I have to convert (re-write) some logic from a printout of the ladder. The new PLC will be Allen Bradley (no problem there). I believe the old PLC was a TI because "X" is used as an input, "Y" is an output, "V" is variable memory, etc.

However, there is an instruction that I don't recognize... The rung has an open contact with address "SP1". This open contact leads to a stack of blocks on the rung output. The first block is "LD" with address "VC40", next is "OUT" with address "V200", then LD VC80, then OUT V2001.

Can anyone give me some help on this rung?

 

It appears your old PLC is of the Koyo variety. SP1 is a special "Always On" coil. VC40 is the word memory alias for discrete bits C40-C57. The rung is moving bits C50-C57 in a word form into v-memory location "V200", and also moves C80-C97 to V2001.

Hope that helps

 

That's from one of the small TIs that's very accumulator-centric, either the 305 or 405 series. The Automation Direct PLCs have the same instruction set.

"LD" means to load the accumulator with the value from the specified address. OUT means to transfer the value in the accumulator to the address given. So this rung in AB-speak would be SOR XIC SP1 BST MOV VC40 V200 NXB MOV VC80 V2001 BND EOR.

These PLCs, like ABs, can refer to relay ranges a word at a time (like B3:0 will get B3/0 through B3/15), so VC40 is just the 16 bit word representing relays C40 thorugh C57. (Addresses are octal in these PLC's.)

The "SP" relays are internally set status relays like always on, always off, various periodic flasher bits, battery status, etc. SP1 is always on so your AB equivalent could even remove the SP1 contact (and change the two MOVs to a COP), for SOR COP #B3:0 #N7:0 2 EOR.
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Steve Myres, PE
Automation Solutions
(480) 813-1145