diff --git a/auxmem.init.s b/auxmem.init.s
index ddce13d..3f0efcd 100644
--- a/auxmem.init.s
+++ b/auxmem.init.s
@@ -7,18 +7,18 @@
 * BBC Micro 'virtual machine' in Apple //e aux memory
 ***********************************************************
 
-MAXROM      EQU   $F9                        ; Max sideways ROM number
+MAXROM      EQU   $F9             ; Max sideways ROM number
 
-ZP1         EQU   $90                        ; $90-$9f are spare Econet space
-                                             ; so safe to use
+ZP1         EQU   $90             ; $90-$9f are spare Econet space
+                                  ; so safe to use
 ZP2         EQU   $92
 ZP3         EQU   $94
 
-STRTBCKL    EQU   $9D                        ; *TO DO* don't need to preserve
+STRTBCKL    EQU   $9D             ; *TO DO* No longer needed to preserve
 STRTBCKH    EQU   $9E
 
 MOSSHIM
-            ORG   AUXMOS                     ; MOS shim implementation
+            ORG   AUXMOS          ; MOS shim implementation
 
 *
 * Shim code to service Acorn MOS entry points using
@@ -28,8 +28,8 @@ MOSSHIM
 *
 * Initially executing at $3000 until copied to $D000
 
-MOSINIT     SEI                              ; Disable IRQ while initializing
-            LDX   #$FF                       ; Initialize Alt SP to $1FF
+MOSINIT     SEI                   ; Ensure IRQs disabled
+            LDX   #$FF            ; Initialize Alt SP to $1FF
             TXS
 
             STA   WRCARDRAM                  ; Make sure we are writing aux
@@ -105,11 +105,11 @@ MOSINIT     SEI                              ; Disable IRQ while initializing
 
 :NORELOC
 :S8         STA   SET80VID                   ; 80 col on
-            STA   CLRALTCHAR                 ; Alt charset off (?)
+            STA   CLRALTCHAR                 ; Alt charset off
             STA   PAGE2                      ; PAGE2
             JMP   MOSHIGH                    ; Ensure executing in high memory here
 
-MOSHIGH     SEI                              ; Disable IRQ while initializing
+MOSHIGH     SEI                              ; Ensure IRQs disabled
             LDX   #$FF
             TXS                              ; Initialise stack
             INX                              ; X=$00
@@ -137,70 +137,70 @@ MOSHIGH     SEI                              ; Disable IRQ while initializing
             LDA   #7
             JSR   OSWRCH
             JSR   OSNEWL
-            LDX   MAXROM                     ; TEMP X=language to enter
+            LDX   MAXROM          ; *TEMP* X=language to enter
             CLC
 
 * OSBYTE $8E - Enter language ROM
+*********************************
 * X=ROM number to select
 *
-BYTE8E      PHP                              ; Save CLC=RESET, SEC=Not RESET
-            JSR   ROMSELECT                  ; Bring ROM X into memory 
-            STX   BYTEVARBASE+$FC            ; Set current language ROM
+BYTE8E      PHP                   ; Save CLC=RESET, SEC=Not RESET
+            JSR   ROMSELECT       ; Bring ROM X into memory 
+            STX   BYTEVARBASE+$FC ; Set current language ROM
             LDA   #$00
             STA   FAULT+0
             LDA   #$80
             STA   FAULT+1
             LDY   #$09
-            JSR   PRERRLP                    ; Print ROM name with PRERR to set
-            STY   FAULT+0                    ;  FAULT pointing to version string
+            JSR   PRERRLP         ; Print ROM name with PRERR to set
+            STY   FAULT+0         ;  FAULT pointing to version string
             JSR   OSNEWL
             JSR   OSNEWL
-            PLP                              ; Get entry type back
-            LDA   #$01
+            PLP                   ; Get entry type back
+            LDA   #$01            ; $01=Entering code with a header
             JMP   ROMAUXADDR
 
+
 * OSBYTE $8F - Issue service call
+*********************************
 * X=service call, Y=parameter
 *
-SERVICE     TAX                              ; Enter here with A=Service Num
+SERVICE     TAX                   ; Enter here with A=Service Num
 BYTE8F
 SERVICEX    LDA   $F4
-            PHA                              ; Save current ROM
-
-*            LDA   $E0             ; *DEBUG*
-*            AND   #$20
-*            BEQ   :SERVDEBUG
-*            TXA
-*            JSR   PRHEX
-*            LDA   OSLPTR+1
-*            JSR   PRHEX
-*            LDA   OSLPTR+0
-*            JSR   PRHEX           ; *DEBUG*
-*:SERVDEBUG
+            PHA                   ; Save current ROM
 
