Correct I/O Card installation in PLC-5 system

hkg

Member
Join Date
Jul 2006
Location
HKG
Posts
8
Hi all,

Current configuration of the PLC-5 chassis is as follows:

All dc DI cards are placed left-most position which are closest in the chassis to the PLC-5 processor. Then the dc DO cards. We didn't have any AI,AO cards at all, and there are some racks in the chassis which are blanked.

Now we need to expand our PLC system by additional dc DI/DO card, we need to just simple place those new cards into the blanked rack? Or we need to re-adjust the placement order in the chassis (such that all DI cards (current or new installed) placing the left-most position first)?

We found the placement order priority in the Allen-Bradley PLC-5 manual and they did mention we need to place all DI cards in the left-most position first.

Please help! Thank a lot!
 
That's a good question, hkg, and worth asking.

From your post above, I am not certain about the placement of I/O modules you describe.

Are the input cards next to one another, but grouped to the left side of the chassis ?

Example: I / I / I / I / O / O / O / O

If so, you have "one-slot" addressing and may place Input or Output cards anywhere you wish in the chassis.

Or are the input cards and output cards placed in alternating slots ?

Example: I / O / I / O / I / O / I / O /

If so, you have "two-slot" addressing and must continue to adhere to the Input / Output alternating sequence. You may leave gaps in the slots, but may only place an input module next to an output module.

You will be able to determine the exact addressing mode of your chassis by examining the DIP switches behind the CPU or network adapter in the leftmost slot.

There are other variations on the Remote I/O addressing scheme, including 1/2 slot addressing and Complementary I/O. Check the DIP switches to be certain how your system is set up.
 
Last edited:
Thanks for your information!

Yes, in our system, the input cards are next to one another, but grouped to the left side of the chassis ?

That's : I / I / I / I / O / O / O / O

And we are using 'two-slot' address as the DIP switches setting.

So if we need to add new dc I/O card, this is simply just add to the blanked rack?
 
Greetings hkg ...



somehow we’re not understanding each other ... first of all, if you ARE using “2-slot” addressing, then the module configuration that you’ve shown would NOT work ... please read what Ken said again ... if you’re still having problems, it would also be a good idea to tell us EXACTLY what type of modules you have installed in each of the slots in your chassis ... be sure to give catalog numbers (example: 1771-IAD, etc.) ...



secret handshake: some “digital” modules require different setups (example: 32-bit modules have different requirements from the more common 16-bit modules) ...



the picture below shows the best way to determine which addressing mode (2-slot, 1-slot, or half-slot) that your LOCAL CHASSIS is using ...



hkg.JPG





IMPORTANT: note that this method only works for determining the addressing mode of the LOCAL CHASSIS (the chassis that has the processor in it) and NOT for any other (remote) chassis that might be connected to your system ... if you are using a remote chassis, let us know and we’ll go further ...



I think that what you’re basically asking is this:



suppose that I still have empty slots available at the right-hand end of the chassis ... can I install a new digital module in one of those empty slots - or do I have to rearrange my existing modules so that ALL of the digital INPUT modules are grouped together - and ALL of the digital OUTPUT modules are grouped together? ...



if that is your question, then the answer is that (in MOST cases) you CAN go ahead and just put the new module into any of the empty slots ... specifically, it is not required that all digital INPUT modules be grouped together - and that all digital OUTPUT modules be grouped together ... in some cases, such “grouping” is recommended by the “book” - mainly to minimize the transfer of “signal noise” from one module to another ... but ... there are MANY cases out in the field where the different types of modules are “mixed together” without any problems at all ...

if the existing setup that you posted above is actually correct - and already working - then you probably will be able to insert the new module into any of the empty slots in the chassis ...
 
Last edited:
I believe the OP is referring to this page of the PLC 5 user manual:

plc5untitled.JPG

In that case, what Ron wrote below should apply.

Ron Beaufort said:
if that is your question, then the answer is that (in MOST cases) you CAN go ahead and just put the new module into any of the empty slots ... specifically, it is not required that all digital INPUT modules be grouped together - and that all digital OUTPUT modules be grouped together ... in some cases, such “grouping” is recommended by the “book” - mainly to minimize the transfer of “signal noise” from one module to another ... but ... there are MANY cases out in the field where the different types of modules are “mixed together” without any problems at all ...
 
Thanks for you guys' sincere assistance!

For the Input cards, they are all 32-points dc modules, and for the output cards, they are 16-points dc modules.

Moreover, those cards are inserted into the remote I/O chassis via the remote I/O adaptor. We understand that this might work by just simply insert those new cards into the empty slots but we did felt quite puzzle why the AB manual (as quoted from grs) gave such recommendation.

Indeed I have consulted the local AB office, but no one gave us a concrete answer (although they are our consultant during our system development).
 
there's still something fishy going on here ...

Greetings hkg ...



well, if YOU’RE ok - then WE’RE ok ... but something is still not making sense ... if I’m reading your posts correctly then your system can’t be working properly ...



That's : I / I / I / I / O / O / O / O

And we are using 'two-slot' address as the DIP switches setting.



this won’t work ... with “two-slot” addressing, your discrete input modules and your discrete output modules would need to be placed in “I/O groups” ... that’s Allen-Bradley talk for:



“IOIOIOIO” ... or



“OIOIOIOI” would also be ok ... but you don’t see that order used as often ...



and if you really wanted to get crazy with it, then



“IOOIIOOI” would also work too ... or (equally crazy) ...



“OIIOOIIO” would also work ... but ...



