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From: mdavis@pro-sol.cts.com (Morgan Davis)
Newsgroups: comp.sys.apple
Subject: Determining The CPU
Message-ID: <8903030216.AA29504@crash.cts.com>
Date: 3 Mar 89 01:29:07 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: pnet01!pro-sol!mdavis@nosc.mil
Organization: The Internet
Lines: 84

Here's a reprint of a message posted a while ago which shows an elegant method
of determining the type of CPU (02, C02, or 816).  It skirts around the messy
"indirect jump bug" test in a slick way by using another 6502 glitch...

CS-ID: #4627.apple/net@pro-sol 2354 chars 
Date: Thu, 19 Jan 89 18:31:40 PST
From: pnet01!crash!mcnc.org!rti!sunpix!matthew (Sun NCAA)
Subject: Re: testing for 65C02 presence

In article <8901161831.aa18496@SMOKE.BRL.MIL>, AWCTTYPA@UIAMVS.BITNET ("David A. Lyons") writes:
# >Date: Sun, 15 Jan 89 05:21:59 PST
# >From: pbhyd!ldcol@pacbell.pacbell.com
# >Subject: Re: testing all 3 parts of IIe enhancement
# 
# I wrote:
# >Also from the monitor, type
# >
# >300:A9 00 1A 00
# >300G
# >
# >You should get a register dump; I just need to know the value after
# >"A=".  It should be 00 if you have a 6502 and 01 if you have a
# >65C02.
# 
# Larry Colton asks:
# >David, can you please explain why the above works?  What is the difference
# >between the 6502 and the 65c02 as far as how the above code is treated?
# 
# On the 6502, opcode $1A doesn't do anything (anybody want to
# guarantee that? as fasr as _I_ know it doesn't); on the 65C02, $1A
# is "INC A" (or just "INC"), which adds one to the A register.
# 
# So the above program is
# 
# 300:A9 00  LDA #$00
# 302:1A     INC
# 303:00     BRK
# 
# It loads A with zero, increments it to 1 _if_ a 65C02 (or 65802, or
# 65816, for that matter) is running the code, and then Breaks into
# the monitor with a register dump.
# 
# >Larry Colton                {att,bellcore,sun,ames,pyramid}!pacbell!ldcol
# 
# --David A. Lyons              bitnet: awcttypa@uiamvs
#   DAL Systems                 CompuServe:  72177,3233
#   P.O. Box 287                GEnie mail:    D.LYONS2
#   North Liberty, IA 52317     AppleLinkPE: Dave Lyons


  David, your dealing with tricks that may, or may not hold. The best solution
I'ves scene for testing which processor is in a machine, was published in a
book by David Eyes:


	SED		;Use known bugs to determine processor type.
	LDA	#$99	;Load ACC with max BCD value.
	CLC		
	ADC	#$01	;Add one to exceed max value.
	BMI	DONE	;Bug in 6502 causes sign flag not to clear.

	CLC
	XCE		;XCE instruction is a 65C02 NOP.
	BCC	DONE	;If it was a 65816, carry would have set.
	XCE		;restore 65816 to 6502 emulation mode.
        SEC		;flag processor as 65816.
DONE	CLD		;restore processor to binary mode.
	RTS
*
* FLAG	VALUE	Processor
*
* SIGN  (minus)	6502
* SIGN  (plus)	65C02, 65816
* CARRY (clear)	65C02
* CARRY (set)	65816
-- 
Matthew Lee Stier     (919) 469-8300|
Sun Microsystems ---  RTP, NC  27560|          "Wisconsin   Escapee"
uucp: {sun, rti}!sunpix!matthew     |
------------

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