Re: CIA and (fast) Serial Transfer.

From: Nicolas Welte; address is valid for replies (Re:) only! (
Date: 2002-10-02 20:21:15

Michael Huth wrote:
> A related interesting fact is, that there is a 8 second copy between two 
> 1571 drives. So it seems to be possible to archieve 250kbaud with 2Mhz 
> clocked CIA (and TimerA $0002).
> So what's wrong when loading TimerA with $0001 , the CNT signal seems to 
> be ok. (btw: CNT seems to be the same signal like TimerA output at PB6 
> in toggle mode)
> Are the bit errors some chip bug?

How did you connect the two CIAs? Just a direct connection without any 
active hardware in there? Since the CNT and SP outputs have open collector 
drivers, the L to H rise time is extremely slow, typically in the range of 
one microsecond. Since the switching point is not clearly defined on the 
voltage scale, it could happen that the CNT transition is detected when the 
SP signal didn't become stable yet. You can improve this by adding a LS14 
Schmitt trigger gate before the inputs of each CIA, and inverting the 
output with a 7406. Just have a look into the 1571 schematics, it is done 
exactly this way in them!


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