diff --git a/src/4cade.init.machine.a b/src/4cade.init.machine.a
index d45ab0fb6..b95f9c920 100644
--- a/src/4cade.init.machine.a
+++ b/src/4cade.init.machine.a
@@ -13,3 +13,4 @@
          sta   STOREOFF
          sta   READMAINMEM
          sta   WRITEMAINMEM
+         sta   SETSTDZP
diff --git a/src/constants.a b/src/constants.a
index 6eb53a6da..a1435c3b4 100644
--- a/src/constants.a
+++ b/src/constants.a
@@ -77,16 +77,19 @@
 ; soft switches
 KBD =          $C000      ; last key pressed (if any)
 CLEARKBD =     $C010      ; clear last key pressed
-STOREOFF =     $C000      ; STA then use the following 4 flags:
-READMAINMEM =  $C002      ; STA to read from main mem
-READAUXMEM =   $C003      ; STA to read from aux mem
-WRITEMAINMEM = $C004      ; STA to write to main mem
-WRITEAUXMEM =  $C005      ; STA to write to aux mem
+
+STOREOFF =     $C000      ; STA then use the following flags:
+READMAINMEM =  $C002      ; STA to read from main mem ($0200..$BFFF)
+READAUXMEM =   $C003      ; STA to read from aux mem ($0200..$BFFF)
+WRITEMAINMEM = $C004      ; STA to write to main mem ($0200..$BFFF)
+WRITEAUXMEM =  $C005      ; STA to write to aux mem ($0200..$BFFF)
+
+SETSTDZP =     $C008      ; STA to r/w from main mem stack and zero page ($0000..$01FF)
 CLRC3ROM =     $C00A      ; STA to use internal Slot 3 ROM (required to use 128K and DHGR)
 SETC3ROM =     $C00B      ; STA to use external Slot 3 ROM (required to detect VidHD in slot 3)
-CLR80VID =     $C00C      ; 40 columns (also used to get out of DHGR mode)
-SET80VID =     $C00D      ; 80 columns (also used to get into DHGR mode)
-PRIMARYCHARSET= $C00E     ; no mousetext for you
+CLR80VID =     $C00C      ; STA to use 40 columns (also used to get out of DHGR mode)
+SET80VID =     $C00D      ; STA to use 80 columns (also used to get into DHGR mode)
+PRIMARYCHARSET= $C00E     ; STA to use no-mousetext character set
 SLOT3STATUS =  $C017      ; bit 7 only
 MONOCOLOR =    $C021      ; IIgs bit 7 switches composite mono/color modes
 TBCOLOR =      $C022      ; IIgs text foreground and background colors (also VidHD but write-only)
@@ -162,7 +165,7 @@ gVal         = $1F81      ; ""
 UILine1      = $1FB0      ; used by DrawUI
 UILine2      = $1FD8      ; ""
 UI_ToPlay    = $1FF7      ; ""
-ProBootEntry = $2025      ; used by ProBoot
+ProBootEntry = $2028      ; used by ProBoot
 gSearchIndex = $6000
 gSearchCache = $A000
 gPathname    = $BFD0      ; used by SetPath/AddToPath