Reseting All Instructions to Default

[SirCharles1]

Good day all. May your holidays be merry. When programming using RSLogix (the software used to program Allen Bradley PLC's), how can I have it so that when the processor is reset (turned off and then back on) the program with it's various instructions always goes back to default status. (Does it involve using the "status" bits?)

Thank you anybody and everybody.

 

[James Mcquade]

SirCharles1,

it all depends on how the program was written and what the intent was. by that i mean you simply can't reset code back to its initial state without knowing the machine.

i know of a machine that had its program set to initial conditions by the OEM and they had a power failure. when the power was restored, the machine tore itself apart trying to reset to home. $250k in damage.

Now to your question.

allen bradley plc's typically have a first scan bit that is set when the power is turned on or you go from program to run mode.
this is how i reset most of my code. Note i said most.
i reset rto timers,counters, latched bits, control words, and so on. CAUTION, you must know the machine, its operation, sequence, homing logic - everything.

I am stressing this because of experience and not wanting you to get someone injured. not trying to slam you in any way, just wanting you to be careful.

regards,
james

 

[SirCharles1]

Thank you very much

Yes. I understand your concern with regards to safety and/or the damaging of equipment. Is this bit and output energize?

Thanks again James.

 

[Mickey]

I have seen programs that have a subroutine that runs once at start-up to set all to a
"default" condition. ( timer presets, counters presets, outputs, data register values etc.)

 

[Brian123]

Yes. I understand your concern with regards to safety and/or the damaging of equipment. Is this bit and output energize?

Thanks again James.

If I'm reading between the lines correctly, I think you are misunderstanding what the PLC is providing you. There is no factory status bit that you can turn on to reset all the program instructions back to a proper state. (Of course, instructions that are non-retentive will return to a default state on a power-outage, but I'm guessing you aren't asking about those.)

What the PLC provides you with is a first-scan bit that you can use in an XIC instruction. This bit is only active for the first scan after power-up. You can construct a rung with this first-scan XIC instruction that will do anything you deem appropriate. This can include resetting retentive timers and/or counters, MOVing presets into various registers, even calling special subroutines as Mickey mentioned.

Bottom line is that there is no magical bit from the factory that you can OTE and have the program return to a known state. You get a bit that you can XIC and you need to do the heavy lifting yourself.

Brian

 

[SirCharles1]

Thank you Brian. I believe I understand. You read between the lines quite well.

 

[jdbrandt]

Bottom line is that there is no magical bit from the factory that you can OTE and have the program return to a known state. You get a bit that you can XIC and you need to do the heavy lifting yourself.

Brian

The key in Brian's response is the word "you".
"You" are the programmer, and as the programmer, "you" need to consider all states of operation...initialization being one of the states.

This question appears to be of the "initialization" type... The 'factory' cannot possibly know how you will be using (or, in rare cases, mis-using) the instructions they provide you, any more than a tool maker can anticipate how much clearance you have near a bolt or screw, when making a wrench or screwdriver.