Extra Instructions of the 65XX Series CPU

Summary

"Extra Instructions Of The 65XX Series CPU" By: Adam Vardy (abe0084@infonet.st-johns.nf.ca) [File created: 22, Aug. 1995... 27, Sept. 1996] The following is a list of 65XX/85XX extra opcodes. The operation codes for the 6502 CPU fit in a single byte; out of 256 possible combinations, only 151 are "legal." This text describes the other 256-151= 105 operation codes. These opcodes are not generally recognized as part of the 6502 instruction set. They are also referred to as undefined opcodes or undocumented opcodes or non-standard opcodes or unofficial opcodes. In "The Commodore 64 Programmer's Reference Guide" their hexadecimal values are simply marked as future expansion. This list of opcodes was compiled with help from "The Complete Inner Space Anthology" by Karl J. H. Hildon. I have marked off the beginning of the description of each opcode with a few asterisks. At times, I also included an alternate name in parenthesis. All opcode values are given in hexadecimal. These hexadecimal values are listed immediately to the right of any sample code. The lowercase letters found in these examples represent the hex digits that you must provide as the instruction's immediate byte value or as the instruction's destination or source address. Thus immediate values and zero page addresses are referred to as 'ab'. For absolute addressing mode the two bytes of an absolute address are referred to as 'cd' and 'ab'. Execution times for all opcodes are given alongside to the very right of any sample code. A number of the opcodes described here combine the operation of two regular 6502 instructions. You can refer to a book on the 6502 instruction set for more information, such as which flags a particular instruction affects. ASO *** (SLO) This opcode ASLs the contents of a memory location and then ORs the result with the accumulator. Supported modes: ASO abcd ;0F cd ab ;No. Cycles= 6 ASO abcd,X ;1F cd ab ; 7 ASO abcd,Y ;1B cd ab ; 7 ASO ab ;07 ab ; 5 ASO ab,X ;17 ab ; 6 ASO (ab,X) ;03 ...