Trying to download program from Mitsubishi A172SHCPUN fails

[parky]

After being in this industry for over 40 years I think ther general consensus is that upload is from PLC to PC & download is from PC to PLC as it is the PC that is the master. i.e. you are the controlling factor.
Which ever way you call it, it is impossible to transfer an empty i.e. no project from the Pc as it will not have any idea what PLC it is or it will not have been compiled, only if you have a project that has the right PLC selected & a compiled program will it allow PC to PLC. When you manage to get your copy of the program ensure that the data tables have been copied while the machine is not operating i.e. in a state ready to start, this way any data held in registers will be what you expect when machine is ready to start.
One thing to be aware of is that it is possible that the program was written in GXIEC developer, this was the early version of GXWorks I do not have a copy now but as it used FBD language the code will come back not what you expected, in most cases it will work ok but I have had instances where it will not translate into ladder, GXIEC to get the re-constructed graphical representation requires the symbolic code to also be written to the PLC, this is rarely done as it takes up memory & very often there is not enough.
altghough not having GXIEC I cannot confirm if the A17xx motion PLC is in the list as it is rather old so it is probably unlikely supported in GXIEC just like GXWorks.

 

[lbcobra]

Hi,


I tried to "Read from PLC" to the PC using an Unset project without any luck. It allowed me to choose the PLC type/CPU. Having been in the embedded engineering world for 40+ year I assumed that the PLC was similar to a micro controller where the code could be downloaded and diss-assembeled. I guess our two worlds are somewhat different.


Thanks for giving it a shot.


len

 

[parky]

The code downloaded to the PLC is not actually compiled as such, when you create the logic ladder contacts they are just hex values for example LD X0.0 (Load X0.0) A X0.1 (AND X0.1) OUT M0 is just a bunch of hex codes. for example LD X0.0 might be HF723 (not The actual hex as I do not know what they are) but it probably F7 means load & 23 means X0.0. The PLC has a mini interpreter that scans through these hex values to determine the operation. so when you upload back to PC it is the hex codes, the IDE then interprets them back into ladder.
The later GXWorks is a bit different, as you can use what they call local labels i.e. variables that have no physical address the "compiler" allocates them at compile time in reality it does not compile them just allocates these local variables to the address map in the higher portion of the address space that is reserved. Did it give you the same error i.e. plc parameters memory settings different or something else ?.

 

[lbcobra]

In this world I feel like a fish out of water. Is there a de-compiler as such?


Does the device data option download the program area, or "scratch pad" memory. When I grab the data memory I can see a SW version that matches what is on the machine. I'm not sure if that grabbed the program or not.



Are these PLC's documented in detail anywhere so as they can be understood more clearly? We have a number of machines around the shop that use different makes of PLC's.Mechanically the machines are serviceable. It's where it comes to the controllers that things get dicey.


I truly appreciate your advice.


len

 

[lbcobra]

Sorry, just to clarify... When I say "download" I meant move data from the PLC to the PC.

 

[parky]

In most circumstances the comments (documentation) is only stored on the disk not in the PLC, however, on Mitsubishi from GXIEC to the latest GXWorks3 there is a way to download what they call the symbolic code, this is effectively the structure plus symbols & comments, however, depending on the memory left after the program has been downloaded there may not be enough room for the symbolic code, most engineers would not bother anyway for a number of reasons.
I.e. do not want any others to look or understand it (but as it comes back in ladder format it can be understood), not enough memory, just don't bother as it takes time & finally, often if they did download the symbolic file forget to update it when modifications are made so in general the copy on the PC needs to be maintained.
There is no real compiler as such (on many PLC's) as I stated, the code is just a bunch of hex values, the PLC has an interpreter that runs & takes the hex codes & processes them just like un-compiled basic does or used to. The IDE (pc application does the same thing it takes the hex codes & displays the ladder or statement list so it is more understandable.
The device data is two areas i.e. PLC Parameters this is where certain parameters can be set like I/O installed, how much memory is allocated for temps, File memory (extra retentive data) what areas are retentive , if a also timing, interupts & many others.
attached are two pictures one shows ladder without comments or symbols i.e. what will be in the plc as it is unlikely that the symbols file has been downloaded also at ther bottom is the statement list just effectively a display of the interpreted hex values much like assembler language of the ladder above the other is how documentation is displayed if you have a copy of the original file.
Assuming the symbolic was not downloaded then the only way of getting the documentation is approach the original programmer & hope they will give you a copy with the comments.

 

[parky]

Here is the later IDE using FBD & ladder far better for commenting & if you are used to logic symbols probably makes sense.

 

[lbcobra]

Thank you for giving it a try. I got another issue taken care of and the machine back online. For now I'm going to have to pass up on getting a backup of the PCL SW.