dos33fsprogs/pt3_player/README.pt3_player

PT3_player


ASR = CMP #$80 / ROR


Notes:

signed 8-bit comparison
see http://6502.org/tutorials/compare_beyond.html#2.2

          SEC       ; prepare carry for SBC
          SBC NUM   ; A-NUM
          BVC LABEL ; if V is 0, N eor V = N, otherwise N eor V = N eor 1
          EOR #$80  ; A = A eor $80, and N = N eor 1
    LABEL

If the N flag is 1, then A (signed) < NUM (signed) and BMI will branch
If the N flag is 0, then A (signed) >= NUM (signed) and BPL will branch
pt3: add initial pt3_player 2019-05-07 00:16:45 +00:00			`PT3_player`

pt3: sort of have ornament/sample loading going 2019-05-12 04:14:09 +00:00

			`ASR = CMP #$80 / ROR`
pt3: fix an issue with signed 8-bit comparisons signed 8-bit comparisons are a huge pain on 6502 2019-05-13 16:33:52 +00:00


			`Notes:`

			`signed 8-bit comparison`
			`see http://6502.org/tutorials/compare_beyond.html#2.2`

			`SEC ; prepare carry for SBC`
			`SBC NUM ; A-NUM`
			`BVC LABEL ; if V is 0, N eor V = N, otherwise N eor V = N eor 1`
			`EOR #$80 ; A = A eor $80, and N = N eor 1`
			`LABEL`

			`If the N flag is 1, then A (signed) < NUM (signed) and BMI will branch`
			`If the N flag is 0, then A (signed) >= NUM (signed) and BPL will branch`