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(Atari 130xe) Cycling question


Darkhog

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How many cycles does Atari perform in one "frame" (time between changes to RTCLOK)? I'd like to know values for both NTSC and PAL. I need to know it to time my music routines properly.

1/60 second for NTSC. Probably 1/50 second for PAL. It is called a 'jiffy' and 8000 'machine cycles' can be performed in a jiffy. This is from 'Mapping the Atari' location 18,19,20 ($12,$13,$14)

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  • PAL - 35568 cycles
  • NTSC - 29868 cycles

Yes. The two has always same 114cycles per scanline happening each frame 50 or 60 times each second.

Then it's up to each T.V. Type:

NTSC: 114cycles x 262scanlines

PAL: 114cycles x 312scanlines

 

To this available you have to discount your coding instructions and the screen GR. Mode and if 32, 40 or 48Bytes wide but also the number of scanlines you have with something shown on screen (for example: if just playing music and all screen scanlines are Blank/not used then the screen display takes no cycles. That's why why greatest A8 pieces of music just play on an empty/black screen).

 

 

Am I right?

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Blank screen music quality relates to digital sample playback - it can be done in active screen but timing is better on blank.

 

Generally for chiptune stuff you just use the VBlank NMI which will always be ~ 50/60 Hz. A cheap way to maintain constant tempo is to develop the music as if destined for Pal. Then if NTSC is detected, skip the play routine every 6th frame. Timing will be slightly out but hardly detectable and tempo will be near exact on both systems.

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