This little instruction comes with two surprises. I’ll tell you about one: It allows us to add two binary fields without a register! We could always add two packed fields without a register, but now we can do that with 2’s complement fields in memory. You’ll have to watch the ASI video to learn the other surprise.
So, have a cup of coffee, and review this humble but interesting little instruction.
I think your description of ASI needs a bit of editing, as part of it refers to R9 being modified.
Yes… sorry.
Thanks, Andy. Too much copying and not enough editing and thought. It should be better now.
Thank you for responding so quickly! I like your descriptions with examples.
One additional one: in the third line of the description, suggest you use “the sum is stored in the Operand 1 location.” rather than “the sum is stored in the Operand 1 register.”
Oh, and it’s “Andi” rather than “Andy”
Andi, I need you as my editor! I think I’m losing it. Not only was the article incorrect, I managed to lose half the links on the main page. I had to resort to a revision. I’m not sure what errors that introduced, but I had little choice. Thanks for taking the time to point out the errors. I will try to do better. – David
Hi again, I’m trying to understand the instruction. Didn’t realize the first operand was only one byte – that’s interesting! Oh, and did you mean DH1 and DL1 in the description, instead of DH2 and DL2, as the storage area is the first operand?
Andi, I have really mucked this up for you – sorry. The first operand refers to a four-byte location in memory containing a 2’s complement value. The immediate value stored in the instruction is a one-byte 2’s complement value. The two operands are added and the sum stored in the four byte location in memory. The condition code gets set. That’s most of it. There is a companion instruction called AGSI which is similar. The difference is that the operand 1 storage location is 8 bytes in memory. Thanks for your help on this. – David
Thanks, David, for clarifying! I’m collecting your instruction descriptions as you post them – easier reference than the PoOP. Very useful!