FRAME AND SCANLINE TIMING

VDG FRAME TIMING

VDG Display Timing

Area Scanlines
Vertical Blanking 13
Top Border 25
Display 192
Bottom Border 26
Vertical Retrace 6

COCO 1/2 NTSC SCANLINE TIMING

f = 315 MHz

14MHz clock frequency is 315 / 22 1) = 14.318181818181818 MHz

FAST RATE CLOCK DIVIDER 8

Crystal clock divided by SAM fast rate clock divider (/8):
315 / 22 / 8 = 1.7897727272727273 MHz

Scale up for clock ticks per second:
315 / 22 / 8 = 1.7897727272727273

Clock ticks per frame (both fields):
315 / 22 / 8 * 1000000 / 60 = 29829.545454545456

Clock ticks per scanline (262.5 scanlines per field):
315 / 22 / 8 * 1000000 / 60 / 262.5 = 113.63636363636364

NOTE: Running a CoCo 1/2 at SAM Fast rate will cause video and RAM corruption unless a SAM Accelerator is also installed.

SLOW RATE CLOCK DIVIDER 16

Crystal clock divided by SAM slow rate clock divider (/16):
315 / 22 / 16 = 0.8948863636363636 MHz

Scale up to clock ticks per second:
315 / 22 / 16 * 1000000 = 894886.3636363636

Clock ticks per frame (both fields):
315 / 22 / 16 * 1000000 / 60 = 14914.772727272728

Clock ticks per scan line (262.5 scanlines per field):
315 / 22 / 16 * 1000000 / 60 / 262.5 = 56.81818181818182

COCO3 SCANLINE TIMING

28MHz clock frequency is 315/112) = 28.636363636363637 MHz NTSC 3)

28.4750 PAL 4)

FAST RATE CLOCK DIVIDER 16

Crystal clock divided by GIME fast rate clock divider (/16):
28.636363636363637 / 16 = 1.7897727272727273 MHz

Scale up for clock ticks per second:
28.636363636363637 / 16 * 1000000 = 1789772.7272727273

Clock ticks per field:
28.636363636363637 / 16 * 1000000 / 60 = 29829.545454545456

Clock ticks per scanline:
28.636363636363637 / 16 * 1000000 / 60 / 262 = 113.85322692574601

SLOW RATE CLOCK DIVIDER 32

Crystal clock divided by GIME slow rate clock divider (/32):
28.636363636363637 / 32 = 0.8948863636363636 MHz

Scale up for clock ticks per second:
28.636363636363637 / 32 * 1000000 = 894886.3636363636

Clock ticks per field:
28.636363636363637 / 32 * 1000000 / 60 = 14914.772727272728

Clock ticks per scanline:
28.636363636363637 / 32 * 1000000 / 60 / 262 = 56.92661346287301

MC-10 SCANLINE TIMING

NTSC clock divided by 4: 3.578545 / 4 = 0.89488625 MHz

Scale up for clock ticks per second:
3.578545 / 4 * 1000000 = 894886.25

Clock ticks per field:
3.578545 / 4 * 1000000 / 60 = 14914.770833333334

Clock ticks per scanline:
3.578545 / 4 * 1000000 / 60 / 262 = 56.926606234096695

DRAGON PAL SCANLINE TIMING

4.43361875 MHz 625 scanlines

RTS