diff --git a/src/hw.diskii.a b/src/hw.diskii.a
new file mode 100644
index 0000000..f24caf6
--- /dev/null
+++ b/src/hw.diskii.a
@@ -0,0 +1,36 @@
+;-------------------------------
+; ScanForDiskII
+; scan all slots for things that look like Disk II cards
+;
+; in:    X = 0
+;        Y = 0
+; out:   DiskIIArray populated
+;        X = 0
+;        all other registers and flags clobbered
+;-------------------------------
+!macro ScanForDiskII {
+         ;X=0,Y=0
+         stx   cmp1
+         ldx   #$07
+-        txa
+         ora   #$C0
+         sta   cmp1+1
+         ldy   #$01
+         lda   (cmp1), y
+         cmp   #$20
+         bne   +
+         ldy   #$03
+         lda   (cmp1), y
+         bne   +
+         ldy   #$05
+         lda   (cmp1), y
+         cmp   #$03
+         bne   +
+         ldy   #$FF
+         lda   (cmp1), y
+         bne   +
+         tya
+         sta   DiskIIArray-1, x
++        dex
+         bne   -
+}
diff --git a/src/initscan.a b/src/hw.harddisk.a
similarity index 84%
rename from src/initscan.a
rename to src/hw.harddisk.a
index a25595a..d994d31 100644
--- a/src/initscan.a
+++ b/src/hw.harddisk.a
@@ -4,53 +4,17 @@ SlashRAM_e
 RAMFileName    !raw "PASSPORTTMP.DSK"
 RAMFileName_e
 
-;-------------------------------
-; ScanForDiskII
-; scan all slots for things that look like Disk II cards
-;
-; in:    none
-; out:   DiskIIArray populated
-;        all registers and flags clobbered
-;-------------------------------
-ScanForDiskII
-         lda   #$00
-         sta   cmp1
-         ldx   #$07
--        txa
-         ora   #$C0
-         sta   cmp1+1
-         ldy   #$01
-         lda   (cmp1), y
-         cmp   #$20
-         bne   +
-         ldy   #$03
-         lda   (cmp1), y
-         bne   +
-         ldy   #$05
-         lda   (cmp1), y
-         cmp   #$03
-         bne   +
-         ldy   #$FF
-         lda   (cmp1), y
-         bne   +
-         tya
-         sta   DiskIIArray-1, x
-+        dex
-         bne   -
-         rts
-
 ;-------------------------------
 ; ScanForRAMAndHardDisks
 ; scan all slots for things that look like RAM disks or hard drives
 ;
-; in:    none
+; in:    X=0
 ; out:   HardDriveArray populated
 ;        RAMDiskImagePath possibly populated (if a suitable RAM disk was found)
 ;        all registers and flags clobbered
 ;-------------------------------
 ScanForRAMAndHardDisks
-         lda   #$00
-         sta   iunit
+         stx   iunit
 @nextunit
          lda   iunit
          clc
diff --git a/src/wrapper.a b/src/wrapper.a
index 8139081..128fbd8 100644
--- a/src/wrapper.a
+++ b/src/wrapper.a
@@ -6,6 +6,7 @@
          !source "apidefs.a"
          !source "strings/enid.a"
          !source "prefs.load.a"
+         !source "hw.diskii.a"
          !source "../build/vars.a"
 
          bit   $C082                 ; read ROM, no write
@@ -42,12 +43,13 @@ OneTimeSetup
          inc   $F1
          dex
          bne   -
+         ;X=0,Y=0
 
-         ldy   #0                    ; save a copy of ProDOS system global page
--        lda   $BF00, y              ; (will be copied back and forth by SwapProDOS later)
-         sta   $0F00, y
+-        lda   $BF00, y              ; save a copy of ProDOS system global page
+         sta   $0F00, y              ; (will be copied back and forth by SwapProDOS later)
          iny
          bne   -
+         ;X=0,Y=0
 
          lda   $FBB3                 ; ROM MachineID
          cmp   #$EA                  ; ][+?
@@ -55,7 +57,9 @@ OneTimeSetup
          lda   #$DF                  ; AND mask to force characters to uppercase on ][+
          sta   kForceLower
 +
-         jsr   ScanForDiskII         ; scan slots for Disk II drives
+         ;X=0,Y=0
+         +ScanForDiskII              ; scan slots for Disk II drives
+         ;X=0
          lda   DiskIIArray+5
          bne   +
          jsr   PrintByID             ; no Disk II in slot 6, this is fatal
@@ -63,6 +67,7 @@ OneTimeSetup
          jsr   WaitForKey
          jmp   CleanExit
 +
+         ;X=0
          jsr   ScanForRAMAndHardDisks; scan for things that look like RAM disks or hard disks
          +LoadPrefs                  ; load preferences (if available)
          jsr   ThisSlot              ; get information about selected drive and set gTargetType for main menu
@@ -80,7 +85,7 @@ OneTimeSetup
 
          jmp   MainMenu
 
-         !source "initscan.a"
+         !source "hw.harddisk.a"
 
 SHOW_PROGRESS_DURING_DECRUNCH = 1    ; activates optional UI code in exodecrunch