TI PM550 Questions

Anyone remember programming a TI PM550? Or have an old manual?

I am tasked with replacing such a unit and have a ladder logic listing of the program without any comments or address descriptions. I have a few questions:

What is the memory arrangment? I have identified V, C, CR, X, Y and A data types. I'm currently guessing that V is integer variable, C is integer constant, CR internal bit, X discrete input, Y discrete output and A is an analog input? Any comments?

The counter and timer blocks have two input branches, is one an enable and the other a reset?

Some timer blocks are just TMR and others are TMRP, all of the counters are CTRP, what is the P for? Edge active instead of level active?

How were the PID loops implemented? Series or parallel P,I, D terms, maybe a true ISA implementation? What is "variable tune" and "loop status flag"...

Any help would be greatly appreciated

Wow, now there's a trip down Memory Lane!

Your identification of the memory areas is pretty much correct as I remember it. Beware the Vs and Cs however. These were not purely integer. Although each address was a 16-bit register, you could also use two consecutive addresses to hold floating-point 32-bit variables. And the difference was subtle until you got used to it. V100 is a 16-bit register, V100. is a 32-bit reference which uses the area normally occupied by V100 and V101 - the '.' is the significant thing. I think you could also mix integer and FP arithmetic quite freely e.g. V200. := V100 x V18. + V1

The input branches on TMRs and CTRs were used as -
top (first) branch (TMR) : run/hold
top (first) branch (CTR) : event (rising edge triggered)
bottom (second) branch (TMR & CTR) : enable when true, reset when false.

P suffixes on a TMR or CTR meant they were 'P'rotected - you couldn't alter them using any form of operator interface. Unprotected TMRs and CTRS could have their presets or current values adjusted at runtime.

I can't remember if I ever knew the theory behind the PM550 loops. You just filled in the configuration table and they worked! Life was so much simpler all these years ago. 'Variable tune'? Nope, forgotten that one as well. 'Loop status flag' I seem to recall was an area of bit memory (16 of them in a single word?) each of which were used to indicate certain aspects of the loop's operation - manual, automatic, cascade, in hi-alarm, in lo-alarm, in hi-hi-alarm etc. Damned if I know which ones did which!

Sorry Madkins, it may not help you much, but it did me good to blow some dust off these old neurons.

Regards

Ken