passport/src/slots.a

DiskIIArray
         !byte 00,00,00,00,00,00,00

;-------------------------------
; ScanForDiskII
; scan all slots for things that
; look like Disk II cards
;
; out: all registers clobbered
;      all flags clobbered
;      DiskIIArray filled with 00 or FF
;-------------------------------
!zone {
ScanForDiskII
         lda   #$00
         sta   cmp1
         ldx   #$07
.fingerprint
         txa
         ora   #$C0
         sta   cmp1+1
         ldy   #$01
         lda   (cmp1),y
         cmp   #$20
         bne   .next
         ldy   #$03
         lda   (cmp1),y
         bne   .next
         ldy   #$05
         lda   (cmp1),y
         cmp   #$03
         bne   .next
         ldy   #$FF
         lda   (cmp1),y
         bne   .next
         tya
         sta   DiskIIArray-1,x
.next
         dex
         bne   .fingerprint
         rts
}

;-------------------------------
; NextSlot
;-------------------------------
!zone {
NextSlot
         lda   DRIVE
         cmp   #$31
         bne   .incslot
         lda   #$32
         sta   DRIVE
         bne   .done      ; unconditional branch
.incslot
         lda   #$31
         sta   DRIVE
         inc   SLOT
         lda   SLOT
         cmp   #$38
         bne   .nowrap
         lda   #$31
         sta   SLOT
.nowrap
         sec
         sbc   #$30
         tax
         lda   DiskIIArray-1,x
         beq   .incslot
.done
         lda   SLOT
         cmp   #$36
         bne   .reallydone
         lda   #$32
         sta   DRIVE
.reallydone
         rts
}