Remote I/o Not Controlling Outputs

from tomalbright:

And Ron, you were half right...

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well, OK, Tom ... the problem is that I still don’t see the “half” where I was “wrong” ...



for one (minor) thing, the manual that you linked is for the “Classic” PLC-5 processors ... but the PLC-5/11 is an “Enhanced” type ... so a better manual to use would be the User Manual for Enhanced and Ethernet PLC-5 Programmable Controllers ... but that still doesn’t change things ... even in the manual that you linked, on page 4-12 it says this:








and that rule (I’m quite sure) holds true even for the enhanced processors ... the way I see it, you’re trying to use “complementary” addressing for mholt’s system ... but the fact is that he only has TWO chassis - and one of those is the “processor resident local” chassis ... and you can’t set that one up as “complementary” ... and ... even if you COULD, that chassis is NOT going to be assigned as “Rack 03” ... and THAT presents an insurmountable problem - because any Remote I/O connected to a PLC-5/11 MUST be assigned as “Rack 03” ... and ... the only way to “complement” two I/O chassis is to give both of them the same “rack” address ... oops! ...



and so, we can’t get there from here ... specifically, the “local” chassis can NOT be “Rack 03” - but the “remote” chassis MUST be “Rack 03” ... this is one reason why the two chassis can NOT be set up for complementary addressing ...



I’m still not sure what you mean by the rest of your statements in Post #15 ... but I’m willing to bet a LOT more than pocket change that this suggestion isn’t going to work:

Try the outputs numbered by group address... Use beginning addresses I:030/00 for the first module, I:030/07 for the second, and O:031/00 for the third, etc.

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I’m convinced that won’t work ... first because mholt’s list only shows TWO modules in that remote chassis - not THREE as you seem to have in mind ... but more importantly, he’s already confirmed the actual addresses for those two modules with this statement in Post #14:

for clarification:

The addresses for the input card are I:030/0-17
The addresses for the output card are O:030/0-17

I was programming on it not to long ago and that is how they are addressed.

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which goes right along with what I forecasted back in Post #7:

the input module should have the following addresses:

I:030/0 through I:030/17 ...

the output module should have the following addresses:

O:030/0 through O:030/17 ...


note that this conflicts with what my colleague tomalbright posted - but I still think that I’m right ...

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now then ... I think that if we leave the “complementary” addressing behind - once and for all - then everything will start making a LOT more sense ... specifically, let’s just have the “local” chassis set up for “two-slot” addressing - with the eight existing 8-point modules tucked into the 8 chassis slots ... and then let’s also just have the “remote” chassis set up for “two-slot” addressing (for consistency) - with the two existing 16-point modules tucked into the first 2 chassis slots ... that should give us something like this:








note that setting up the “I/O Configuration” table is NOT necessary on a PLC-5 system ... but I just did it for “documentation” purposes - to help nail down the ideas involved here ...



anyway ... I’ve devoted as much time to this as I have available for right now ... if I’m “half” wrong, then so be it ... this won’t be the first time ... but ... actually I’m still convinced that I’m totally right ...



that being the case, I’d certainly appreciate it if you could show me where I’m making my mistake ... personally, I’m always ready to learn something new ... that’s what makes this job so much fun ...



party on ...

I'm looking at the PLC5 manual you linked to, however, let me clarify something... WHICH chassis is he having trouble with, the local or remote? I may be confused.

More than usual.

ETA: Yeah, complementary IO is old news here... It doesn't apply other than in theory discussion. So far, (as I am reading) the manual you linked to gives the same answer I did on 2 slot addressing. I've never encountered 1771 IO where this IO usage didn't apply.

tomalbright said:

Nope. Take a look in the "Classic 1785 PLC-5 Programmable Controllers Users Manual Page 4-13". That's the complementary addressing table for 2-slot addressing. Unless you are doing complementary addressing with a second chassis, you use up the module space for both "I" and "O" addresses in a module group. While the manual doesn't exactly explain the addressing, the chart shows that it is there and how it is used.

(There's a LOT of AB manuals on 1771 products... they really need to index them.)

