a chain message:)

hmm, i have been programming PLC for a year now but still having hard time using advance programming..
a very basic question i wud like to ask, what is the necessity of moving a bit, word or double word to another destination?

example: in MITSUBISHI PLC
--(m8000)-----[MOV K3 D99]

and

--(M71)------[BMOVP D100 D1100 K10]
--(M22)------[BMOVP D1100 D100 K10]
(this moves data back & forth)

the only reason one would do something like that is to make program perform.....something.

for example your first rung sets value of D99 register to three. this is done to fix value (something that will be there even after PLC is powered down, program is dowloaded to new plc, making it read only so that nobody can change it even by accident etc.). note that not all registers are retentive and just because some of them are, they may loose content in certain scenarios. initializing values is common practice specially when same value used in several places in program and to simplyfy adjustment (edit one instruction instead of several).

your second example doesn't show much. yes there are two rungs that copy data back and fourth but we need to see what is real intent. for example you have machine that does some job where you have several parameters used by main program (let's say parameters are stored in D100-D109 of your example). if they are set correctly everything is fine and machine can run. but what if you want to be able to change those parameters without stopping machine? what if you have to change all of them at once before they are used by program? the most convenient way is to make a copy of the parameters to some other area (like D1100-D1109 for example) and allow user to make changes (all while original set of parameters is still running). once the changes are completed and machine is ready to start new process (bit M22) we can dump those changes back to area that is used by program.

as said, this is just an example of one possible scenario. the other can be to make backup of current parameters (by triggering M71), and allow editing of run parameters on fly (if editing one at a time is allowed). in case you are not satisfied with the result, you can restore default settings by triggering M22.

tnx a lot panic mode of toronto, that was very very very helpful hmm, can i ask anothr question? one rung on the program reads something like this..

----(M0)---------[= C10 K0]

this is a comparative instruction, and i was told that this is for positioning of the servo motor..i have known C as counter (for MITSUBISHI), is there any possible instruction that the C in the example above stands for?

are you sure you didn't swap the instructions?
comparison should be on the left and coil on the right.

[= C10 K0] checks if the counter C10 is zero (counter cleared).

Get PLC Instruction Manual.

that M0 was actuali a contact not a coil (sori for the ilustration)..
you said t'was checking if counter C10 is zero..i was looking for the instruction coil of counter C10 but i couldn't find..is this posible?

oh, anyway i was going over the program.. ive seen this insruction..

M8002
---//-----------[MOV K10 C10] @ the start of the process a value of
10 is moved to the counter C10..

another rung reads this one..

M54
---//-----------[= C10 K1]---------(M204)
[= C10 K2]-------/
[= C10 K3]-------/


i beliv it could be posible without the counter coil C10..tnx panic mode of toronto

...@ the start of the process a value of 10 is moved to the counter C10.

Click to expand...

Erika,

I think this comment means that somewhere in the program, there is a Counter C10. It could be in a subroutine.

The only alternative would be to manually move values into a "fake" counter, but why would anyone do that? It is much easier to let the counter count events as they happen.

Anyway, keep searching for that counter, and good luck!

uh,sounds like it couldn't be posible without a counter coil C10..i haven't checked for the sub routines yet..
what do you mean with fake counter?

hmm, can i ask you a question Lancie1??are you fmiliar w/ OMRON PLC??
i am looking for status flags (i.e. M8000, M8002, etc. on Mitsubishi) on its manual but i couldn,t find any..maybe, you could helpit would be greatly appreciatedi need a status flag to signify everytime my PLC is on, even without any operation taking place..tnx

there are no subroutine in the program..

what do you mean with fake counter?

Click to expand...

It is possible to move values into a Counter memory location, thus simulating the actions of a counter, but not really ever using the Counter coil or box.

Yes, I am familiar with Omron. I have written programs for the Omron ZEN, a very low-end PLC.

Erika,

Some of the Japanese PLCs call status flags "internal relays". Search for "Special Internal Relays".

[EDIT]: Wait! Did you write the comment about the Counter C10? I first thought this was a comment written by the program author.

But now I think that you might have written it as your intrepretation of what the rung is doing. If so, it may be that C10 is not really a counter at all. In some Japanese PLCs (Koyo, Direct Logic) I have seen the "C" used to mean a collection of special memory locations referred to as Control Relays.

Control relays ("C" type locations) are discrete bits normally used to control the user program. The control relays do not represent a real world device, that is, they cannot be physically tied to switches, output coils, etc. They are internal to the CPU. Because of this, control relays can be programmed as discrete inputs or discrete outputs. These locations are used in programming the discrete memory locations (C) or the corresponding word location which contains 16 consecutive discrete locations.

Click to expand...

hmm, that was my comment (the italized blue words)..i was trying to give interpretation of what the rung may mean..

uh, i see..so, it could be possible that C10 does not stand for a counter, but rather a relay..hmm, i will investigate on this further, thank you very much for the replyit's very much appreciated..

hmm, regarding OMRON special auxiliary relays..i was searching thru manuals & web searches but i couldn't find any for omron..il try to read on..but if you could give some examples of its special relay, i would greatly appreciate it..

thanks a lot Lancie1..

Is your PLC an Omron, or a Mitsubishi?

anyway, im just confused with the C10..i was told that C10 was used in positioning of the servo motor..(there are 4 positions in the program, just posted one)

if C10 is a relay, can it possible hold a value?..sori for being naive