PLC5 Addressing modes - 1-Slot with 32-Point Card

[kreskin]

Hi All,

I am looking at a future project that includes a PLC5 with some digital I/O.

Its been a long time since I have worked on the PLC5 platform and I am re-familiarising myself with the addressing modes.

Happy in general with the various combinations, but one arrangement that I cant get my head around is when using a 32-point digital Input or Output card in 1-slot addressing mode.

So a group is one Input and one Output word.

Lets say I want to locate a 32-point Input card in physical slot 0.

In one slot mode, as I see it, I only have one Input word (16-bits) available.
So how can I use a 32-point card?

I see how things works in 1/2 slot mode as the two groups in the one physical slot provide two input words (32 bit), but cannot see how this is achieved in one slot mode.

Any help would be much appreciated.

 

[OkiePC]

It's been a long long time, but I think with that setup, the 32 bit card will use two input words but you must not have an input module in the next higher slot...you have to alternate the cards input, output, input, output, etc.

So in your example, the first 16 inputs would be addressed as I:0/0 through I:0/15 and the last 16 inputs of the card in physical slot zero would be addressed as I:1/0 through I:1/15

I'll see what the Rockwell knowledgebase has to say to see if my memory above is correct.

EDIT:
https://rockwellautomation.custhelp.com/app/answers/answer_view/a_id/46412/loc/en_US

 

[Operaghost]

Yeah, 32-point cards were designed with 1/2-slot addressing in mind. Getting it working with 1-slot requires a few things. For this example we will assume that the I/O modules are in slots starting with 0.

First, when you put your input module in (physical) slot 0 it will use all 16 input bits (aka word or I/O Group) assigned to that slot. Then it will go to the next slot and borrow all 16 input bits assigned to that slot as well. Now slot 1 does not have any inputs available in memory so you cannot put another input module in that slot. Whatever module you place in the first slot, you would place it's complement in the next slot. In slot 1 you can now place a 32-point output module. The first 16 outputs will come from slot #0 and the second 16 will come from slot 1. The modules will only borrow in even odd pairs. So slots 0/1, 2/3...etc. Slot 1 will never borrow from slot 2. Of course, this requires you to alternate input and output module. When you move to slot #2 you can place either an input or an output in that slot since it is a new slot pair. Then slot #4 would need the complement to slot #3. For example, this would be valid for slots 0-3:

In(0) Out(1) In(2) Out(3) or
In(0) Out(1) Out(2) In(3)

Slots 0 and 1 will only borrow from each other, and Slots 2 and 3 will only borrow from each other.

This would not be valid:

In(0) In(1) Out(2) Out(3)

Using 32-points modules with one slot addressing really requires a fairly balanced number of inputs and outputs because of that whole alternating module thing. If I had a bunch more inputs than outputs then I would have to skip slots. For example:

In(0) Out(1) In(2) Empty(3), In(4) Empty(5), In(6) Empty(7), In(8)

If you have a lot more inputs than outputs, then 1/2-slot addressing is a better option as each half-slot is assigned a word of input and output memory. Or, read that another way, and each slot is assigned two words of input and output data. This allows you to place the 32-point modules in any order you like.

The benefit of course to complementary I/O is that you fully utilize all of the I/O memory that is available. If you look at the specs for the PLC-5 they actually expect you to NOT complement the I/O. So if they say that your CPU can handle a mix of up to 1024 I/O, it can actually handle 1024 inputs AND 1024 outputs. But it requires you to complement all of the I/O, which isn't usually feasible.

Hope that helps a little (Okie typed faster than I did). I got to dust off my PLC-5 instructor chops

OG

 

[OkiePC]

Hope that helps a little (Okie typed faster than I did). I got to dust off my PLC-5 instructor chops

OG

Yeah, but your explanation is much more thorough and detailed. Glad a real expert chimed in.

 

[kreskin]

OperaGhost, Okie,

Many thanks for the quick and concise response to my question.
I was not aware that the memory was actually borrowed from the opposite slot in the pair, so this now all makes complete sense.

Much appreciated