SLC 1k or 4k Instructions

How many lines of code can you put into a SLC 5/01 with 1k ro 4k of Instructions?

1747-L511 CPU and the 1747-L514 CPU

This is for a small stand alone machine with 32 points of input and 16 points of output. No communications cards. Fairly simple algorithm of if this input is on do this output etc...

Hard question to answer. Using branching, it is possible to use all the memory in one rung. Here is a link to the SLC500 Instruction Set Reference. Go to page C-2 and it summarizes how much memory the different instructions consume.

SLC500 Instruction Set Reference Online Manual from AB web site

Figure at minimum one XIC and one OTE uses 1.75 words of memory. You can take it from there.

Good Luck!

OG

It sounds like you are trying to figure out which PLC to buy (less memory = less money), but want to get the right one (avoid restocking fees).

If you aren't pressed for time, and if the lead time on either processor isn't too severe, just write the program in RSLogix (or AI) before you purchase. When you verify, the software will check if memory has been exceeded. You can easily change processor types in the software from one to the other (unlike with a Panelview, for example) if you guessed wrong.

You can do the memory count addition game, but I've found it's faster and more accurate just to write the code and see how much memory is used.

General rule of thumb for memory usage: One word for each instruction, plus one word for each address referenced by the instruction. Rungs count as 2 instruction (SOR, EOR) and branches two plus one for each branch down (BST, BND, NXB).
(This is from someone who once had to replace MOV 0 instructions with CLR instructions (or better, FFL) to squeeze a few extra words out of badly written program.)

Operaghost said:

Hard question to answer. Using branching, it is possible to use all the memory in one rung. Here is a link to the SLC500 Instruction Set Reference. Go to page C-2 and it summarizes how much memory the different instructions consume.

SLC500 Instruction Set Reference Online Manual from AB web site

Figure at minimum one XIC and one OTE uses 1.75 words of memory. You can take it from there.

Good Luck!

OG

Click to expand...

You did a good job answering that question as that manual has all the info I need to figure it out.

Thanks

And more good advice to add to the other quote

Thanks

Allen Nelson said:

It sounds like you are trying to figure out which PLC to buy (less memory = less money), but want to get the right one (avoid restocking fees).

If you aren't pressed for time, and if the lead time on either processor isn't too severe, just write the program in RSLogix (or AI) before you purchase. When you verify, the software will check if memory has been exceeded. You can easily change processor types in the software from one to the other (unlike with a Panelview, for example) if you guessed wrong.

You can do the memory count addition game, but I've found it's faster and more accurate just to write the code and see how much memory is used.

General rule of thumb for memory usage: One word for each instruction, plus one word for each address referenced by the instruction. Rungs count as 2 instruction (SOR, EOR) and branches two plus one for each branch down (BST, BND, NXB).
(This is from someone who once had to replace MOV 0 instructions with CLR instructions (or better, FFL) to squeeze a few extra words out of badly written program.)

Click to expand...