“IIIIOOOO” as you posted earlier - that’s just not going to work correctly with two-slot addressing ...



side trip for those who won’t sleep tonight wondering “what would happen?” ...
let’s confine this to 16-bit modules for now ...



suppose that we have two output modules INCORRECTLY located together in the same two-slot group ... if a (shared) output bit in the two-slot group has a “1” status, then BOTH output screws would be energized (example: giving O:002/4 a “1” status would turn on BOTH output screws assigned to bit number “4”) ...



suppose that we have two input modules INCORRECTLY located together in the same two-slot group ... if EITHER input screw in the two-slot group has an “ON” signal (current flow), then the (shared) input bit will have a “1” status ... specifically, the two input screws work in an “OR” configuration (example: connecting an “ON” signal to EITHER of the “bit 5” input screws, would result in a “1” status at I:001/5) ...



note to beginners: this is NOT the way to set up a system ... we’re just kicking ideas around here - wondering “what would happen?” ... you should NOT attempt this in a "real" system ...



come to think of it, I might not be able to sleep tonight now that I DO know what will happen ...




the “basic idea” key is that when using 16-bit modules with two-slot addressing, no PAIR of slots may have two input modules OR have TWO output modules ... as long as you don’t violate that basic rule, then things usually work ok ...

showing the modules with spaces between the groups might make it more clear ... note that the spaces below should NOT be empty slots ... I'm just trying to show the two-slot "groups" that we're talking about ... and the following examples are ALL using 16-slot modules ...

"IO IO IO IO" is ok for two-slot addressing ... (most commonly used)
"OI OI OI OI" is ok for two-slot addressing ... (rarely used)
"IO OI IO OI" is ok for two-slot addressing ... (weird)
"OI IO OI IO" is ok for two-slot addressing ... (weird)
"OI IO IO OI" is ok for two-slot addressing ... (sadistic) ...

but ...


"II II OO OO" (as you posted) is NOT ok for two-slot addressing ...

notice that many of these "ok" patterns clearly violate the commonly accepted "rule" that says: "two-slot addressing requires input, output, input, output, etc." ... this is one of the little (educational) tricks that I play on some of my more advanced students ... as soon as they see one of these "scattered" patterns, they naturally assume that the system can't be using the two-slot addressing mode ... wrong answer! ...


For the Input cards, they are all 32-points dc modules, and for the output cards, they are 16-points dc modules.


now we’ve come to 32-point input modules ... this is an even bigger “issue” than the order of the input modules and the output modules in the slots ...



here’s a handy little “cheat sheet” that pops up in RSLogix5 when you keep following the links from the “Help” button shown on the screen in my post #4 above ...



addressing_help.JPG




sorry hkg, according to this, “you-can’t-get-there-from-here” ... everything that I’m saying in this post keeps pointing to the fact that something is wrong with what you’re posting ... if your system IS indeed running, then we can’t argue with success ... but I’ll bet (significantly more than pocket change) that this chassis is NOT using the two-slot addressing mode the way that you think it is ... that might be something that you’ll want to look into when you get some spare time ...



if I had to guess, I’d say that your confusion MIGHT come from the following source ... I’ve actually run into this situation ONCE while helping to troubleshoot a new PLC-5 system being installed in the field ... (the REAL guru was away at the time - so I was trying to fill in ... I got lucky) ...



the next picture is cut from page E-4 in the PLC-5 Processor User’s Manual

DIPs_PLC.JPG


and the next picture is cut from page 2-11 in the 1771-ASB User’s Manual



DIPs_ASB.JPG


notice that even though we’re dealing with the VERY SAME I/O CHASSIS, we have to use a different pair of DIP switches to select the addressing mode - depending on whether we’re going to plug a PLC-5 processor into the chassis - or plug a 1771-ASB Remote I/O Adapter into the chassis ... this is what was confusing the engineers who were trying to set up the new system that I mentioned earlier ... they were installing an ASB adapter in a remote chassis, but they had failed to notice that they were taking the DIP switch settings from the PLC-5 processor manual that they had handy ... oops! ...



anyway ... I’m out of time for today ... I’m not sure whether I’ve helped answer the original question from hkg ... or even whether hkg still HAS a question at this point ... but maybe some of this will come in handy for someone in the future ...
 
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A mistake!

Hi Ron and other good guys!

Yes, Ron is right!

I have made a mistake just as what he highlighted!! I have mixed the chassis which PLC processor located and those for the Remote IO adaptor (1771-ASB).

The system that we are now running is using 1/2 slot addressing. Then everything's clear! Two identical chassis, if they are inserting with different AB cards, then the meaning of the SW would be different!

Sorry that I place a primary school problem into the forum!

I would like to take this oppotunity to give my sincere thanks to Ron, Ken and Grs for their helpful support!
 
Greetings hkg ...

Sorry that I place a primary school problem into the forum!

please don't apologize! ... actually these Allen-Bradley PLC-5 "addressing mode" issues aren't what most people would call a "primary school problem" ...

consider that the system can use two-slot, one-slot, or half-slot addressing modes ... consider that each chassis in the same system can be set up with a different addressing mode ... consider that the discrete modules may have 8-points, 16-points, or 32-points ... then consider that a different pair of chassis DIP switches must be used to select the addressing mode - depending on whether the chassis contains a PLC-5 processor - or if it contains a 1771-ASB Remote I/O Adapter ...

and we haven't even mentioned analog modules (and other specialty modules) which require Block Transfer operations ... and we haven't covered "complementary addressing" either ...

thanks for bringing the topic up for discussion ... and you're quite welcome ...
 

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