AB PLC-5 Remote I/O Data

Thanks in advance for any feedback!

I have two questions.

1) I am adding functionality to an AB PV1200 (DOS w/ function keys). I have a user manual and can accomplish what is required but I do not understand how the block transfer data relates to the discrete data table in the PV. The original set up uses 1.5 files or 3 bytes of BT data, which shows up as used in the discrete data table in the PV. How is the 3 bytes of discrete data being utilized in the BT? The block transfers are 16 bit(words), 32 per file being used at this time.

2) There is an 12 bit analog output card in a remote I/O rack being read from a PLC-5/40. The data from the analog card is being read by block transfer. But the I/O data table in RSLogix5 shows the addesses of the remote rack. I may be incorrect, but in SLC500 remote I/O from an adapter shows up as 32 words even if they are not used. Is this the same with PLC-5? If you addess a remote rack it shows up in the data table even if it is not used by discrete addessing?

Greetings aiki202 ...

I have a user manual and can accomplish what is required

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I certainly don’t want this to sound “snotty” - but if you can do what is required, what is your question? ... do you just want to KNOW what’s going on for your personal satisfaction? ... (not that there’s anything wrong with that) ... based on that assumption, I'll try to explain it ...

I do not understand how the block transfer data relates to the discrete data table in the PV.

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there’s more to it than this, but here’s a simple analogy that seems to help a lot of people ... consider the Block Transfer operation as a “mailman” who carries the mail between the processor and the other device (in your case, the PanelView) ... consider the DATA being transferred as the information (message/letter) INSIDE an envelope ... in order for the mailman to deliver the envelope, he needs an address - located on the OUTSIDE of the envelope ... the one and a half words (three bytes) that you’re asking about can be thought of as the ADDRESS on (not inside) the envelope ... a little bit deeper: the bit patterns encoded in those three bytes are necessary to control the Transfer of the Block of information ...

There is an 12 bit analog output card in a remote I/O rack being read from a PLC-5/40.

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normally we don’t “read from” an analog OUTPUT card ... normally we “write to” an analog OUTPUT card ... (yes, there ARE exceptions) ... are you sure that you’re looking at the problem from the correct point of view? ...

I may be incorrect, but in SLC500 remote I/O from an adapter shows up as 32 words even if they are not used.

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that is basically correct ... the 1747-SN module EXPANDS the SLC’s input data table by 32 words - and it EXPANDS the SLC’s output data table by 32 words ...



going deeper: the SCANNER module is the “thing” that causes the expansion of the input and output tables that I just mentioned ... you used the word “adapter” - and not “scanner” in your original question ... technically speaking, the “adapter” is the thing at the FAR end of the Remote I/O line - not at the processor’s end of the line ... the ADAPTER part does NOT “cause” the tables to expand ... so, when you said that the “I/O from an adapter shows up as 32 words even if they are not used” then you’re technically incorrect ... specifically, IF (big IF) the system is set up correctly, the SCANNER at the processor’s end of the line will expand the data tables (32 words of input AND 32 words of output) ... but ... the ADAPTER at the far end of the line will only use as much of the data table space as it requires to do its job ... the usage is usually measure in units of “racks” ... a “full rack” of 8 words of input AND 8 words of output ... or a “half rack” of 4 words of input AND 4 words of output ... or a “quarter rack” of 2 words of input AND 2 words of output ...

Is this the same with PLC-5?

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no ... there are some major differences between how the PLC-5 and the SLC platforms handle their remote I/O ... the PLC-5’s input and output data tables are usually “frozen” in size and normally cannot be expanded ... (example: a PLC-5/40 has more “room” in its input and output data tables than a PLC-5/20) ...

If you address a remote rack it shows up in the data table even if it is not used by discrete addressing?

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I’ve tried reading this several different ways - and I’m sorry but I don’t know what you’re asking here ... you might want to rephrase your question ...



hope this helps ...

Thanks for the feedback!

Personal satisfaction...Yes. If you do not totally understand the system in which you are working, you might as well pack up and go home.

My last question rephrased: The I/O data table in RSLogix5 shows 1 word (16 bits) of data for Rack 3, Module Group 4, Slot 1. This is the analog output card. The analog output card has four 12 bit channels that are populated from the BTW in the ladder logic. How does the single word in the I/O data table relate to the 4 words of data in the card? Additionally, I am assuming that the card uses only 12 of the 16 bits of each word?

Personal satisfaction...Yes. If you do not totally understand the system in which you are working, you might as well pack up and go home.

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excellent! ... that's pretty close to my sentiments - except for that "totally" part ... there are very few things that I'd say I "totally" understand ... still - that's a pretty good goal to shoot for ...

The I/O data table in RSLogix5 shows 1 word (16 bits) of data for Rack 3, Module Group 4, Slot 1 ... How does the single word in the I/O data table relate to the 4 words of data in the card?

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simplest explanation: it doesn’t ... just consider that part of your processor’s I/O data table to be “wasted space” ... basically just STAY AWAY from it ... in MOST (but not all applications) some of the bits within that word might be used by the module to control its Block Transfer operations - so do NOT try to make use of any of the bits in that area for anything else in your program ...

Additionally, I am assuming that the card uses only 12 of the 16 bits of each word?

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that would depend on the SPECIFIC catalog number - and series - and revision number of the module that you’re working with - and on how that module has been configured ... best plan of attack: get the manual for your module ... there’s usually a “spreadsheet” style chart in there somewhere that shows what all of the individual bits mean ...



sometimes some of those “extra” bits are used for polarity signals, error reporting, etc. ...