Looking for help with Brown Boveri code

JNielson

Member
Join Date
Jan 2006
Location
Salem, WI
Posts
3
I have an old (mid 1980's) BBC PLC that I'm replacing with an AB. I have the print out from the customer for the PLC but there is some code I don't understand.


| M 03,00 M 03,00
|---] [----------------------+----(/)----
| |
| + MA
Contiunes like this for 10 rungs with the last one like this:
|
| M 03,09 M 03,09
|---] [----------------------+----(/)----
| |
| + MA
|
ME|



I'm thinking this is something like a MCR zone but I hope someone can tell me for sure.

Thanks
 
Last edited:
Those are inverted outputs that clear any of the bits if they are set. I guessing that the MA instruction is equivalent to a JMP (GOTO instruction) or possibly a surbourine call or return instruction. I noticed you included an ME label to the side of the ladder. Is there an MA label elsewhere along the left rail? If so then I would guess that this is most likely the equivalent of a JMP instruction. It could however be functioning as a subroutine return or call.

Keep in mind that in many older PLCs (and even some new ones) even though they had subroutine calls the ladder was still one monolithic structure without seperate files, like the old BASIC programs with GOTO and GOSUB calls.
 
Last edited:
In looking closer and including the left rung info:



S0078| M 03,00 M 03,00
0262|---] [----------------------+----(/)----
| |
| + MA

     |
MA |
|
S0079| M 03,01 M 03,01
0265|---] [----------------------+----(/)----
| |
| + MA
|
MA |
|

Contiunes like this until the last two look like this:

S0084| M 03,06 M 03,06
0280|---] [----------------------+----(/)----
| |
| + MA
|
MA |
|
S0085| M 03,07 M 03,07
0283|---] [----------------------+----(/)----
|
|
ME |
|
S0086|
0286|---| |--- normal ladder stuff



The program has five sets mostly like above. The one set is different in that it has set and reset bits on the output rail. With a MA at the rung output position and along the left rail then a ME at the left rail, like above, with 8 rungs in between.

I don't think it's a sub-routine type function. Could be a jump but I would like to make sure.

Thanks
 
We have a number of machines running on the older (mid 1980's) PLC's, namely ABB S, S+ and T300 series.
ALARIC is correct - all Binary Flags ( M ) that are 1 are reset to zero and then a jump is made to MA...
MA is the Label identifier, these are labeled with a number - MA number (from 0 ... 999).
These are used as branch instructions with SPRUNG (conditional jump to a label) and LZB (run number block).
I can't figure out the ME instruction as yet.
 
Thanks for the reply, the MA as a label ID I'm not sure of as none of the ones on the print out have a number associated with them. Each of the MA's on the output are followed by a MA to the left of the power rail, normally on the next rung, until you get to the ME. The ME seems to be the an 'end' statement. I do have one exception to the above as I mentioned in my last note.
 

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