AB quick reminder for addressing

Hi guys,

Just quick reminder. With SLC 500 series PLC's addressing for a remote rack. I know for a local rack is goes something like this:

I:0/1 for Slot 0 bit 1. Just for example.

What about it was located in rack 2, slot 3, bit 4?

I:2:3/4. is that right? Something looks wrong to me and I can't remember how it goes.

Can you help me out?

With a SLC, your remote rack(s) will be connected to a scanner card in the local rack. The scanner can handle up to 32 words of input data and 32 words of output data or four logical racks. The first logical rack (rack 0) will be the first 8 words of input data and first 8 words output data assigned to that scanner card. (If configured as a full rack.) The second logical rack will be the next 8 words, and so on. The addressing syntax for an input will be:

I:<local_slot>.<logical_rack>/<bit>

local_slot is the slot number in the local chassis that contains the 1747-SN RIO scanner card.

Now, it can be complicated depending on how the G file for the scanner is set up. It is possible to begin a physical rack at any even word within a logical rack. Most of the time it isn't done that way. Ususally, rack 0 begins at word 0, rack 1 begins at word 8, rack 2 begins at word 16 and rack 3 begins at word 24. Now, let's assume (<- dangerous word!) that your system uses this common sense way of addressing racks and that the scanner in the local rack (with the SLC processor) is in slot 3.

What about it was located in rack 2, slot 3, bit 4?

Click to expand...

If the scanner is in local slot 3, the address for your example above would be:

I:3.19/4

The "19" comes from 16+3 where word 16 is the start of logical rack 2, and 3 is the fourth (slot 0 counts!) slot in that rack.

Still confused?

Read this

Paul C.

sirhiss2
When you say "remote" do you mean a chassis connected via a scanner card (which is the "correct" meaning)or do you mean a chassis connected by ribbon cable?

If you are connected with the ribbon cable (chassis extender, not a true remote IO rack) then you just keep counting from where you left off.

For example with two 10 slot racks connected by a ribbon cable, the first discrete input in the second rack is I:10.0/0.