MSG Blocks

[Oceansoul]

Im having some issues tracing bits through a message block. The bit originates in a PLC 5/80 (N246:10/0) and is messaged to a SLC 5/02. DH+ from port 1A of the PLC, to a 1785-KA5 Module. This is node 36. Then to the DH485 side and to SLC 5/02 node 7. The issue im having is with the message block set up, and where in the SLC does my data arrive. It says in the MSG block "data table address" 24, but there are only 12 data files in the SLC.

This setup works (to a fashion) but i dont understand

Ive attached some screen shots. (The linx tree shows red X's on SLC500's because i had disconnected when i took the screen shot.

 

[Ken Roach]

The key is the "PLC-2 Unprotected Read" in the MSG instruction dialog box.

The MSG instruction is in the PLC-5 but the data is being Read from the SLC-5/02 and placed into the PLC-5 data table. Your post suggests you intend it to be the other way around.

I suspect that the PLC-2 style message is being used because it will transit these old DH+/DH485 bridge modules.

PLC-2 controllers didn't have numbered data tables; there was one big Data Table that you'd just read and write offsets out of.

To emulate that, the PLC-5 and SLC-500 use a "PLC-2 Compatibility file", also called a Common Interface File or "485CIF".

My recollection is that this is Data File 9 in the SLC-500 controllers. You can switch between "byte mode" and "word mode" using Status bit S:2/8 but I think Word Mode is default.

So performing a PLC-2 Unprotected Read on "Address 12" should read N9:12.

 

[Oceansoul]

Doh. I posted the wrong msg block. There is a write block too.
Many thanks for that info though. I'll have a further look tomorrow