[Coco] Raster position

[Torsten Dittel]

> On most or all versions of the Coco1, using the full fast poke caused a
> loss of video. I'm not sure if that carried over to the Coco2.

No difference between CoCo1 and CoCo2 regarding this item.

Actually, loss of video was only one aspect - AFAIR the RAM wasn't refreshed
appropriately in the
"double speed" mode (POKE65497,0?), so the CoCo lost data and would hang up
after some time.

There was a trick to periodically go back to "single speed"
mode for a short time (e.g. within the VSYNC (50/60Hz) interrupt service
routine) to allow the memory refresh. I remember that music player published in
the RAINBOW (Bells&Whistles2?) did that and played "Axel F" with improved
quality but messed video on a CoCo1/2. 

> However, there is a
> half-fast poke which is address dependent for speed and code in RAM is fast
> while code in ROM is slow. Video works in this mode.


I remember that vice versa (POKE65495,0?): code executed in RAM was single
speed, while code from ROM was 1.5x speed. It made BASIC run faster if not in
all RAM mode. Disk, tape & printer (via bit-banger port) access was messed and
SOUND and PLAY changed frequency and velocity as well.

The mode was easy to
recognize, because the chamelon cursor was flashing faster too.

Regards,
Torsten