communicating with a plc

Hi Team,
We have a slc 500/04 allen bradley plc and I wanted to look at the ladder logic that is written on the program. I have a laptop computer with rslogix 500 software and rs linx communication software. The rs232 light was on the plc so I thought I should use the 232 cable to hook to the laptop. The laptop does not allready have a file of the program so I thought I could copy it once I communicated to the plc. I kept getting a communication error that said " device node not found ". The old siemens 405's had to have a program on the laptop. Does this hold true with A/B too? I'm missing the boat on the communications.
Please if you can help it would be very appreciated..

Thanks for your help...

Close, maybe!

Well, you do not have to have the PLC program resident in your laptop to upload or even go online with the program stored in the PLC memory. You do however have to have a properly constructed nullmodem cable, configured serial (DF1) comms in RSLinx and then you should be able to establish comms with the processor and proceed from there. You could also use the USB to DH-485 cable to communicate but AB wants around $200 bucks for that darn thing and the nullmodem cable you can make yourself for under $15.

In addition to the right cable, you need to have RSLinx setup correctly to communicate with the processor.

If the processor is setup for rs232, then open RSLinx,
navigate these options Communications->Configure drivers
If DF1 serial driver is not present, then add it.
Next, open the properties for that driver, attach your cable and hit the auto-configure button. This should automatically set up the baud rate and other settings that you need to get online.

If you're unable to communicate with the processor after doing this then your problem is probably:
A) Bad cable/hardware
B) the processor is actually setup for DH485

Option B is the easiest to check for and still get online with the same hardware.
To do this, delete the DF1 serial driver from the list of installed drivers under RSLinx. Then, add a PIC driver. Depending on the Operating system, you may need to restart Lynx to get the pic driver to add. The PIC driver doesn't have an autoconfigure, but it probably won't need any changes from defaults.

jimbo3123 said:

Next, open the properties for that driver, attach your cable and hit the auto-configure button. This should automatically set up the baud rate and other settings that you need to get online.

Click to expand...

Just make sure you have the correct comm port and processor type selected first. COM1 is ASSumed but you never know...

I've noticed that the first time I try to go online with some PLC's I have the same communication problems. I've found that using the "Go Online", or "Upload" Command from drop down menu on the RS Logix Main Screen usually doesn't work for me the first time. I suggest after properly configuring your drivers and cables as explained in the previous post's, when going online or attempting an upload, navigate in RS logix to (Comms, System Comms...) then highlight (click) the PLC icon in which you want to communicate with. Then use the Upload or Online button to start the Communications. If everything is properly configured you shouldn't have any problems.