diff --git a/defines_apple.s b/defines_apple.s
index fe39fc0..0591562 100644
--- a/defines_apple.s
+++ b/defines_apple.s
@@ -17,9 +17,8 @@ ZP_START2 = $55
 ;extra ZP variables
 USR				:= $000A
 
-
+; inputbuffer
 INPUTBUFFER     := $0200
-
 CONFIG_NO_INPUTBUFFER_ZP := 1
 CONFIG_INPUTBUFFER_0200 := 1
 
diff --git a/defines_cbm.s b/defines_cbm.s
index 8530a51..4c537a2 100644
--- a/defines_cbm.s
+++ b/defines_cbm.s
@@ -34,11 +34,9 @@ ZP_START0A = $04
 ZP_START1 = $5A
 ZP_START2 = $65
 
-;extra ZP variables
+; extra ZP variables
 Z03				:= $0003
 Z96				:= $020C
-
-; overlay ZP variables
 USR				:= GORESTART
 
 .else
@@ -49,19 +47,15 @@ ZP_START0A = $0E
 ZP_START1 = $03
 ZP_START2 = $13
 
-;extra ZP variables
+; extra/override ZP variables
 Z03				:= $000E
 Z96				:= $0096
-
-; overlay ZP variables
+POSX			:= $00C6
 TXPSV			:= LASTOP
 USR				:= GORESTART ; XXX
 
-; override ZP variables
-POSX			:= $00C6
-
+; inputbuffer
 INPUTBUFFER     := $0200
-
 CONFIG_NO_INPUTBUFFER_ZP := 1
 CONFIG_INPUTBUFFER_0200 := 1
 
@@ -81,6 +75,12 @@ CRLF_2 := LF
 
 RAMSTART2		:= $0400
 
+; magic memory locations
+.ifdef CBM1
+ENTROPY = $9044
+.else
+ENTROPY = $E844
+.endif
 
 ; monitor functions
 OPEN	:= $FFC0
@@ -100,11 +100,3 @@ CLALL	:= $FFE7
 LE7F3	:= $E7F3; for CBM1
 MONCOUT	:= CHROUT
 MONRDKEY := GETIN
-
-
-.ifdef CBM1
-ENTROPY = $9044
-.else
-ENTROPY = $E844
-.endif
-
diff --git a/defines_kbd.s b/defines_kbd.s
index cbb478f..325361a 100644
--- a/defines_kbd.s
+++ b/defines_kbd.s
@@ -18,30 +18,28 @@ ZP_START0A = $0F
 ZP_START1 = $06
 ZP_START2 = $15
 
-;extra ZP variables
+; extra/override ZP variables
 TXPSV           := $0049
 JMPADRS         := $0093
 LOWTRX          := $0094                        ; $AB also EXPSGN?
 Z96				:= $0096
-
-; override ZP variables
 Z17             := $06FC
 Z18             := $06FD
 
+; inputbuffer
 INPUTBUFFER     := $0700
-
 CONFIG_NO_INPUTBUFFER_ZP := 1
 
-; magic memory locations
-L06FE			:= $06FE
-L6874			:= $6874
-
 ; constants
 STACK_TOP		:= $FE
 SPACE_FOR_GOSUB := $49
 CRLF_1 := LF
 CRLF_2 := CR
 
+; magic memory locations
+L06FE			:= $06FE
+L6874			:= $6874
+
 ; memory layout
 RAMSTART2		:= $0300
 CONST_MEMSIZ	:= $3FFF
diff --git a/defines_kim.s b/defines_kim.s
index 2a60d3d..3db05a5 100644
--- a/defines_kim.s
+++ b/defines_kim.s
@@ -15,6 +15,13 @@ ZP_START0A = $15
 ZP_START1 = $0A
 ZP_START2 = $63
 
+; constants
+STACK_TOP		:= $FC
+SPACE_FOR_GOSUB := $36
+NULL_MAX		:= $F2 ; probably different in original version; the image I have seems to be modified; see PDF
+CRLF_1 := CR
+CRLF_2 := LF
+
 ; magic memory locations
 L1800           := $1800
 L1873           := $1873
@@ -23,10 +30,3 @@ L1873           := $1873
 MONRDKEY        := $1E5A
 MONCOUT         := $1EA0
 
-; constants
-STACK_TOP		:= $FC
-SPACE_FOR_GOSUB := $36
-NULL_MAX		:= $F2 ; probably different in original version; the image I have seems to be modified; see PDF
-CRLF_1 := CR
-CRLF_2 := LF
-
diff --git a/zeropage.s b/zeropage.s
index cfca350..6e7effb 100644
--- a/zeropage.s
+++ b/zeropage.s
@@ -3,15 +3,6 @@
 INPUTBUFFERX = INPUTBUFFER & $FF00
 
 ; overlay ZP variables, can be overridden
-.ifndef JMPADRS
-JMPADRS			:= DSCLEN + 1
-.endif
-.ifndef LOWTRX
-LOWTRX			:= LOWTR
-.endif
-.ifndef TXPSV
-TXPSV           := LINNUM
-.endif
 
 
 .feature org_per_seg
@@ -31,21 +22,24 @@ GOGIVEAYF:
 .org ZP_START0A
 Z15:
 	.res 1
-.ifndef POSX
+.ifndef POSX; allow override
 POSX:
 	.res 1
 .endif
-.ifndef Z17
+.ifndef Z17; allow override
 Z17:
 .endif
 	.res 1
-.ifndef Z18
+.ifndef Z18; allow override
 Z18:
 .endif
 	.res 1
 LINNUM:
+.ifndef TXPSV; allow override
+TXPSV:
+.endif
 	.res 2
-.ifndef INPUTBUFFER
+.ifndef INPUTBUFFER; allow override
 INPUTBUFFER:
 .endif
 
@@ -140,6 +134,9 @@ DSCPTR:
 .endif
 DSCLEN:
 	.res 2
+.ifndef JMPADRS ; allow override
+JMPADRS			:= DSCLEN + 1
+.endif
 Z52:
 	.res 1
 ARGEXTENSION:
@@ -165,6 +162,9 @@ TEMP2:
 EXPON:
 	.res 1
 LOWTR:
+.ifndef LOWTRX ; allow override
+LOWTRX:
+.endif
 	.res 1
 EXPSGN:
 	.res 1