A 6502 instruction that stores register A at a given memory location.
  • Function: A => N
  • Updates flags: none
  • Opcode numbers:
    (d,x) $81
    dp    $85
    abs   $8D
    (d),y $91
    d,x   $95
    a,y   $99
    a,x   $9D

You're probably wondering what happened to instruction $89. Well, it's a two-byte NOP that's faster (2 cycles) than BIT dp (3 cycles). If you're NOPping out code on older 6502s (not the CMOS parts), use $89 for all bytes except the last, which should be $EA (the normal 6502 NOP).

Similar: STX | STY
See also: 6502 instructions | 6502 addressing modes