Do you recall my Blog of a few days ago in which I posed the question What's the minimum instruction set for a useful CPU?.
Well, according to one reader, the answer is just one instruction: Subtract and Branch if Negative (or Subtract and Branch Unless Positive)! Surely this can't be true, I thought, but he had kindly provided me a reference on Wikipedia (click this link and also check out the various web-pages linked from there).
Well, I only had a few moments to glance at this, but what I read seems to make sense. They give some examples of the types of things you can do with this instruction, and I can just about see how you can perform additions (using complement techniques). However, I'm not sure how one would go about implementing logical operations and shift/rotate instructions...
Why don’t you take a look, and if you can work it out, please email me at email@example.com and tell me how to do it! As usual, if you haven't already done so, don't forget to Sign Up for our weekly Programmable Logic DesignLine Newsletter.