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From: tim@cmu-cs-k.ARPA (Tim Maroney)
Newsgroups: net.micro
Subject: Re: 8086 et al status bits question.
Message-ID: <20980037@cmu-cs-k.ARPA>
Date: Thu, 20-Dec-84 17:17:23 EST
Article-I.D.: cmu-cs-k.20980037
Posted: Thu Dec 20 17:17:23 1984
Date-Received: Sun, 23-Dec-84 01:11:15 EST
References: <12@spar.UUCP>
Organization: Carnegie-Mellon University, CS/RI
Lines: 30

Of course it is useful to set/clear the Z status bit in the 8080 on a DEC
instruction!  Loops that count down to zero are much easier.  Exemplia
gratia:

	mvi	b,limit
loop:
	; whatever the loop does
	dec	b
	jnz	loop

I wish they had done the same with DCX instructions, so you could count down
using 16-bit integers, but no, you have to go:

	lxi	b,limit16
loop:
	; whatever
	dcx	b
	mov	a,b
	ora	c
	jnz	loop

which is grodier to the nth degree.
-=-
Tim Maroney, Carnegie-Mellon University Computation Center
ARPA:	Tim.Maroney@CMU-CS-K	uucp:	seismo!cmu-cs-k!tim
CompuServe:	74176,1360	audio:	shout "Hey, Tim!"

"Remember all ye that existence is pure joy; that all the sorrows are
but as shadows; they pass & are done; but there is that which remains."
Liber AL, II:9.