Apple II Computer Info
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### FILE : falsereads.6502
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### Created : Sunday, January 14, 1996 Modified: Sunday, January 14, 1996
### File Type: "TEXT" File Creator: "LMAN"
### File Size: 2479 bytes 2 KB
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Newsgroups: comp.emulators.apple2,comp.sys.apple2,comp.sys.apple2.programmer
Subject: Re: 6502 false references?
Date: 22 Oct 1995 12:04:19 +1000
Organization: University of Wollongong, NSW, Australia.
Lines: 69
NNTP-Posting-Host: wraith.cs.uow.edu.au
Xref: news.uiowa.edu comp.emulators.apple2:4091 comp.sys.apple2:94056
comp.sys.apple2.programmer:5613
>>My question is: which 6502 instructions generate double references? More
>>specifically, which instructions will hit the speaker twice instead of
>>once, when applied to the speaker I/O addresses? I've looked in
>>Leventhal's and Zak's 6502 books, but didn't find this information.
From MOS Microcomputers Hardware Manual (publication number 6500-10A) Jan 1976:
ASL,CLC,CLD,CLI,CLV,DEX,DEY,INX,INY,LSR,NOP,ROL,SEC,SED,SEI,
TAX,TAY,TSX,TXA,TXS,TYA
single byte instruction
false read of following opcode
ADC,AND,BIT,CMP,CPX,CPY,EOR,LDA,LDX,LDY,ORA,SBC
indirect,x
false read of 00nn before x is added to nn
absolute,x or absolute,y
false read if page crossing occurs
zp,x or zp,y
false read of 00nn before x/y is added to nn
indirect,y
false read if page crossing occurs
STA,STX,STY
indirect,x
false read of 00nn before x is added to nn
absolute,x or absolute,y
false read
zp,x or zp,y
false read of 00nn before x/y is added to nn
indirect,y
false read
Apple II Computer Technical Information : Apple II Family Hardware Info
ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 153 of 572
(22 pages)
(16 pages)
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