Putting PLC 5 into Program mode

Hello:
I have a primary and a backup PLC-5.
One way to turn the primary into the 2ndary is to turn the key switch.

Is there an alternative to put the primary processor into program mode in RS logix?
Ie. a bit you can toggle to put the processor in program mode?
Thanks in advance,
George

I'm confused, as long as the PLC Keyswitch is in REMOTE, you can switch the CPU between run/prog/test from within RSLogix. Either from the 'Status' toolbar, or from the Comms menu under Mode.

Yes you are correct, the problem I hear is this:
If you are in ONLINE with primary PLC (say station 26)in RS logix, you can put it in program mode.
But as soon as you do that, the Backup PLC (say station 27) becomes station 26, but the RS logix looks at the 26, and puts that in program mode as well. Now both plcs are in prog mode, and we just shut down the production line.
This was a problem I hear with the 6200 software, I am not brave enough to try this on the new software.
So this brings me back to the question of whether there is a way to put the primary plc into prog mode without this potential problem of putting both plc in prog mode.
thanks again.
George

Is this a hot backup over ControlNet? If so then you can switch using the interface in RSLogix. I can't remember how to get to it but I remember in the past forcing switchovers this way when I was testing a system. If this is a hot backup using the BEM modules then I don't know...

You are correct, we are using BEM modules for hot backups.

George:

Have you experienced the "double program mode", or is this just something that you've heard?

I've had some difficulty with doing somehthing similar to this, when I've accidently tried downloading a program (containing a bunch of changes) to the primary instead of the secondary PLC, and the switchover occurs during the download, confusing both the PLCs and RSLogix.

When dealing with BCM/BEM PLC's, I follow these rules:

1) Connect only through the DF1 port (or ethernet port, if available), not via Data Highway. This way I don't accidently get "bumped" off the PLC that I think I'm working on.

2) Only make changes to the secondary PLC. That way, if something goes wrong, the primary is still in control, with a good program.

One technique I've used to trigger a change-over is to write a negative value to an active timer (I usually have one timer as a "one-second pulse" that's running all the time.) Do that when online with the primary (violating rule #2), and it will fault, and the secondary will kick in.
Needless to say, this should be done on a timer which is not being synchronized by logic.

I've had some peculiar things happend with BCM/BEM module systems. I've made online changes to the primary plc, and when I went to make them to the secondary (with no switchover) THE CHANGES WERE ALREADY THERE! (This is the reason for rule #2).

Hello Allen:
I'm not 100% clear as to how you are using the timer technique.
Is it just a free running timer? and how are you giving it a negative value, is it the preset value you are making negative?
George

Devil is in the details.

Yes, the one I use is just a self-reseting timer (XIO T4:0.DN TON T4:0)

And Yes, I write to the Timer preset using RSLogix. This faults the PLC, but only the one that I was online with.

Powering down the primary PLC is NOT an option, BTW. I tried that once, and the secondary STAYED SECONDARY!!! The secondary PLC's BCM module never got a message from the primary saying that there was a problem, and so didn't take over.

I never liked those things. Not worth the effort, IMO.

I don't think RS logix allows you to put in negative numbers when you are under rung edit mode. I have a test station here and it simply won't accept them. I have version 5.50.

The trick is...

It won't just let you enter a negative preset in the TON block.

It will let you enter a negative value in the data table.

Can you spell BUG?
[flipv][fliph]U-N-I-N-T-E-N-D-E-D- -F-E-A-T-U-R-E.[/fliph][/flipv]

AH HA!
I see what you mean there,
Ok now if I the fault station 26 by putting -10 into a free running timer, the back up will take over, correct? but 'will' this create the problem where the back up station 27 becomes 26 and then it will put -10 into that as well, thus faulting both PLCs?
I guess the question is, if you are online with station 26 and you fault it, which PLC will the RS logix show?
I am assuming it will stay online with the faulted one, which will change its station number from 26 to 27?
Thanks,
George

Danger, Will Robinson.

No. You shouldn't get a double fault (at least I didn't used to). RSLogix will only write once to the PLC when you enter the number.

But RSLogix may act a little "weird", because RSLinx has it connected to the PLC at DH+ station #26, and that will suddenly be the secondary PLC. I wish I could be more specific about the "weird", but it was a few years ago that I did this, and it wasn't anything I could put my finger on, just a feeling that what I was looking at on the screen was not what was actually going on with the process.

Again, you're best bet is to go online via the DF1 port, not DH+, if at all possible.

---

This is about where I say that any tests you try, you try at your own risk. You are responsible for the consequences, not some semi-anonymous poster on an internet bulletin board.

I.E. Don't blame me if it doesn't work

Haha,
Thanks Allen, I like your cautious approach.
Anyhow, I will take the faulting method as the last resort. Just the thought of faulting the thing is uncomforting.
I heard there is a bit that you can set to put the processor in program mode. I will let you know what i find, thanks very much for your advance and time so far.
I'm starting to like this messaging board!! Good stuff.
George

Hi Allen,
One thing you have to look out for when faulting a processor by the
-ve value is that it doesn't send that value to the secondary plc.
meaning you've have to know the BCM BTW, BTR scheme well before taking that risk. Otherwise, both proc. will fault.

georgeofthejungle02 said:

One thing you have to look out for when faulting a processor by the [negati]ve value is that it doesn't send that value to the secondary plc.
meaning you've have to know the BCM BTW, BTR scheme well before taking that risk. Otherwise, both proc. will fault.

Click to expand...

I believe I said that, but not in so many words:

Allen Nelson said:

Needless to say, this should be done on a timer which is not being synchronized by logic.

Click to expand...

Perhaps the bits you are looking for are the S:1 bits, lower nibble.

If S:1/0 is set and all others reset, the PLC is in Remote Program
If S:1/1 and S:1/2 are set, and all others reset, the PLC is in Remote Run.

I've never tried actually writing to these bits (at least not intentionally), so I can't say for sure that they control the PLC (as opposed to reading the status of the PLC), but if you're game, you can try them.

Again, don't sue me if it doesn't work.