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Old August 26th, 2009, 06:11 AM   #1
Lakee911
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PLC 5: Using O:000 and I:000 at the same time?

I have a program in RSLogix5 (PLC5) and when I click on the usage for I and O data files, I am using some of the same addresses for both inputs and outputs. How is this possible?

Please see the attached screen shot.

My understanding is that these should be indexed to the slot in the rack. I would expect to see, for example, I:000 in use and O:001 in use w/o duplicating addresses.

What's up?

Thanks.
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File Type: jpg io.jpg (59.5 KB, 265 views)
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Old August 26th, 2009, 06:28 AM   #2
Paully's5.0
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Do you have RIO on the system? If so that is how.
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Old August 26th, 2009, 06:43 AM   #3
Lakee911
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I don't think that I have any RIO ... but please explain how that would cause it.

Thanks,
Jason
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Old August 26th, 2009, 06:49 AM   #4
rdrast
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The rack is set up for "two slot" addressing.

In that case, each slot group has one input and one output range.

Example: Single slot addressing, 16 slot rack -
The rack is divided into two 'logical' racks, and each slot in each logical rack can have either an input or output module in any order.

Ttwo slot, 16 slot rack:
There is one logical rack, and 8 'Groups', each group has one possible input module, and one possible output module, but you cannot have two inputs or two outputs next to each other.
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Last edited by rdrast; August 26th, 2009 at 06:54 AM.
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Old August 26th, 2009, 06:50 AM   #5
iggy
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I believe you can set up the racks for 2 slot addressing (which you have shown) or single slot addressing.
2 slot addressing o:0 I:0 o:1 I:1 etc
1 slot addressing o:o I:1 I:2 o:3 etc
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Old August 26th, 2009, 06:54 AM   #6
Lakee911
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Come to think of it, I think they might be arranged input, output, input, output. Someone will be sending me a photograph of the PLC today to confirm.

Thanks
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Old August 26th, 2009, 08:19 AM   #7
daba
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Quote:
Originally Posted by rdrast View Post
The rack is set up for "two slot" addressing.
That is not necessarily the case.

It is possible that the rack is set-up for 1-slot addressing, and the I/O cards in question could be high-density 32-bit cards. In this situation the cards have to be alternated I.O.I.O etc., but each card "thinks" it is in two slots, so that the 32-bit image can be mapped to the I/O image tables.

The only way to be sure is to look at the switches in the rack behind the processor.

Last edited by daba; August 26th, 2009 at 08:27 AM. Reason: addendum
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Old August 26th, 2009, 09:05 AM   #8
TConnolly
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Quote:
Originally Posted by daba View Post
That is not necessarily the case.

It is possible that the rack is set-up for 1-slot addressing, and the I/O cards in question could be high-density 32-bit cards. In this situation the cards have to be alternated I.O.I.O etc., but each card "thinks" it is in two slots, so that the 32-bit image can be mapped to the I/O image tables.

The only way to be sure is to look at the switches in the rack behind the processor.
That is not quite right either. High density modules require the use of 1/2 slot addressing.


To the OP:
Quote:
My understanding is that these should be indexed to the slot in the rack.
In the PLC/5 you must be very careful in differentiating between Chassis/Slot (the physical mounting hardware of an IO module) and Rack/Group, which is the logical address of the IO module. I:000 refers to Rack 0, group 0, which may not necessarily be the first physical slot in a chassis.




See this post for detailed information on PLC/5 addressing - it also links the PLC/5 addressing manual.
http://www.plctalk.net/qanda/showpos...47&postcount=3

Other threads answering your question:
http://www.plctalk.net/qanda/showthread.php?t=21174

http://www.plctalk.net/qanda/showthr...31&postcount=1



Also, Unlike the SLCc500 which allocates IO image table words based on which card is actually in a system, a PLC/5 allocates one input and one output word for each group, even for empty slots and non-existent chassis - so the original programmer could use those mnemory addresses (or as our distinguished colleague Ron calls them, bit boxes) for anything he want to - although I wouldn't recommend it because IMO it causes confusion, you should still be aware that it could be done.


