Re: CIA and (fast) Serial Transfer.

From: groepaz (
Date: 2002-10-02 22:45:29

Hello Nicolas,

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

mmmh... long ago i did the same and i _think_ getting rid of the
unstableness was as easy as adding a pullup-resistor. (i dont think i
used any inverters or sth that is)

Best regards,

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