EAF block in PLC-2

[Guest Jupho]

I'm slightly confused on the difference between the "execute auxillary function" operations and the regular math operations. The PLC-2/05 manual wasn't much help. Can anyone explain it to me?

[Gerry 13]

The PLC2's only do basic 4-function math on 3-digit BCD numbers. The 2/15, 2/16, 2/17, 2/05 can have an optional 'EAF' PROM installed to give additional functions. From memory there are 3 or 4 different PROM's, but you can only install one. One might provide a PID function, another might provide trigonometric functions, etc. The functions are called using the EAF instruction. I think that there are separate manuals for each type of EAF PROM.

[Guest Jupho]

The PLC-2/05 programming manual mentions using the EAF command. It tells me it does the four basic operations. However, I'm confused as to why one would use that versus the regular commands --(+)-- and such. As always, thanks for your help.

[Gerry 13]

As I said, the PLC2 works with 3-digit numbers. If you have the -AF1 or -AF4 EPROM installed, you can do math with 6-digit numbers using the EAF functions. The -AF4 includes logarithms, powers, square root, and trig. The -AF3 EPROM adds file search and diagnostic functions similar to the 2/30. I thought there was also an EPROM supporting PID but I can't find any documentation for it. Look under PLC2 on the A-B Manuals page for docs.

[Guest Jupho]

Also, the PLC-2 works with only the lower 12 digits of a word, right? So if I have a word whose value is 0000 0001 0010 0011 , the 0011 isn't used in any (regular) addition, subtraction, etc. operations?

[Gerry 13]

No. Bits are numbered 0 to 17 (octal), right to left. For your example, the value the PLC2 sees is 123 (decimal). In math operations, the upper 4 bits (14-17 octal) reflect status - e.g. carry/overflow/borrow.

[Guest Jupho]

Alright, I see now. Thanks for your help.