Subject: Re: [stella] What I've got so far From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney) Date: Fri, 09 Jul 1999 01:00:47 GMT |
>> So by even taking a number from, say, $FCCC and copying it to the X >> register, that will set the zero flag? > >only if $FCCC is zero will that set the zero flag. Exactly. Any load instruction (LDA, LDX, LDY) set the zero flag if the value loaded into the register is zero. >> Is it possible to compare, say, $FCCC and $F281 directly without >> transfering numbers to the X and Y registers? > >you would have to send at least one of those numbers to >either the accumulator or the X or Y registers in order >to compare the other number. you cannot compare two >numbers without putting at least one in the accumulator >or X or Y. note also that you cannot compare numbers in two registers; it has to be either a register and an immediate (CMP #192) or a register and memory. >im not sure, but i think the three lines of VSYNC are also part >of vertical blank, its just that the VSYNC signal is there for >3 lines to synchronize the vertical output with the top of the >frame...and vertical blank is there for at least 37 lines to >physically turn off the electron beam. its my understanding >that some games turn on VBLANK at the same time VSYNC is turned on >but again, i dont know the specifics. so please, dont quote me >on this. Most games turn on VBLANK at the start of the overscan period (soon as the frame is done being drawn), and leave it on through the VSYNC period. -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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