Disassembled joystick reading routine of Photon for the CoCo

joy.dasm

                  SETDP $7F
65B7: 96 57       LDA   $57
65B9: 26 51       BNE   $660C    Branch if Z = 0
65BB: 86 08       LDA   #$08
65BD: 97 57       STA   $57
65BF: 8E FF 00    LDX   #$FF00
65C2: 10 8E FF 01 LDY   #$FF01
65C6: CE FF 20    LDU   #$FF20
65C9: CC 34 0C    LDD   #$340C
65CC: 1A 40       ORCC  #$40    inhibit firq
65CE: A7 43       STA   $3,U    2nd PIA, set CB2 low. Disable Sound.
65D0: A6 C4       LDA   ,U      Read DAC
65D2: 97 56       STA   $56     store it.
65D4: E7 C4       STB   ,U      set DAC to 3
65D6: A6 84       LDA   ,X      get 1st PIA port A
65D8: 2A 33       BPL   $660D   Branch if N = 0. Branch if DAC is higher than JOY.
65DA: 86 F4       LDA   #$F4
65DC: A7 C4       STA   ,U      set DAC to 61
65DE: 86 3C       LDA   #$3C
65E0: A7 A4       STA   ,Y      1st PIA, set CA2 high. Vertical. Changes MUX in 140ns.
65E2: A6 84       LDA   ,X      get 1st PIA port A
65E4: 2B 36       BMI   $661C   Branch if N = 1. Branch if DAC is lower than JOY.
65E6: 86 20       LDA   #$20
65E8: A7 C4       STA   ,U      Set DAC to 8
65EA: 12          NOP
65EB: 12          NOP
65EC: 12          NOP
65ED: 12          NOP
65EE: A6 84       LDA   ,X
65F0: 2A 3D       BPL   $662F   Branch if N = 0. Branch if DAC is higher than JOY.
65F2: 86 E0       LDA   #$E0
65F4: A7 C4       STA   ,U      set DAC to 56
65F6: 86 34       LDA   #$34
65F8: A7 A4       STA   ,Y      1st PIA, set CA2 low. Horizontal. Changes MUX in 140ns.
65FA: A6 84       LDA   ,X
65FC: 2B 42       BMI   $6640   Branch if N = 1. Branch if DAC is lower than JOY.
65FE: 96 56       LDA   $56     retrieve stored value
6600: A7 C4       STA   ,U      set DAC to ?
6602: 86 3C       LDA   #$3C
6604: A7 43       STA   $3,U    2nd PIA, set CB2 high. Enable Sound. Changes MUX in 140ns.
6606: 1C BF       ANDCC #$BF    un-inhibit firq
6608: C6 FF       LDB   #$FF
660A: D7 56       STB   $56     $FF = don't move
660C: 39          RTS

660D: 96 56       LDA   $56     retrieve stored value
660F: A7 C4       STA   ,U      set DAC to ?
6611: 86 3C       LDA   #$3C
6613: A7 43       STA   $3,U    2nd PIA, set CB2 high. Enable Sound. Changes MUX in 140ns.
6615: 1C BF       ANDCC #$BF    un-inhibit firq
6617: C6 06       LDB   #$06
6619: D7 56       STB   $56     6 = go left
661B: 39          RTS

661C: 86 34       LDA   #$34
661E: A7 A4       STA   ,Y      1st PIA, set CA2 low. Horizontal. Changes MUX in 140ns.
6620: 96 56       LDA   $56     retrieve stored value
6622: A7 C4       STA   ,U      Set DAC to ?
6624: 86 3C       LDA   #$3C
6626: A7 43       STA   $3,U    2nd PIA, set CA2 high. Changes MUX in 140ns.
6628: 1C BF       ANDCC #$BF    un-inhibit firq
662A: C6 02       LDB   #$02
662C: D7 56       STB   $56     2 = go right (change to 4)
662E: 39          RTS

662F: 86 34       LDA   #$34
6631: A7 A4       STA   ,Y      1st PIA, set CA2 low. Horizontal. Changes MUX in 140ns.
6633: 96 56       LDA   $56     retrieve stored value
6635: A7 C4       STA   ,U      Set DAC to ?
6637: 86 3C       LDA   #$3C
6639: A7 43       STA   $3,U    2nd PIA, set CA2 high. Changes MUX in 140ns.
663B: 1C BF       ANDCC #$BF    un-inhibit firq
663D: 0F 56       CLR   $56     0 = go up (change to 2)
663F: 39          RTS

6640: 96 56       LDA   $56     retrieve stored value
6642: A7 C4       STA   ,U      set DAC to ?
6644: 86 3C       LDA   #$3C
6646: A7 43       STA   $3,U    2nd PIA, set CB2 high. Enable Sound.
6648: 1C BF       ANDCC #$BF    un-inhibit firq
664A: C6 04       LDB   #$04    4 = go down (change to 0)
664C: D7 56       STB   $56
664E: 39          RTS