nintendulato addressing modes

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nintendulato addressing modes
by mattmatteh on 2006-03-24 (#11133)
quietust, i was looking at your source and could not figure out what the difference between abx and abxw, aby and abyw, and inx and inxw are. could you explain your addressing modes ?

i have 2 swtich blocks for my cpu; the first does the addressing mode and the second does the instruction. right now i have a look up table with the cycle times and was going to put the cycle count in with the addressing mode. i read somewhere here that the cycle count is determined by the addressing mode since its the fetches that determine how long the instuction takes.

thanks

matt

by Quietust on 2006-03-24 (#11159)
The "w" addressing modes are used solely for writes, and the difference is that they will always spend an extra cycle for handling page crosses, even if they don't cross. Although it's acceptable to do a throwaway read, it is not acceptable to do a throwaway write, and the CPU doesn't know whether the 'throwaway' read is necessary until AFTER it's done.

by mattmatteh on 2006-03-29 (#11286)
thanks. i am analysing my cpu and applied almost the same idea. till now i was ignoring the extra cycles.

matt