3 ms·
Only in a vague sense. The 256 byte window can't be relocated. Most instructions (boolean and ALU) only leave results in the accumulator, not RAM. (Inc/dec a
by chillingeffect 9y ago
Only in a vague sense. The 256 byte window can't be relocated. Most instructions (boolean and ALU) only leave results in the accumulator, not RAM. (Inc/dec are an exception, but very slow). Internal registers are used to index zero page bc it can't index itself. Direct, arbitrary access to 16 bit address space is also possible without updating a memory pointer via additional write instruction. (The zero page is basically a parallel set of instructions with eight zeros in the upper 8 bits off address).
- jacquesm 9y ago> The 256 byte window can't be relocated. That's true, but that doesn't change the principle. Other processors (like the 6809 for instance) used the same model and could relocate the 'zero' page. > Most instructions (boolean and ALU) only leave results in the accumulator, not RAM. Yes, but that's the way this is supposed to work. A, X and Y are scratch with the real results held in 'quick access' zero page variables. > (The zero page is basically a parallel set of instructions with eight zeros in the upper 8 bits off address). Yes, and this was explicitly designed in such a way to offset the rather limited register file of the CPU. In the 6809 it was called the 'direct' page, and in that form it was a lot more usable since you could do a complete context switch with a single load (which the 6809 operating system OS/9 used to good effect).