Programming

parag uike

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Join Date
Oct 2005
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mumbai
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Hi This Is Parag Here Again,

Plz Try To Tell Me The Programming In Terms Of Rack, Group & Slot Technique Of Ab Plcs.


Thanks In Advance.
Parag Uike
The Game Of Plc+
 
The general convention is I for inputs and O for slot, followed by the slot number and the channel number. Examples are I:2.0/0 and O:3.0/4

The details vary with PLC l, I/O card model, and discrete and analog I/O. You really need to look at the manual for your specific hardware.
 
Rack, Group, Bit addressing refers to the PLC5 family of processors. It is a logical address, not a physical address. Exactly which physical address corresponds to a logcial address will depend on how the rack is configured. Do not confuse the terms "Rack" and "Chassis," and do not confuse the terms "Slot" and "Group."

In the PLC5 you can use 1/2 slot, slot, or 2 slot addressing. A slot refers to a physical slot into which you slide an IO card in the chassis. The slot is not a part of the address. Unlike the SLC and CLX, the PLC5 has a pre-allocated input and output image table. PLC Racks, Groups, Bits are addressed using octal numbers. (0-7, 10-17, etc.)

Group:
Here is where it gets a little more tricky. One input (I) word and one output (O) word are allocated for each group. Exactly what a group physically is depends on how you have configured your rack. (The rack is configured by dip switches on the backplane)

1 SLOT ADDRESSING:
If you are using 1 slot addressing, then one group = 1 slot. The advantage is it is easy to understand, with slot number corresponding to group number. The disadvantage is you waste the complimenatry I/O word in the IO image table - for every input card you place in the rack, you have an un-usable output word. If you put in output card in slot 0, then I:00 will always be empty in the IO image table.

2 SLOT ADDRESSING:
If you use 2 slot addressing, then physical slots 0 and 1 become group 0. Now you can put an input card in slot 0, and an output card in slot 1 (or vice versa-the PLC does not care) and each are I:00/0-I:00/17 and O:00/0-O:00/17 (octal). You must however pair an input card with an output card.

1/2 SLOT ADDRESSING:
If you use 1/2 slot addressing, then each module will occupy two groups. You use 1/2 slot addressing with 32 bit IO modules.

Rack:
8 contiguous groups in a chassis constitute a rack. Do not confuse chassis with rack. A 12 slot chassis contains two racks in slot addressing, rack 0 and rack 1, whild in 1/2 slot addressing it is 3 racks.

Well by now you are probably lost. Lets try this for an example.
We have an 8 slot chassis, alternatviely populated by 16 bit input and output cards, Input in slot 0, output in 1, input in 2, output in 3, etc.

If the chassis is configured for 1 slot addressing:
The 8 slot chassis comprises 1 rack.
These are the valid IO address:
I:00/0 - 17
O:01/0 -17
I:02/0 - 17
O:03/0 -17
I:04/0 - 17
O:05/0 -17
I:06/0 - 17
O:07/0 -17

If we had a 12 slot chassis, then we could continue on, but with a new logical rack:
I:10/0 - 17
O:11/0 -17
I:12/0 - 17
O:13/0 -17

Now with an 8 slot chassis configured for 2 slot addressing, the chassis is one logical rack and valid addresses are:
I:00/0 - 17
O:00/0 -17
I:01/0 - 17
O:01/0 -17
I:02/0 - 17
O:02/0 -17
I:03/0 - 17
O:03/0 -17

Notice that we are making more efficient use of the IO image table. However, we must pair an ouput card with an input card, no grouping of all inputs cards together. If we have a 12 or 16 slot chassis, the chassis still comprises one logical rack and we can continue with addressing -
I:04/0 - 17
O:04/0 -17
I:05/0 - 17
O:05/0 -17

OK, now lets consider the 1/2 slot addressing in an 8 slot chassis. Now the 8 slot chassis will be two logical racks - each slot occupies two groups. If we put a 32 point input card in slot 0 and a 16 input card in slot 1, then slot 0 comprises groups 0 and 1, and slot 1 comprises groups 2 and 3. Addressing is as follows:
I:00/0 - 17 <- 1st half of 32 point card.
I:01/0 - 17 <- 2nd half of 32 point card.
I:02/0 - 17 <- 16 point input card.
I:03/0 - 17 <- This I word will be used, but always empty.

Continuing with our 1/2 slot chassis, if slot 4 contains on output card, then it is in rack 2, group 0, so the addresses are
O:10/0-17.

If I have completely lost you now, then download this manual

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1785-um012_-en-p.pdf

and look at page 45-50. There are some helpful diagrams on pages 47-49.
 
Last edited:

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