+*DEBUG
+            LDA   $E0
+            AND   #$20            ; Test debug *OPT255,32
+            BEQ   :SERVDEBUG
+            CPX   #$06
+            BEQ   :SERVDONE       ; If debug on, ignore SERV06
+:SERVDEBUG
+*DEBUG
             TXA
-            LDX   MAXROM                     ; Start at highest ROM
-:SERVLP     JSR   ROMSELECT                  ; Bring it into memory
+            LDX   MAXROM          ; Start at highest ROM
+:SERVLP     JSR   ROMSELECT       ; Bring it into memory
             BIT   $8006
-            BPL   :SERVSKIP                  ; No service entry
-            JSR   $8003                      ; Call service entry
+            BPL   :SERVSKIP       ; No service entry
+            JSR   $8003           ; Call service entry
             TAX
             BEQ   :SERVDONE
-:SERVSKIP   LDX   $F4                        ; Restore X=current ROM
-            DEX                              ; Step down to next
-            BPL   :SERVLP                    ; Loop until ROM 0 done
-:SERVDONE   PLA                              ; Get caller's ROM back
-            PHX                              ; Save return from service call
+:SERVSKIP   LDX   $F4             ; Restore X=current ROM
+            DEX                   ; Step down to next
+            BPL   :SERVLP         ; Loop until ROM 0 done
+:SERVDONE   PLA                   ; Get caller's ROM back
+            PHX                   ; Save return from service call
             TAX
-            JSR   ROMSELECT                  ; Restore caller's ROM
-            PLX                              ; Get return value back
-            TXA                              ; Return in A and X and set EQ/NE
+            JSR   ROMSELECT       ; Restore caller's ROM
+            PLX                   ; Get return value back
+            TXA                   ; Return in A and X and set EQ/NE
             RTS
 
 
-PRHELLO     LDA   #<HELLO
+PRHELLO     LDX   #<HELLO
             LDY   #>HELLO
-            JSR   PRSTR
+            JSR   OSPRSTR
             JMP   OSNEWL
 
 BYTE00XX
@@ -211,12 +211,6 @@ BYTE00A     BRK
             DB    $F7
 HELLO       ASC   'Applecorn MOS 2022-10-15'
             DB    $00                        ; Unify MOS messages
+* TO DO: Move into RAM
 GSSPEED     DB    $00                        ; $80 if GS is fast, $00 for slow
 
-
-
-
-
-
-
-
diff --git a/auxmem.misc.s b/auxmem.misc.s
index b9bbce7..8f56a14 100644
--- a/auxmem.misc.s
+++ b/auxmem.misc.s
@@ -9,7 +9,7 @@
 * 26-Oct-2021 Corrected entry parameters to OSRDRM.
 * 03-Nov-2021 Temp'y fix, if can't find SROM, ignores it.
 * 13-Nov-2021 ROMSELECT calls mainmem to load ROM.
-* 08-Oct-2022 ROMSEL doesn't call loder if already paged in.
+* 08-Oct-2022 ROMSEL doesn't call loader if already paged in.
 
 
 * OSBYTE $80 - ADVAL
@@ -35,18 +35,14 @@ ADVALBUF    INX
             BEQ   :ADVALOK         ; Serial input, return 0
             LDX   #$01             ; For outputs, return 1 char free
             RTS
-:ADVALKBD   BIT   KEYBOARD         ; Test keyboard data/strobe
+:ADVALKBD   BIT   KBDDATA          ; Test keyboard data/strobe
             BPL   :ADVALOK         ; No Strobe, return 0
             INX                    ; Strobe, return 1
 :ADVALOK    RTS
 
 
-******************
-* Helper functions
-******************
-
 * Beep
-*
+******
 * Sound measurement shows the tone formula is:
 *   1.230 MHz
 * ------------- = cycles
@@ -61,7 +57,7 @@ ADVALBUF    INX
 *         (------------- - 10 ) / 5
 *         (8 * frequency      )
 
-* BEEPX     EQU   #57        ; note=C5
+* BEEPX     EQU   #57              ; note=C5
 BEEPX       EQU   #116             ; note=C4
 BEEP        PHA
             PHX
@@ -79,23 +75,26 @@ BEEP        PHA
             PLY                    ;
             PLX
             PLA
-            RTS
+PRSTROK     RTS
 
 
-* Print string pointed to by X,Y to the screen
+* OSPRSTR - Print string at XY
+******************************
+* On exit, X,Y preserved, A=$00
 OUTSTR      TXA
 
 * Print string pointed to by A,Y to the screen
 PRSTR       STA   OSTEXT+0         ;  String in A,Y
             STY   OSTEXT+1
 :L1         LDA   (OSTEXT)         ; Ptr to string in OSTEXT
-            BEQ   PRSTROK
-            JSR   OSASCI
+            PHP                    ; Save EQ
             INC   OSTEXT
-            BNE   :L1
+            BNE   :L2
             INC   OSTEXT+1
+:L2         PLP                    ; Get EQ back
+            BEQ   PRSTROK          ; End of string
+            JSR   OSASCI
             BRA   :L1
-PRSTROK     RTS
 
