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From: Robert Jensen <bob_jensen@jhuapl.edu>
Newsgroups: comp.sys.apple2.programmer
Subject: Re: Help with 65C02 instructions
Date: 12 Jun 1996 13:20:03 GMT
Organization: JHU/APL
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References: <1996Jun12.000759.1@scvax2.shepherd.wvnet.edu> <4plsq0$sfn@blackice.winternet.com>
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X-XXDate: Wed, 12 Jun 96 13:20:42 GMT

In article <4plmkg$hou@tuba.cit.cornell.edu> Jay Krell,
jmk3@crux4.cit.cornell.edu writes:
>>   Quick answer: they're a read-modify-write between the accumulator and
>>memory. They are roughly (*) equivalent in this manner:
>
>>lda addr        lda #$80
>>ora #$80   <--> tsb addr
>>sta addr 
>
>>lda addr        lda #$7F
>>and #$7F   <--> tsb addr
>>sta addr 
>
>I think that's actually more like
> lda addr        lda #$80
> and #~$80       trb addr
> sta addr
>

I would say that you are both right, and both wrong.

The code

lda #$80
tsb addr

would translate to

lda addr
and #$80	;test the bit
php			;save the zero flag
lda addr
ora #$80	;set the bit
sta addr
plp			;recover the zero flag

and similarly

lda #$80
trb addr

would translate to

lda addr
and #$80	;test the bit
php			;save the zero flag
lda addr
and #$7f	;reset the bit
sta addr
plp			;recover the zero flag
=========================================================
Bob Jensen
bob_jensen@jhuapl.edu