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From: campbell@maynard.BSW.COM (Larry Campbell)
Newsgroups: comp.sys.ibm.pc
Subject: Re: How do you detect a V20?
Message-ID: <904@maynard.BSW.COM>
Date: Mon, 27-Apr-87 00:42:08 EDT
Article-I.D.: maynard.904
Posted: Mon Apr 27 00:42:08 1987
Date-Received: Mon, 27-Apr-87 05:40:02 EDT
References: <785@killer.UUCP> <1710@ihlpe.ATT.COM>
Reply-To: campbell@maynard.UUCP (Larry Campbell)
Organization: The Boston Software Works, Inc.
Lines: 34
Keywords: NEC V20/V30, software detection?
Summary: it's easy

In article <1710@ihlpe.ATT.COM> psfales@ihlpe.ATT.COM (Peter Fales) writes:
>In article <785@killer.UUCP>, toma@killer.UUCP (Tom Armistead) writes:
>> Is there a way to detect a NEC V20 or V30 CPU in an IBM or compatible PC
>> through software???
>
>I have an assembly language program (that came originally from netnews)
>that does exactly that.  The V20/V30 are so compatible that software
>differentiation is difficult.  The trick is to use a bug in the Intel
>chips that was fixed in the NEC chips.  ...

There's a much easier method that I got from my local NEC sales engineer.
(Why is it that computer people would rather go pawing around the networks
than just telephoning the manufacturer?)  Anyway, here's the code:

| Use undocumented Intel instruction, opcode D6, to determine if this
| is an Intel chip (D6 copies carry flag throughout AL) or an NEC V20
| (something else happens)

	xor	ax,ax		| ax <= 0
	stc			| set carry flag
	.byte	0xD6		| magic instruction
	cmpb	al,*0xFF	| which chip?
	je	cpu8088		| if FF, this is 8088
	...			| not FF, this is V20

cpu8088: ...

I don't know if this also works for the V30, but I would guess that it
does.  The NEC rep told me that on Intel chips, the test works on the
8088, 8086, 80188, and 80186.
-- 
Larry Campbell                                The Boston Software Works, Inc.
Internet: campbell@maynard.BSW.COM          120 Fulton Street, Boston MA 02109
uucp: {alliant,think,wjh12}!maynard!campbell        +1 617 367 6846