[Diy_efi] Re: Diy_efi Digest, Vol 6, Issue 24

[Larry Ing]

Hi Jeff,

I was reading your post on the CMOS logic and you don't have it quite 
correct.  The logic thresholds for CMOS is 10% and 70% of the supply rails, 
not 50%.  That implies that with a 5v supply, the '0' potential is 0.5v and 
the '1' potential is 3.5 volts.

Furthermore, TTL should 'nearly never' have a problem driving CMOS.  The 
thresholds that you speak of are only relevant if you are driving many 
logic loads to the point of loading any particular output down.  Then and 
only then do you have to worry about fan-in/fan-out of any particular 
TTL/CMOS device.

BTW, what is the project and what are you and your friend trying to accomplish?

Larry


At 12:00 PM 6/17/2003, you wrote:
> > Jeff wrote:
> > > ... has quite different '0' and '1' thresholds.
> > Try driving
> > > it with HC family logic, TTL won't work.
> >
> > TTL can work. "classic" CMOS has a logic threshold
> > at one half
> > of the power supply, if the supply is 5V then the
> > threshold is
> > 2.5V. "classic" TTL has a minimum logic high output
> > of 2.4V,



Larry Ing
N6XZD
PGP on request

Larry Ing
N6XZD
PGP on request



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