Re: [stella] 6502 hardware register writes

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 

<< 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

Tricky problems with 2600 emulation ...... volumes 1 to 73 :)  Much easier
now the hardware is faster though.

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