[Coco] POKE 65495,0

[Robert Gault]

Diego Barizo wrote:
> According to a text in 
> http://www.old-computers.com/museum/computer.asp?st=1&c=508
> the double speed poke did not really switch the machine to 1.8 MHz.
> 
> That doesn't seem right... or is it?
> 
> Diego
> 
> 
The statement is partially true and partially false. There are two 
double speed switches on a Coco1 or Coco2, $FFD6/$FFD7 $FFD8/$FFD9. The 
first lets ROM access occur at 2MHz but RAM (user programs) stays at 
1MHz. This switch does not exist on the Coco3. The second runs all 
memory at 2MHz.

The article claims, "Also if you were using the upper 32k of ram, the 
double speed poke would wipe the memory." which is wrong. I ran some of 
my ml programs using the $FFD9 switch which ran both RAM and ROM at 
2MHz. Video was lost during this period but immediately returned to 
normal when the clock rate was slowed. So RAM was not wiped.