Re: [stella] What I've got so far

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/

Current Thread