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Communication problem between a PC and a SLC 5/03
cannot establish communication between a PC connected and PLC linked through a RS232 port after downloading the program.

I am working on a SLC 5/03 processor that lost its program.I downloaded to the Allen Bradley SLC 5/03 through the RS232 connector the backup program. The downloading was done successfully and the PLC indicating running now.A PC being used for graphics is connected to the PLC through the RS232 port. A provision was also made for connecting the programming terminal to the PLC through DH485 port (RJ45 Connector).The PC is still indicating fault while the PLC is running. This I believe can be attributed to the fact that I had the program downloaded through the RS232 port using AB-DF1-1 driver while the driver in the initial program backup is AB_PIC_1.Anytime I try downloading the backup program to the PLC, the information below is shown to which I affirm in the negative:Current Project Settings do not match system settings.Current Driver – AB_PIC_1 Driver Selected – AB_DF1_1Current Node – (1Dec)  Node Selected – (1 Dec) Would you like to replace project settings with new settings?Checking the downloaded program online then show that the driver is AB_DF1_1 different from AB_PIC_1 as in the original program.I have a 1747-PIC which could be used to communicate with the PLC through the RJ port but unfortunately the PC connector end is 25 pin female which cannot fit to my laptop.This is the situation I have at hand. Can somebody help? It will definitely be most appreciated.

By Trevor Ousey on 29 August, 2008 - 5:02 pm

Not sure which software you are using, if you are using RSLogix 500 and RSLinx then be sure that RSLinx connects to the SLC5/03 okay. You should be able to see this in Who (part of RSLinx).

In RSLogix, go to who active, browse to the SLC5/03, then 'tick' the 'Apply to Project' checkbox. Then okay. If the program in the PLC is okay, save it.

The 1747-PIC uses a 25-pin serial connection, so just get a 25 to 9 pin adapter and all will work. If you only have a USB then you could try a USB to Serial adapter, which may or may not work. If you have later software, you may have to change RSLinx from being a service.


Thanks Trevor,

I eventually used another laptop with an onboard serial port with a 25 pin to 9 pin adapter to connect to both the PIC and the laptop. I got the driver installed after running RSLinx in application mode. Still, I am not able to communicate with the PLC though I could see the workstation (my laptop). Can you help me any further?




Why not just change the connector on the cable you have to suit your laptop? Are you also updating the HMI software, if so you have 2 connections from your laptop to the PC for downloading the graphics, etc. From the PC to the PLC (Target). The PC needs to switch to the target connection when it starts RSView. It took me a while to figure that out.

Hope this helps.


By Trevor Ousey on 11 October, 2008 - 8:31 am

Hi Adekunle,
Sorry, I forgot to mention that RSLinx needs to be running as an
application. If you are able to use the serial port on the SLC, you can check the DH485 port setting on the PLC. Then you can set the PIC settings easily.

With the RJ45 plugged into the SLC, did the DH485 led show activity?

Let us know how things go.


I think, the problem in baud rate setting or communication protocol in channel configuration is wrong assigned during downloading.

If you remembered that after the downloading completion a dialog box appeared, the buttons of that window are Apply and Don't Apply, then you clicked on Apply button, after this action you lost the communication.

If your problem is not resolved, contact with me. Probably, I would be able to solve your problem.


We had this similar problem , when using a usb to serial converter. Firstly when the usb cable is plugged in you need to note the port it is configured to. then run the rslinkprogram to connect and the run rslogix program.

hope this help