Re: CIA and (fast) Serial Transfer.

From: Nicolas Welte; address is valid for replies (Re:) only! (
Date: 2002-10-03 00:10:58

groepaz wrote:
> 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)

This was my first thought as well, but then I saw that such resistors 
(3.3k) are already installed in each C64. Actually I checked this with the 
C128 schematic, but I guess the port that is not used for fast serial is 
configured the same as in the C64. Adding extra resistors does make the L 
to H transition faster, but it also adds an extra load to the CIA outputs, 
which might not do them much good.

Furthermore, the 74LS14 is not just an inverter, it cleans up slow signal 
transitions by applying a hysteresis function to them. Maybe it also has 
the advantage of having a very "low" high signal level, but this can also 
differ from LS14 to LS14. I learnt this when figuring out why the XE1541 
works with some crappy PC LPT ports with some 1541 drives, but not with 


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