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Sorry, Tom, but Ron's right....Take a look at 4-3. In 2-slot addressing, pairs of Input/Output modules use the same image. So, I:030/0 and O:030/0 are correct, not I:030/0 and O:031/0....that would be 1-slot addressing. I've only used two slot addressing one time where we had several racks with Input/Output module pairs. If you are using Analog and such, I would recommend going with 1-slot addressing instead. Much easier to keep track of.

robertmee said:

If you are using Analog and such, I would recommend going with 1-slot addressing instead. Much easier to keep track of.

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I will have to disagree here. See pic below, note 2 slot addressing for the local chassis. All analog, addressing makes for efficient use of the chassis. This is a working system.
If you look closely chassis 2 is 1/2 slot because it has some high density 32 point input modules.

robertmee, I WAS NOT confusing complimentary addressing, I used it as an example of how to use ALL the IO addresses. Let's leave that alone.

In 2 slot addressing, I am correct. 2 slot addressing uses two configurations - two 8 bit modules, (or two 16, one I, one O), correct? If you have, say, IIOO as the first 4 modules in a 2 slot addressed chassis, then the first two modules group address are always 0, and the second two are always 1. Thus, my 030 for the inputs, and 031 for the outputs is correct. If, though, you have 2 slot addressing, and use 16 bit modules, you can do as you indicate with addresses. In the original poster's config, he's indicated 8 bit, or 8 input modules.
Here's his IO:

PLC 5/11 PROCESSOR CHASSIS
SLOTS ARE LABELED A-H FROM LEFT TO RIGHT.

A) 1771-IB (12-24V) DC INPUT MODULE
B) 1771-IB (12-24V) DC INPUT MODULE
C) 1771-OB (12-24V) DC OUTPUT MODULE
D) 1771-OB (12-24V) DC OUTPUT MODULE
E) 1771-IA (120V) AC INPUT MODULE
F) 1771-IA (120V) AC INPUT MODULE
G) 1771-OA (120V) AC OUTPUT MODULE
H) 1771-OA (120V) AC OUTPUT MODULE

You can't address those OB modules as "0", but "1".

I'm not missing 24 years of PLC experience here... we ARE talking about 2 slot addressing, correct?

Mickey said:

I will have to disagree here. See pic below, note 2 slot addressing for the local chassis. All analog, addressing makes for efficient use of the chassis.

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I don't disagree that it can't be done. I just find it easier to keep track of using Rack/Group instead of Rack/Group/Slot in 1-slot vs 2-slot.

tomalbright said:

robertmee, I WAS NOT confusing complimentary addressing, I used it as an example of how to use ALL the IO addresses. Let's leave that alone.

In 2 slot addressing, I am correct. 2 slot addressing uses two configurations - two 8 bit modules, (or two 16, one I, one O), correct? If you have, say, IIOO as the first 4 modules in a 2 slot addressed chassis, then the first two modules group address are always 0, and the second two are always 1. Thus, my 030 for the inputs, and 031 for the outputs is correct. If, though, you have 2 slot addressing, and use 16 bit modules, you can do as you indicate with addresses. In the original poster's config, he's indicated 8 bit, or 8 input modules.
Here's his IO:

PLC 5/11 PROCESSOR CHASSIS
SLOTS ARE LABELED A-H FROM LEFT TO RIGHT.

A) 1771-IB (12-24V) DC INPUT MODULE
B) 1771-IB (12-24V) DC INPUT MODULE
C) 1771-OB (12-24V) DC OUTPUT MODULE
D) 1771-OB (12-24V) DC OUTPUT MODULE
E) 1771-IA (120V) AC INPUT MODULE
F) 1771-IA (120V) AC INPUT MODULE
G) 1771-OA (120V) AC OUTPUT MODULE
H) 1771-OA (120V) AC OUTPUT MODULE

You can't address those OB modules as "0", but "1".

I'm not missing 24 years of PLC experience here... we ARE talking about 2 slot addressing, correct?

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Yes, 2-slot addressing, but read the configuration again. We are discussing the remote rack (#3) which has two 16 bit modules. So, 030 would be correct for Input and Ouput, not 030 and 031.

Yes, that's true...

That one will work with 2 slot correctly.

robertmee, I got the email... I'll answer your question.

