PLC-2 to PLC-5 with a 1771-KG Modem Card

[Andy6]

Hi guys,

I have a PLC-2 system with a bad processor. I've done all the changes to get it up and running with a PLC-5 processor. The only thing I'm not too sure about is that the system uses a 1771-KG modem card to talk to a AB keypad interface. Any chance of this working? It looks like the modem can talk the same language as the newer PLC-5, but of course the manuals make no mention it.

Thanks

 

[JaxGTO]

The KG uses the Data Highway protocol which is an older form of the DF1/Data Highway Plus protocols. You could write code in the PLC5 to emulate it. I did it a long time ago using Quick Basic so it's not to complicated. Just download a Data Highway book from AB.com. Your Keypad interface will be trying to access PLC 2 data table words, so you would have to have the PLC5 emulate receiving those packets and putting the data into PLC5 type table. I don't know if the Keypad interface can switch to using PLC5/Data Highway Plus protocols.

 

[Ken Roach]

It might be as simple as defining a PLC-2 compatibility file in the PLC-5 controller.

That would make your selected integer data file (like N9:0, for example) respond to read and write commands that are addressed using PLC-2 unprotected read and write command codes and PLC-2 data table offset values.

Do you have a PLC-5 with a Channel 0 RS-232 port ?

I don't have RSLogix 5 loaded on my PC anymore, and I'm having trouble finding in the reference manuals how you designate which PLC-5 data table runs as the PLC-2 common interface file. Maybe it's always Data File 9, like on the SLC-500.

 

[Andy6]

Thanks for the information guys.

Ken, I do have the channel 0 port. I have a new cable installed between the PLC and the modem, and the Processor led on the modem (comms) is flashing, which is really nice to see. So I think they are talking.

I'll see what I can dig up about building a PLC2 compatibility file for PLC5.

Thanks again!

 

[Mike_RH]

I recall that the PLC-2 compatibility file for PLC-5's depends on the source station number.
As an example: if the source station number is octal 20 (decimal 16), then the PLC-2 compatibility file would have to be file 16. The data type could be any type where the element is 1 word, so binary/integer/BCD would do. The file has to be large enough to include the PLC-2 (octal) address.

 

[Ken Roach]

Mike, I think you're right.

I think that's how it worked with PLC-3 controllers as well.

Andy, if you can capture the serial data polls coming from the modem with RealTerm or Docklight or another serial "sniffer" we might be able to decode them and figure out the addressing.

This is probably a very good opportunity to plan a replacement for that keypad module; it's probably from 1978-1984 or so and can't run forever.