* Notes - 6502 Instruction Set
  - 3-letter instructions
  - optional argument, value or address
  - program counter and progression
* Moving values around
  - LDA, LDX, LDY :: load a value into a register
  - STA, STX, STY :: store a value from a register to memory
  - TAX, TXA, TAY, TYA :: copy a value between registers
* Math
  - ADC :: add in accumulator, with carry bit
  - SBC :: subtract in accumulator, with carry (borrow) bit
  - SEC, CLC :: set or clear carry bit
* Bitwise operations
  - ASL :: shift accumulator left (multiply by 2)
  - LSR :: shift accumulator bits right (divide by 2)
  - ROL :: rotate accumulator bits left, wrapping carry
  - ROR :: rotate accumulator bits right, wrapping carry
  - AND :: do boolean AND in accumulator
  - ORA :: do boolean OR in accumulator
  - EOR :: do boolean exclusive OR in accumulator
  - BIT :: check if bits are set in a location
* Looping or Counting
  - INX, INY :: increment a register
  - DEX, DEY :: decrement a register
  - INC, DEC :: increment/decrement a value in memory
* Jumping
  - JMP :: jump and don't return
  - JSR :: jump and return to this spot on RTS
  - RTS :: return to the location of the last JSR
* Branch on conditions
  - CMP, CPX, CPY :: compare a register to another value
  - BEQ, BNE :: branch if equal or not-equal to zero
  - BCC, BCS :: branch if carry flag clear or set
  - BMI, BPL :: branch if minus or plus
  - BVC, BVS :: branch if overflow bit clear or set
* Stack operations
  - PHA :: Push accumulator value onto stack
  - PLA :: Pull top stack value to accumulator
  - PHP :: Push status register to stack
  - PLP :: Pull top stack value to status register
* Debugging
  - NOP :: No operation
  - BRK :: Break out of program
* Other
  - SED, CLD :: Set or clear decimal mode
  - SEI, CLI :: Set or clear interrupt mode
  - CLV :: Clear overflow bit
  - RTI :: Return from interrupt routine
  - TSX, TXS :: copy between X register and stack pointer (SP)