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From: logajan@ns.network.com (John Logajan)
Newsgroups: sci.electronics
Subject: Re: A 74F74?
Message-ID: <1990Apr10.225733.27152@ns.network.com>
Date: 10 Apr 90 22:57:33 GMT
References: <9561@sdcc6.ucsd.edu> <37746@mips.mips.COM> <1990Apr8.000826.16803@utzoo.uucp> <1990Apr8.061809.6501@ns.network.com> <29798@amdcad.AMD.COM>
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phil@pepsi.AMD.COM (Phil Ngai) writes:
>I haven't used 74FC but I have used 74AC parts and in my experience,
>the 74AC parts are much worse than any other TTL compatible parts,
>including the F series, in requiring line termination.
>
>Are FC parts better? What is the difference between FC and AC?

The FC parts are different from the AC parts in that there is no such
thing as FC parts :-)   SORRY, I meant to say AC and ACT parts are the
designations for F.A.C.T. (Fairchild Advanced CMOS Technology.)

ACT parts have TTL compatible input circuits, whereas AC parts need CMOS
levels.  Both ACT and AC outputs swing the full CMOS range, which certainly
would seem to imply a greater need for termination in high speed use.

AC/ACT parts run with supply voltages from 2 to 6 volts, use 1/10th of
the power of FAST or ALS, and 1/20th the power of LS (under 1 Mhz.) 
AC/ACT also has good noise immunity 1.25v/1.25v and can source or sink
24 ma.

Maximun propagation delay  FAST vs FACT  (ACT.  AC's are slightly slower.)

74F374 (8 bit F/F) vs 74ACT374
 10ns                   11.5ns

74F00 (nand) vs 74ACT00
 6ns              9.5ns

FACT parts sure look good on paper.

-- 
- John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428
- logajan@ns.network.com, john@logajan.mn.org, 612-424-4888, Fax 424-2853