It may or may not be helpful to double click IO configuration in the project tree in RSLogix5. In RSLogix5 this is optional and is for information only, it doesn't affect actual operation of the system, so you are relying on whether the original programmer configured it or not. If it was configured it might help. The default is 1-slot addressing, so it if says 1-slot that may or may not be correct for what the actual system is. If however it says 2-slot or 1/2 slot (unlikely) then it was probably configured - the only way to know for sure is however is to check the dip switches on the chassis.
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Last edited by TConnolly; August 26th, 2009 at 09:33 AM.
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Old August 26th, 2009, 11:44 AM   #9
daba
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Quote:
Originally Posted by Alaric View Post
That is not quite right either. High density modules require the use of 1/2 slot addressing.
I beg to differ Alaric, 1-slot addressing is very common for 32-bit modules, I have seen it done loads of times.

What happens is that the module responds to both odd and even addresses, just as if the least significant bit of its slot address were masked off, meaning that the module will automatically "ghost" itself into the adjacent slot.

A 32-bit input module in slot 0 will therefore send its lowest 16-bits of data when slot 0 is addressed by the processor, and send its highest 16-bits of data, when slot 1 is addressed.

Since you must put an output (or no) card in the next slot, the output card will receive the outputs for slot 0 into its lowest 16-bits, and the outputs fro slot 1 into its highest 16-bits.
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Old August 26th, 2009, 03:24 PM   #10
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This is why I stressed that one has to be careful with Chassis -vs- Rack and Slot -vs- Group terminology when talking about PLC/5 IO addresses.

Quote:
A 32-bit input module in slot 0 will therefore send its lowest 16-bits of data when slot 0 is addressed by the processor, and send its highest 16-bits of data, when slot 1 is addressed.
The processor does not address slots. It addresses groups. In I:000 the first two digits, 00, refer to the logical rack and the last 0 refers to the logical group address in the rack. None of those numbers necessarily refers to a physical slot. So a 32 bit card in slot 0 uses the logical address group 0 and group 1 whether or not one slot or 1/2 slot address is being used and it is addressed I:000/0 through I:000/17 and I:001/0 through I:001/17 octal. If one alternates input/output card then one can conserve the IO image table, at which time you double the addressing size - ie, if alternating high density modules then double 1/2 slot addressing to one slot, if using 16 bit cards and alternating, double one slot addressing to two slot addressing.

If we keep that straight then we can understand what each is meaning instead of beating each other over the head trying to say the same thing.
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Old August 26th, 2009, 03:48 PM   #11
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Alaric,
You stated categorically "High density modules require the use of 1/2 slot addressing."

Then came back with "So a 32 bit card in slot 0 uses the logical address group 0 and group 1 whether or not one slot or 1/2 slot address is being used"

Who's beating who over the head ?
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Old August 26th, 2009, 05:25 PM   #12
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the plc might have complementary racks.
one rack will be inputs and the other will be outputs.

Aleric is also correct. unlike the slc 500 family, the plc5 will allow you to program unused outputs as internal memory bits.

regards,
james
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Old August 26th, 2009, 06:35 PM   #13
daba
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Quote:
Originally Posted by James Mcquade View Post
the plc might have complementary racks.
one rack will be inputs and the other will be outputs.
That is a misleading statement - "one rack will be inputs and the other will be outputs.".

You can mix I and O in each rack, so long as you complement them, i.e. where you have I at one address in one chassis, you must place an O in the other, or vice-versa, or leave one of the slots empty.

Complementing I/O to another rack is a similar technique to complementing I/O within a single rack when using 2-slot addressing (where 2 physical slots have the same Group address). This will only work for uni-directional I/O modules (eg. Digital In or Out). Higher level modules )eg. Analog In or Out), require both the I and O images at that address to control the Block Transfer mechanism for the Bi-Directional data transfers.

Complementing the I/O, whether this is done within the chassis using 2-slot addressing with 16-bit modules, or 1-slot addressing with 32-bit modules, or between chassis, will maximise the I/O capability of the processor, which has fixed size I/O image tables, depending on the model. There is a 16-bit word in each table for each R/G/S (Rack/Group/Slot) that the PLC5 variant can handle. Obviously without this "complementary" nature, 50% of each table would be unusable, halving the I/O capability of the processor.

