     $D693/54931:   Move head one track in or out

    Jump from $D67E, $D68A:

    D693: 48        PHA
    D694: 98        TYA
    D695: A4 7F     LDY $7F         ; drive number
    D697: 99 FE 02  STA $02FE,Y

    Jump from $D69D:

    D69A: D9 FE 02  CMP $02FE,Y     ; wait for return message from
    D69D: F0 FB     BEQ $D69A
    D69F: A9 00     LDA #$00        ; disk controller
    D6A1: 99 FE 02  STA $02FE,Y
    D6A4: 68        PLA
    D6A5: 60        RTS

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