Subject: Re: [stella] 6502 hardware register writes From: AutismUK@xxxxxxx Date: Fri, 2 Nov 2001 08:28:48 EST |
In a message dated 02/11/01 8:57:28 GMT Standard Time, adavie@xxxxxxxxxxxxx writes: << Being somewhat interested in working on a '2600 emulator, I thought I'd start by asking if writes to hardware (ie: graphics) registers occur on the last cycle of the instruction. That is, in, say, a 3-cycle store, does the effect of writing to the register become visible on the first pixel immediately drawn after the end of the 3rd cycle? Or is it apparent at the start of the 3rd cycle (ie: end of 2nd cycle)? In general, I'm interested in discussing '2600 emulation - perhaps those on the list who have tackled this, and can help when tricky problems show up, might hold up their hands. >> I think they occur on the last cycle, but it probably doesn't matter because almost all the syncing is done by sta (something) anyway. It could be problematical if for some reason you wanted to use inc or dec to do a write. Tricky problems with 2600 emulation ...... volumes 1 to 73 :) Much easier now the hardware is faster though. ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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