Allen Bradley 1756-L1 can´t go online

[danidangv 0]

I'm new arround here so first of all greetings to all and apologies for my English. I tell you the case: I have a machine that has an Allen Bradley PLC 1756-L1 (yes, it's already a bit old) communicating with another plc, a B&R 2003, through the serial port. I wanted to download the program from AB. I open RS-Linx, I create a DF-1 driver and then click on autoconfigure. At this point I get an error saying RS-Linx can't find the communication parameters. I tried to connect with two other cpus 1756-L1 that I have (these are new so they don't have program) and the RS-Linx locates them perfectly. I guess the ab cpu has its serial port configured as USER to communicate with the B&R plc (or something similar), so my question is if there is a way to connect to this cpu through the serial port (such as putting the serial port in default mode without deleting the program) or the only option left is to find an ethernet card to connect to the cpu. Thank you very much for any answer because I've searched a lot and I don't find any information about this.

[jstolaruk 9]

I believe you are right. You should be able to use one of those other CPUs in a open rack slot to get across the backplane too.

[Ken Roach 194]

I agree with your conclusion that the serial port is configured for USER mode. The 1756 series controllers do not have a "default comms" function because they are commonly connected to over the backplane port. An Ethernet card would be ideal, but another CPU with a serial port will allow (as jstolaruk said) allow you to browse the backplane and connect to the 1756-L1 to perform a program upload.

[danidangv 0]

Today I could try what you have said. I have mounted one of the new cpus on the backplane and through its serial port I have been able to connect to the cpu that had the program and upload it. Once I downloaded the program I have found that the serial port was configured as User mode, for ASCII protocol, making it impossible to communicate with the plc once you download the program and the plc starts running. Fixed issue. Thank you very much to you both for your answers. They have been very helpful. Regards.

[Ken Roach 194]

Thank you for posting the follow-up !