Toggle Bits

logix designer 5000 v21 to 32
trying to toggle input on bit will not turn on and the date table will not receive a 1.
This CLX PLCv21 is in rack with 1756 IB16, 1756 OB16, 1755 IB32, 1756 ENBT/A
training cabinet but no real input wired or outputs to the cards so is this why I can't get my toggling to work?
2.
But there is a PV 1000 also in these cabinet could this be use instead of real field device connected.
Trying to follow a class but not matching when I look at rack.
any help thanks.

Mad Max

Is it a physical input? As in, an input on the IB16? Those cannot be toggled programmatically, only forced.

Mad_ MAX said:

logix designer 5000 v21 to 32
trying to toggle input on bit will not turn on and the date table will not receive a 1.
This CLX PLCv21 is in rack with 1756 IB16, 1756 OB16, 1755 IB32, 1756 ENBT/A
training cabinet but no real input wired or outputs to the cards so is this why I can't get my toggling to work?
2.
But there is a PV 1000 also in these cabinet could this be use instead of real field device connected.
Trying to follow a class but not matching when I look at rack.
any help thanks.

Mad Max

Click to expand...

Hi, good morning! What I've always done is map my hard wired I/O to a DINT, such as DIGITAL_INPUTS and DIGITAL_OUTPUTS. So say you had a rung that needed an input from the card (hard wired) then map that in a separate routine to DIGITAL_INPUTS.0 for instance. Put that bit in the logic and you ought to be able to toggle that one. Hope this helps.

Hey Max,

Since this is a training station with nothing wired to it, open the module configuration for your input modules and select Inhibit. This will prevent the module from updating with new input data and will allow you to toggle any of the inputs without resorting to forcing.

Just for clarification, you are toggling the bit and it really is changing. But it is changing back so fast that you can't see it happening.

When you open the module configuration screen look at the field that says RPI. And let's assume it says 20ms. That means that every 20ms the module is sending data to the controller. So, you toggle the bit from 0 to 1 and it really does take it. But then within 20ms the module has sent the controller a 0 and overwritten your 1. If you can repeatedly toggle faster than that RPI rate, then it will work. But that obviously isn't realistic.

If you change the RPI to 750ms (the maximum allowed) and then toggle, you will probably be able to see your bit toggle on and then go back off again.

Inhibiting will prevent the module from updating so you can toggle any of the bits at that point. You only want to inhibit the input modules.

OG

EDIT: The PV wouldn't be writing to an input tag, so it is not likely that it is affecting your input. However, it would certainly affect other tags. If the PV were writing 100 to a setpoint tag and you were online in Logix 5000 trying to change it to 150, the PV would overwrite your change with the 100.

When you use the programming software to "toggle" a bit, it will certainly, and without doubt, do just that !!

BUT, if that bit is written to from another source then that will put it back again ....

You have to understand that the bit you have toggled in nearly all cases is written to by (a) something else in your code, or (b) data from input modules.

In either case, what you have already programmed or configured is driving the bit to the state it is programmed or designed to be, so a "toggle" from the programming software will appear to be useless. But the toggle from the software works, but 99.9999% of the time you will not see it, and 99.9% of the time it will not have any effect, it just depends on when you toggled it.

Try toggling the bit in program mode ....

If it is an internal bit, it will be observable to work 100%

If it is a bit coming from an input module, you almost certainly won't see it work. Disable the input module it is in, and you WILL see it work.

It is all about understanding about where the data comes from, how it is updated, and when it is updated.

Actually if you disable the scan in the IO tree Properties you can turn the inputs on and off.


Sorry what daba said ^^^

JaxGTO said:

Actually if you disable the scan in the IO tree Properties you can turn the inputs on and off.


Sorry what daba said ^^^

Click to expand...

Yes, my post tried to encompass all bits, internal and physical inputs