Loading...
 

RAM

The '2600 has 128 bytes of internal ram stored in the PIA chip, with it being used as both Zero-Page and stack memory. It's also the only place it's possible to use read-write instructions.

The RAM can be read and written to at $80-$FF and $180-$1FF.


The following instructions must use this internal ram to operate correctly, except when the Accumulator is being operated on.
Legal instructions:

  • DEC (Decrement)
  • INC (Increment)
  • ASL (Arithmetic Shift Left)
  • LSR (Logical Shift Right)
  • ROR (Rotate Right)
  • ROL (Rotate Left)

Illegal instructions:

  • DCP (Decrement & Compare)
  • ISC (Increment & Subtract With Carry)
  • SLO (Arithmetic Shift Left & OR)
  • SRE (Logical Shift Right & EOR)
  • RRA (Rotate Right & Add With Carry)
  • RLA (Rotate Left & AND)