Complementary chassis I/O is unlikely. In 22 years of working on AB systems, I have never come across an installation that used it. I'm not saying no-one uses it, it can get you out of a hole if you run out of rack addresses and can save you having to swap out the PLC5 to a model with larger I/O capability.

Back to the OP. Yes you can have inputs and outputs at the same logical address. The physical location of those I/O modules is most likely to be in the same module group in one rack, and could be 16-bit or 32-bit modules, depends on the addressing method configured. Less likely the I and O are in different racks, using complementary chassis.

As has been said before, a "must-have" is the rack dip-switch settings to determine the addressing mode.
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Old August 26th, 2009, 07:17 PM   #14
TConnolly
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Quote:
Originally Posted by daba View Post
Alaric,
You stated categorically "High density modules require the use of 1/2 slot addressing."

Then came back with "So a 32 bit card in slot 0 uses the logical address group 0 and group 1 whether or not one slot or 1/2 slot address is being used"

Who's beating who over the head ?
And you kept using "slot" when you should have been talking about "groups" I can certainly see someone who is new to PLC/5 addressing getting confused by a statement like "each card "thinks" it is in two slots" into thinking that two slot addressing is whats being talked about, especially since that how you would do complimentary input/output groups with 16 bit cards. The card doesn't think its in two slots, in fact it doesn't have a clue how the chassis is configured or even where it is in the chassis for that matter, all it does is report two groups of data.

What I am emphasizing is that a high density module requires two groups. One half of the IO on a HD card is portioned to one group and the other half is to the next group. You cannot assign an HD module any other way. If you arrange the modules in input/output complements then you can double your addressing scheme. But that does not change the fact that you must still use two groups to address the module.

One easy way to think about it is that HD cards need 1/2 slot addressing and regular cards need 1 slot addressing, and that you can double that if you alternate input/output cards for complimentary addressing, ie 1/2 doubles to 1 and 1 doubles to 2. I think its all covered pretty well in the other threads I linked, and those threads all have links to even older threads on the topic.

Apparently we can argue semantics all day long even though ultimately we are saying the same thing. IMO, this bit of tit for tat miscommunication reinforces the confusion that can be caused by referring to an IO address as a slot in the PLC/5.

Ultimately what we are about here is helping the OP understand how the PLC/5 addresses, and if we are to do that then we need to use the right terms.

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Old August 31st, 2009, 08:15 AM   #15
Lakee911
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I received a photo of the rack and by comparing the height of the rack to the width, I have determined that it's a 16-slot chassis. Most likely it is the 1771-A4B.

It is populated as follows:
  • Power Supply
  • Processor 5/15
  • 000: AC INPUT 120V -- Red Label
  • 001: AC OUTPUT 12 TO 120V -- Orange Label
  • 002: AC INPUT 120V -- Red Label
  • 003: AC OUTPUT 12 TO 120V -- Orange Label
  • 004: AC INPUT 120V -- Red Label
  • 005: POWER CONTACT OUTPUT -- Orange Label
  • 006: AC INPUT 120V -- Red Label
  • 007: POWER CONTACT OUTPUT -- Orange Label
  • 010: AC INPUT 120V -- Red Label
  • 011: DC OUTPUT 10 TO 50V -- Green Label
  • 012: ANALOG IN (12 BIT) -- Pink Label
  • 013: DC OUTPUT 12-24V -- Green Label
  • 014: ANALOG OUT -- Yellow Label
  • Empty
  • 015: POWER CONTACT OUTPUT -- Orange Label
  • 016: POWER CONTACT OUTPUT -- Orange Label
I think my numbering is correct.

According to the program, I have usage within the following registers:
  • O:000
  • O:001
  • O:002
  • O:003
  • O:004
  • O:005
  • O:007
  • I:001
  • I:002
  • I:003
  • I:004
So, which card goes to which register?

What registers are used for the analog input and outputs?
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