I think we got off on a tangent. For 8 bit, 2 slot addressing (which we didn't need in this topic, actually) I was right. In this topic, using 2 16 bit modules, Ron was right. If we were to discuss 2 slot addressing, 8 bit modules, I'm sure he would have agreed with me; it appears we went off on a wild ride here, partly due to me and doing some (too quick) reading of the OP. I had started my guestimating before the IO was listed, and carried on...

ETA: I've worked with this stuff for a while, and honestly the 1771 stuff, other than some PLC5's I use, is really old hat. That's all I used "way back", though! PLC3, PLC2, etc.

tomalbright said:

robertmee, I got the email... I'll answer your question.

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It took me a moment...I'm like, what e-mail? I remember now, I asked you an 'insiders' question months ago...I've heard of snail-mail, but geesh

Check your PMs.

Greetings to all ...



first from tomalbright:

Ron was right.

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thank you, Tom ... not that my ego was bruised - but I just couldn’t imagine where I had been making a mistake ... now going further ...

I think we got off on a tangent ... it appears we went off on a wild ride here, partly due to me and doing some (too quick) reading of the OP. I had started my guestimating before the IO was listed, and carried on ...

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I think that’s EXACTLY what happened ... the original post from mholt didn’t nail down whether he was using 8-point or 16-point modules ... so ... what you were posting didn’t NECESSARILY line up with the “remote chassis” problem that he was having trouble with ... and THAT’S what I was offering to discuss with you by phone in my PM “way back when” ...



anyway ... I’m OK if you’re OK ... let’s move on ...



for those who care, the analog modules used in a PLC-5 system have DIFFERENT rules ... we can dig into that for those who are interested - but here’s a “big picture” idea just for starters ...



the PLC-5 processor uses Block Transfer instructions to transfer information to and from the analog modules ... so ... the addresses of those modules don’t land on the input and output data files ... that means that the analog signals don’t have “I:” and “O:” type addresses ... so ... those modules don’t have to obey the same rules about using INPUTS and OUTPUTS in the same IO groups ... so as a specific example, it’s quite possible to have 2-slot addressing and have IIIIII (that’s six ANALOG input modules) all in a row ... you couldn’t do that with the digital/discrete modules - but it can be done with analogs ... that’s all I’m going to say about that subject for now - but we can dig deeper if anyone wants to ...



one more thing ... it is COMMON to think that using 16-point modules with 2-slot addressing requires that the modules ALTERNATE like this:

IOIOIOIO ... now suppose that Technician Ted is looking at a system and sees the following pattern: OIIOIOOI ... now it’s completely logical for Ted to think that 2-slot addressing is NOT being used here - because the modules don’t match up with the “alternating” pattern what he’s always seen before when using 2-slot addressing ...



but ... (and here’s the trick) we certainly COULD be using 2-slot addressing after all ...



the reason is that EACH GROUP (of two slots) can only have ONE 16-bit INput module - and ONE 16-bit OUTput module ... BUT ... there is NO RULE on how those modules must be arranged WITHIN each group ... to make this easier to see, I’ll put the same pattern in again - and this time I’ll separate the “groups” with dashes:



OI-IO-IO-OI ...



and so, we’ve obeyed the “one INput and one OUTput” rule for each group - and the system will work just fine ...



NOTE: remember that we were talking about 16-point modules in that discussion just above ... as tomalbright pointed out, the rules are different when you use 8-point modules ...



which brings us to the next topic ... I think I’ll start another post for this one ... but before we leave this one, here’s one more quote from tomalbright that I’d like to mention ...

I've worked with this stuff for a while, and honestly the 1771 stuff, other than some PLC5's I use, is really old hat.

