Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!mit-eddie!media-lab!mit-caf!fritz
From: fritz@mit-caf.MIT.EDU (Frederick Herrmann)
Newsgroups: sci.electronics
Subject: Re: game arbitrator
Message-ID: <5485@mit-caf.MIT.EDU>
Date: 16 Dec 90 05:50:21 GMT
References: <34827@netnews.upenn.edu>
Reply-To: fritz@mit-caf.UUCP (Frederick Herrmann)
Organization: Microsystems Technology Laboratories, MIT
Lines: 39

In article <34827@netnews.upenn.edu> touch@dsl.cis.upenn.edu (Joe Touch) writes:
>
>
>RS-latches?  JK-flip flops?  A whole C-64?  Geez, folks, talk about
>doing things the hard way!!
>
>Here's a way thats SIMPLE, CHEAP, AND *SCALABLE* (easy to extend to an
>arbitrary number of inputs, if you balance the OR into balanced trees)
>
>		< nifty circuit deleted >
>
>Any number of D-latches can be used, provided that the OR tree is
>balanced, it will be fair.

I like your solution, but in case anyone tries to build it from your
description I'll point out that a transparent latch (e.g. 74x373) is
required.  A standard edge-triggered D-latch won't do the job.

Terminology does not seem to be that standardized.  I usually think of
a D-latch as edge triggered, but I checked a few data books on my
shelf and found that while most call the '373 a transparent latch, the
2nd edition TI TTL Data Book calls it an "Octal D-type Transparent Latch"

I've also seen transparent latches referred to as T-latches.

Hmmm... If you took the OR inputs from the input side of the latch you
could use an edge-triggered latch, but you'd need an extra feedback
term to keep late responders from retriggering it, and some way to
reset the whole thing.  The transparent solution is nicer, but if no
T-latch were available (as in many PALs), I'm sure an edge-triggered
solution could be found.

>Joe Touch
>PhD Candidate
>Dept of Computer and Information Science
>Univ of Pennsylvania

				- Frederick P. Herrmann
				  fritz@caf.mit.edu