Problem to understand mitsubishi PLC logic

[parky]

Had a look at the program & there are a number of rungs where the logic does not make sense.
on rung 98 (And m33 or m33 an33) etc. this looks like someone who's lost the plot & been putting in ladder to try & solve a problem M17 can never energise?
if you look to energise m1 you need m33 m33 m17 = m1 however you need m33 not m33 to = m17
There are also many errors there is code after the end instruction + errors.

 

[Topcat]

Wow,I write robot software and this program has some issues .As was mentioned by "parky" A lot of the "M" registers are dead ends and disable half the rungs.Might be easier to start from scratch...
Here is an interesting rung ; What do you think , I dont know , does M204 ever get set ?? I would have to try it..

 

[parky]

Have you tried to verify the program, it has errors in it, if you change it you probably could not download it again without going into stl & removing the code after the end instruction.
This is almost some of the worst code I have seen, not quite though.

 

[mraj2001]

Problem in PLC program

Also in mitsubishi compare instructions use three bits i.e. m500 m501 m502 for < = > if the cmp instruction is programmed like: CMP D1 D2 M500 then bits 500 to 502 could be on dependant on the data in D1 D2, there are other instructions that use bits that may not be cross referenced in the program or they could be indirectly addressed i.e. m500Z will refer to the offset of the index register Z if Z = 2 then M500Z would refer to M502 if Z was 500 M0Z would point to M500.

I look in the manual that M496 to M511 are latched bits (battery backed).
In my case PLC was powered OFF for more than one month. How to set again latched bits if previous state is lost.

 

[Topcat]

mraj , the state of the bits you mention are set by the program code.The difference between say M100 and M500 is that M500 is remembered after the power is removed , M100 is not .If the PLC , or battery was not too old it could still retain the state after a month.This program contains a lot of bad code and mistakes , not a program I would try and learn on.I would spend more time on examples in the manual and or another better written program , to figure out how the code works.

 

[mraj2001]

Problem in Mitsubishi PLC

I believe the question is more simplistic than than the answers. Aj are you saying that the NO and NC contacts have no written labels so you cant identify what the contact does ? Thus making the determination that the statement is true or false very difficult.
Also in the Melsac language "X" equals an actual input to the PLC and "Y" equals an actual output."M" of the M100 you speak of is am internal register that is used to carry a true or false answer to be used elseware in the progam.
I could be wrong just a different take on the question...

Can you explain me how to correct wrong program code for latched bits.

 

[mraj2001]

mraj , the state of the bits you mention are set by the program code.The difference between say M100 and M500 is that M500 is remembered after the power is removed , M100 is not .If the PLC , or battery was not too old it could still retain the state after a month.This program contains a lot of bad code and mistakes , not a program I would try and learn on.I would spend more time on examples in the manual and or another better written program , to figure out how the code works.

Can you explain me please how to correct wrong code in the program for latched bits.

 

[Lancie1]

What do you think , I dont know , does M204 ever get set ??

Yes, I think M204 will get Set. But the rung appears to "do nothing", accomplishing the same thing as reading the Input for "X020 Trolly Up Photocell". It is either ON, or it is OFF. Adding extra Sets and Resets is NOT going to change that fact.

If X020 is ON, then DO THIS,
If X020 is OFF, then DO THAT.

No latches should be needed.

 

[TurpoUrpo]

No, there is that auto/man switch. it in fact seems to look if its switched from man to auto or vice versa and trolly is in some position, or m200 gets positive edge. Cant say much as dont know what that machine really does.

Bad programming none the less. Some programs from one juice/dairy package companys machinces come to my mind.

 

[Topcat]

Lanci what you say is true the line is of no use. My question comes from X003. When you have X003 and then ,on the rising pulse of X003 , then the rest of the line. Since the rising pulse of X003 only lasts for one cycle , do you have X003 on at the time of the rising pulse, to set M204.. ??? Kind of the chicken and the egg thing...I would not write this line ever but it caught my attention as an interesting thought. MrAJ software is not functional and we dont know if it ever worked..

 

[Topcat]

these are commands I am not familiar with , can any one help me with them..

SFTL m541 m501 k24 k24

My guess is that 24 bits of m501 are moved into 24 bits of M541

SFTLP M92 M501 K24 K1

?????????? why the "P" on the end ? In the line there is an "AND" M8012 clock pulse

Also in older software is M4000 a legal register?

 

[geniusintraining]

This is for the FX but it coveres GX developer

http://www.meau.com/Files/JY992D88101-D.PDF

Starting on chapter 2 are some of the common instructions

 

[Topcat]

Thanks Genius I dont use those commands, but I should have known what they were , senility setting in I guess.

 

[mraj2001]

Thanks to all helped me to understand the PLC program.
Tips I get from you all and manual downloaded from mrplc.com helped me to solve the problem.
I edited the program by making SET/RST logic for memory bits to run the output and now program is working well.


My best regards to the members of plc.net
geniusintraining
Parky
Viks
Sergei Troizky
Topcat
Panic mode

 

[helloankur]

do you know how to use instruction Drol and Dmov for shift register.