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I just want to say, for the record, that the 1771 hardware - and PLC-5 systems - might be “old hat” - but there are still TONS of that stuff out there ... the hardware is still being made ... and it’s still being sold ... and it’s still being used ... and I’ll guarantee you that knowing the type of material that we’re covering here is CRITICAL to the maintenance technicians working in MOST plants that use Allen-Bradley systems ...



now most of you know how I make my living ... while I’m getting more and more requests for ControlLogix classes these days, at least 19 out of 20 of my customers are here for training on the good-old-rock-solid PLC-5 systems ...



and incidentally, the same two-slot, one-slot, half-slot addressing modes that we’ve been discussing for the PLC-5 can also come into play for the SLC-500 systems - when they use Remote I/O hardware ... and ... also for the ControlLogix when it’s connected to existing “legacy” hardware ...



now on to the next post ...

a little lesson from the PLC Boot Camp ...

here’s a handy trick that I always cover in every PLC-5 class ... each student has his own workstation station ... and yes, I know that I’m being politically incorrect by not saying “his or her” - but I’m old-fashioned enough (and just plain OLD enough) to get away with that sort of thing ... anyway ... in order to do the wiring exercises, each student needs to know what addressing mode he’s using on his particular station ... now we could pull the processor out - and check the DIP switches on the chassis backplane ... but that would require shutting down the system ... bosses don’t like that “shut down” stuff ... so, here’s a simple little trick ...



by going to the "Processor Status" file and clicking on the "Switches" tab, we can tell how the LOCAL chassis has been set up ...







now first things first ... this only tells how the PROCESSOR’S CHASSIS is set up ... specifically, any Remote I/O chassis in the system could be set up completely different ...



going further along that same line ... the following screen can be found under the RSLogix5 I/O Configuration feature ...








this one can get you in trouble ... the settings on this screen may be totally incorrect ... simple fact: this screen is all “documentation” and the processor does NOT “read” it - or “update” it ... the first screen that I showed above (from the Processor Status file) actually DOES get updated from the processor ... but this one from the I/O Configuration can be totally wrong ... blindly relying on this particular screen has caused a LOT of confusion for technicians in the past ...



anyway ... back to the first screen ... notice that if you click the “Help” button on that window, you can “drill down” through various links - and finally arrive at a handy little “cheat sheet” that can be helpful as a “getting started” point in understanding the two-slot, one-slot, and half-slot addressing modes ...



hint: when the chart says “I/O Pairs” it means that within a "group" (of two slots) you can have an INput type and an OUTput type - but not two of the same type ...

and now a bedtime story ...

while we’re on the subject, this was told to me as a true story ... I have no reason to doubt it ...



a rather large plant was involved in metal stamping ... hydraulic presses were pressing ... conveyor belts were conveying ... etc. ... etc. ... the boss was making money ... life was lovely ...



Bubba the operator would come in to work every day, and put his little jug of Gator Aid on top of one of the electrical cabinets ... whenever Bubba got thirsty, he would reach up and push the little spigot and get himself a drink ... this went on for many happy years ...



but ... the spigot leaked just a drop or two from time ...



Gator Aid is rich in electrolytes ... which means that it has a lot in common with saltwater ... and ... it corrodes the top of steel electrical cabinets ... and it also corrodes the connections on the back of a PLC-5 chassis ...



so ... the machines started acting up ... the technicians opened the cabinet to troubleshoot ... they found the sticky mess in the bottom and followed the trail up to Bubba’s jug of Gator Aid ... they also found that the chassis had been corroded ... luckily nothing had happened to the PLC modules, etc. ...



this looks like a job for Little Johnnie, the junior electrician ...

so Little Johnnie was told to go to the storeroom and draw out a spare chassis (luckily they had one on hand) ... then replace the chassis ... the “Top Gun” technicians would be back after lunch to fire the system up and test it out ...



see it coming? ...



Little Johnnie swapped out the chassis and put everything back together ... the Top Guns finally showed back up and flipped the disconnect to the ON position ...



the way the story was told to me (supposedly true) the machinery went nuts ... presses crashed ... robots crashed ... and so on ...



can you guess what step Little Johnnie had left undone? ...



yep ... he didn’t notice the DIP switches on the chassis backplane ... so in effect, the control wiring for the plant’s equipment had just been readdressed from SOME-slot mode to ANOTHER-slot mode ...



moral of the story ... yes, training is expensive - but ignorance is where the REAL money is ...

Thanks Ron... when I say "old hat", don't mean unused! I'm running into a lot more SLCs these days, and even Flexlogix stuff.

The IO stuff you listed is pretty neat, I didn't want to get into all that, but it's definitely true, and can be a show stopper for a beginner.