labeled input/output and is the "Common", the other 2 are labeled A and B respectively.

When the switch is in the A position, input/output is routed to A.

When the switch is in the B position, input/output is routed to B.

Cyberguys used to carry the serial A-B switch, but has dropped it. Now the only choice is the 4 to 1 VGA, keyboard, mouse switch (ABCD) # 105 0192, which should work Ok, just leave the DB15 or round connectors empty.

You might have to get some of those thin-profile gender changers, DB9F M-M, to adapt your serial cables to the DB9F connectors, but they're inexpensive at Cyberguys.com: # 130 0300