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From: jcg852@jcsneuro.uucp (John C Gallant)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Can I replace a MC74F139 IC with a 74LS139 IC??
Message-ID: <1991Mar14.034108.3380@newshost.anu.edu.au>
Date: 14 Mar 91 03:41:08 GMT
References: <1991Mar10.185521.14238@engin.umich.edu> <11260003@hplsla.HP.COM>
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tomb@hplsla.HP.COM (Tom Bruhns) writes:

>Ive gotton ahold of a number of 74LS139 chips, and I'm going to replace
>the MC74F139 with it. The difference being LS vs F.  I think LS means
>low power Shottsky, but what does F mean, and can I interchange the
>chips? Does this make them incompatable?
>----------------------

>Not incompatible, per se, but you should know that the speeds are much
>different; the F series is FAST:  Fairchild Advanced Schottky TTL or
>something like that.  LS is low power Schottky, and about half as fast,
>depending on the particular type.  (didn't bother looking up 139's for
>you.)

You can be sure that if an LS type chip would be guaranteed to work
reliably it would have been used. FAST chips are more expensive and
consume more power (I think) compared to LS chips, and they would only
be used where an LS chip won't do the job. I wouldn't substitute.

John Gallant

Centre for Resource and Environmental Studies
Australian National University

email:    jcg852@csc.anu.edu.au
fax:      +61 6 249 0757