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Can Not Establish Communications with SLC 5/04
Cannot establish comm's with SLC 5/04 CPU thru RSLinx.

I have a .pdf with all the pertinent info and a few pictures for clarity but if it is possible to connect to this message I did not see how. The short story is here:

Allen Bradley PLC SLC 5/04
On my laptop I'm running XP Pro SP3
RSLinx Classic Lite 2.59.02
RSLogix 500 6.30.00 (CPR 6)

In use the CPU is setup for comms on:
Channel 1 - DH+ @ 57.6K, Node Address 53 (Octal)
Channel 0 - Driver= DF1, Full Duplex 9600 N,8,1 CRC and the Ch0 USR info is= Driver= ASCII, 1200 N,8,1 No handshaking.

I have 3 cables:
USB-1747-CP3 (USB on one side, Serial connector on the other)
1747-UIC (USB on one side, Serial connector on the other)
HMI-CAB-C49-J (9pin mini-Din? {serial?} to DB-9.

You can reach me via email at and I can forward a .pdf with good pictures of the cables etc. All help is appreciated!


By Bob Peterson on 2 March, 2017 - 2:55 pm
1 out of 1 members thought this post was helpful...

The 1747-UIC is for DH485 which will not work in this case.

The HMI-CAB-C49-J appears to be a GE cable for the quick panel operator interface, so might not work.

The USB to 1747-CP3 is probably the way to go. Figure out what com port the USB com adapter is set to (you can find this out in device manager in windows), then go into rslinx and setup a DF1 driver with that com port. there is a button you can click on that will automatically set your driver up to match your PLC. You should be able to see the PLC in rslinx. You can then open up rslogix 500, goto communications, who active, and select the PLC from the list it will show you for that driver. If you have AB support, it might be easiest to just call them if you have any problems. They are pretty good at getting people hooked up and if you are paying for support you might as well use it.

Thanks Bob,

I was able to reestablish comm with the PLC using the 1747-CP3 cable but I had to reset the CPU card. I suspect that the program changes the protocol on the channel to something that the 1747-CP3 can't handle. Because as soon as I load the program, I get the message about losing comm when the setting are changed from default.

I'm taking the module back to the factory today. I have high hopes of the equipment working again :-)


By Bob Peterson on 3 March, 2017 - 10:04 am

The comm configuration is stored in what gets downloaded to the PLC, so it might be different. After the download just go back to RSLinx and run the auto config again on the DF1 driver and it will find what the correct configuration is.

You can check to see what the comm config is in the program offline before you download it.


You could also try using a serial to USB adapter. It is a lot cheaper than the CP3 adapter and does exactly the same. You'll need a DB9 to DB9 serial cable (which is what the original 1747-CP3 cable is). I know these items are getting scarce, but worth a try. You can contact me at if you need further info.

Best of luck.