The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
awemawson:
Theoretically to a file, but I'm having difficulty deciding if it actually has :scratch:
I have the .pdf version of a manual for STEP5 V7.0 but mine is V7.23 - probably much the same apart from details. I've given up scrolling up and down screens cross referencing stuff in the manual, and knuckled down and printed it out this afternoon. Only 513 pages or an entire ream of A4 paper !
I find it much easier with a paper manual that I can stick Post-It notes on to temporarily mark my passage through the jungle.
One issue is that all the documents I've found so far start off getting you to construct the logic of a program, program it and upload it, but include very little about the reverse process starting from an existing but undocumented program already in a PLC !
But applying PK's poster regarding persistence (which I've printed out!), we'll get there eventually or I'll !now the reason why not!
PekkaNF:
--- Quote from: awemawson on October 11, 2018, 11:01:40 AM ---.....
One issue is that all the documents I've found so far start off getting you to construct the logic of a program, program it and upload it, but include very little about the reverse process starting from an existing but undocumented program already in a PLC !
....
--- End quote ---
Because trying to make sense of BU is very hard.
99.99% professionals have source code and then try fiqure out what has been changed in the code on PLC and when circuit has been found zoom in to FB/PB "What it does and why"?
To get there you use compare -function and cross reference of I/O, but hard to do if you don't have commented source code.
If I had to do it I would find the outputs that drive the tool cahnger (if that had a problem). Cross reference the outputs one at the time, then find the blocks that drive those outputs and then check which inputs make up the logic.
Trying to understand the whole big tamale is a big project.
Pekka
awemawson:
Oh yes Pekka, unless I'm VERY lucky this is definitely gong to be a long haul now I have my teeth into it.
A bit more poking about confirms that I have managed to download three 'blocks' from the PLC and can examine them and potentially edit my local copy. I don't think I can modify the code in the 820T PLC yet as A/ some is in EPROM and B/ the rest (all 18K of it) is at this point sacrosanct until I undersatand it better.
OK what have I got? Well I have 'OB 2' - (organization block #2) which is quite short having only a few lines and is apparently the interrupt service routine for high priority interrupts, but VERY interestingly refers to the 'W-Axis' in plain text, conditionally calling up 'FB 99' to service this interrupt. And FB 99 also refers in plain text to the W-Axis.
Why all the excitement about the W-Axis when this lathe hasn't got that option? Well it's not the axis that gets me excited, but that fact that some of the code obviously includes plain text giving a clue as to its function, which will help enormously.
As an aside I'm sure that I've read in one of the commissioning guides for the 'GEN2' lathes (mine is 'GEN1') that the commissioning Engineer was instructed to run a program that examined the options required by the particular customer, and create the PLC program by assembling blocks, so I assume that blocks are enabled or disabled in fact from the W-Axis one I've found.
Having now printed the documentation I've decided to 'start over' with the set up of the file structure on STEP5 to isolate my 'project' from the various examples etc, and thus get a clearer idea of what is stored where.
PekkaNF:
Looks vaquelly familiar.
OB 1 "Cyclic" calls PB:s (ladder)
OB 2 is intterrupts, you don't want to saturate this file with may simultaneous calls
OB 10-18 calls programs on certain time base, we used them on FB:st that had exacting time requiremets like counters, positioners, servos etc.
OB31 "cyle time monitor" is a lot of fun if your CPU gets loaded! It is really easy to exceed cycle time if you have too much junk on too fast loop.
You know these OB calls? p. 97
https://cache.industry.siemens.com/dl/files/150/1086150/att_1992/v1/948then.pdf
And one thing to know that there are two flags set and used routinely trought the program to enable/disable piece of code "permanently":
"FALSE" in case of M0.0
"TRUE" in case of M0.1
Just in case you wonder what these are.
pekka
awemawson:
Thanks for that Pekka, that's a useful document that I will add to my reading list !
I have a rather bad photocopy scan in pdf format of a Siemens guide to programming this particular PLC - I'm trying in vain to find a better copy that is in 'pdf searchable' format rather than just images. It's this document if you happen to have a source:
6Zb5-410-0BX02-0BA0 (or 0BA1)
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