[Coco] TEAC FD55-E speed adjustment

Robert Gault robert.gault at worldnet.att.net
Tue Feb 14 00:14:10 EST 2006

Oops, the PAL formula should be CM=60*CLOCK*889843.8. The 60 will not 
change as that is the seconds to minutes conversion.

Robert Gault wrote:
> The ml program turns off the interrupts and then sends a forced 
> interrupt to the drive which is on. This will prevent the drive from 
> timing out and no command will be in progress. It then monitors the 
> controller status register $FF48 checking for the index bit. Once an 
> index hole is found, it counts the number of CPU cycles until the next 
> index hole is seen. The cycle count is returned to the main Basic program.
> The main program can be adjusted for CPU clock speed of 1 or 2MHz. It 
> can also be adjusted for cycles per minute: 
> CM=60*CLOCK*894886.3:'CYCLES/MIN.
> That means it should be easy to adjust CM for a PAL Coco which I think 
> would use 50 & 889843.8. That assumes a PAL Coco divides the master 
> crystal by 32 to get the slow CPU clock speed as does a US Coco. In any 
> case some suitable factor can be found.
> Bob Devries wrote:
>> Robert,
>> How does your programme keep its timing correct? If it uses the HS or 
>> FS interrupt from the PIA, then it will not be accurate on the PAL 
>> colour computer.
>> -- 

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