[Coco] TEAC FD55-E speed adjustment

Robert Gault robert.gault at worldnet.att.net
Tue Feb 14 00:06:19 EST 2006

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.
> -- 

More information about the Coco mailing list