Path: utzoo!attcan!uunet!husc6!think!ames!pasteur!ucbvax!decwrl!nsc!voder!apple!aek
From: aek@Apple.COM (Al Kossow)
Newsgroups: comp.arch
Subject: why people create write-only registers
Message-ID: <12441@apple.Apple.COM>
Date: 18 Jun 88 22:41:36 GMT
Distribution: na
Organization: Advanced Technology Group, Apple Computer, Cupertino CA
Lines: 16

In the bad old days when I did hardware, sometimes it's a real
pain to make registers readable. Take the case of a counter-chain
made up of lots of 4bit up-down counters. None of the counter outputs
were bussed together, so it was necessary to have lots of tri-state
buffers or n to 1 multiplexers going back to the data bus which would
only used to read the output values of the counters.

Sometimes when you're running tight on pcb (or chip) real-estate
you have to weigh how important it is to have lots of area tied up in
space-hogging buses just for reading a register back.


-- 
Al Kossow @ Apple Computer, Inc., Cupertino, CA
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