Subject: Re: [stella] Meditations on the pause button|
From: "Edwin Blink" <edwin.blink@xxxxxxx>
Date: Tue, 7 Sep 2004 13:35:31 +0200
>So if I'm getting this right, I could do something like this: >lda $0f >beq this_is_a_7800 >;2600 code goes here >Unless there's some case when the 2600's data bus would not contain $0f? I like the idea. But it is possible for the 2600 to get rubbish or '0's floating on the databus too. It depends very much on the hardware pluged in and is not very reliable. That the last byte still floats on the databus has something to do with how fast a rom can change its output state and how much load there is on databus I had some problems with my dodgem hack when I burned it into a eprom. I got flashy mirrored score and super annoying sound .Because the programmer forgot a couple '#'es that caused some instructions to use whatever was floating on the databus instead of the immediate value. I also found out that when the EPROM was selected by using chip select There where more '0's on the databus.When output enable was used there was more 'rubbish'. I've also been looking on the schematic for a possible 7800 hardware detection. But found nothing concrete yet. I'm wondering though: The RIOT is addressed using the MARIA chip would there be any change on small incompatibility in the memorymap mirroring ? Memory configuration is externally locked. But MARIA seems not locked be it will some MARIA fuctions still be avialable? NMI line is controlled by MARIA chip. Is there a possibility to trigger a NMI ? BTW I wonder what dodgem would play like on a 7800. When there's always a '0'on the 7800s databus the SCORE should get the playfield color instead of player colors (NTSC/PAL) and there should be no driving sound with normal speed (PAL only).