 * Print NL if not already at column 0
 FORCENL     LDA   #$86
@@ -104,12 +103,14 @@ FORCENL     LDA   #$86
             BEQ   PRSTROK
             JMP   OSNEWL
 
-* Print XY in hex
+* OSPR2HEX - Print XY in hex
+****************************
 OUT2HEX     TYA
             JSR   OUTHEX
             TXA                    ; Continue into OUTHEX
 
-* Print hex byte in A
+* OSPR1HEX - Print hex byte in A
+********************************
 OUTHEX      PHA
             LSR
             LSR
@@ -130,19 +131,8 @@ PRNIB       CMP   #$0A
 :S1         ADC   #'0'             ; < $0A
             JMP   OSWRCH
 
-* TEMP ENTRY *
-* Print 16-bit value in XY in decimal
-OSNUM       EQU   OSTEXT+0
-OSPAD       EQU   OSTEXT+4
-*PRDECXY
-*PRDECPAD    STX   OSNUM+0
-*            STY   OSNUM+1
-*            STZ   OSNUM+2
-*            STZ   OSNUM+3
-*:PRDEC16    LDY   #$05       ; 5 digits
-*            LDX   #OSNUM     ; number stored in OSNUM
-
-* Print up to 32-bit decimal number
+* OSPRDEC - Print up to 32-bit decimal number
+*********************************************
 * See forum.6502.org/viewtopic.php?f=2&t=4894
 * and groups.google.com/g/comp.sys.apple2/c/_y27d_TxDHA
 *
@@ -318,27 +308,31 @@ GSREADOK    INY                    ; Step to next character
 * VC=not control character
 
 
-* Read a byte from sideways ROM
+* OSRDROM - Read a byte from sideways ROM
+*****************************************
 * On entry, Y=ROM to read from
+*           (ROMPTR)=>byte to read
 * On exit,  A=byte read, X=current ROM, Y=$00
 RDROM       LDA   ROMID
             PHA                    ; Save current ROM
             TYA
             TAX                    ; X=ROM to read from
             JSR   ROMSELECT        ; Page in the required ROM
-            LDY   #$00
+            LDY   #$00             ; NOTE BBC sets Y=0, Master preserves
             LDA   (ROMPTR),Y       ; Read the byte
             PLX
 
-* Select a sideways ROM
-* X=ROM to select
-* All registers must be preserved
+* ROMSELECT - Select a sideways ROM
+***********************************
+* On entry, X=ROM to select
+* On exit,  All registers must be preserved
+*
 ROMSELECT
 * Insert code here for faking sideways ROMs by loading or otherwise
 * fetching code to $8000. All registers must be preserved.
             PHP
             CPX   ROMID            ; Speed up by checking if
-*            BEQ   ROMSELOK         ; already paged in
+            BEQ   ROMSELOK         ; already paged in
 * BUG: This needs ROMID an invalid value on startup so first access works
             PHA
             PHX
@@ -354,11 +348,6 @@ ROMSELDONE  >>>   ENTAUX
 ROMSELOK    PLP
             RTS
 
-
-
-EVENT       RTS
-
-
 * Initialize ROMTAB according to user selection in menu
 ROMINIT     STZ   MAXROM           ; One sideways ROM only
             STA   RDMAINRAM        ; Read main mem
@@ -371,7 +360,12 @@ ROMINIT     STZ   MAXROM           ; One sideways ROM only
 :X1         CMP   #7
             BNE   :X2
             STA   MAXROM
-:X2         RTS
+:X2         LDA   #$FF
+            STA   ROMID            ; Ensure set to invalid value
+            RTS
+
+
+EVENT       RTS
 
 
 **********************************************************
@@ -384,6 +378,7 @@ GSBRKAUX    >>>   IENTAUX          ; IENTAUX does not do CLI
 * TO DO: Check, IENTAUX modifies X
 
 * IRQ/BRK handler
+*****************
 IRQBRKHDLR  PHA
 * Mustn't enable IRQs within the IRQ handler
 * Do not use WRTMAIN/WRTAUX macros
@@ -428,6 +423,20 @@ IRQBRKRET
             PLA
 NULLRTI     RTI
 
+* Default BRK handler
+*********************
+MOSBRKHDLR  LDX   #<MSGBRK
+            LDY   #>MSGBRK
+            JSR   OSPRSTR
+            JSR   PRERR
+*            JSR   OSNEWL
+*            JSR   OSNEWL
+STOP        JMP   STOP             ; Cannot return from a BRK
+
+MSGBRK      DB    $0D
+            ASC   'ERROR: '
+            DB    $00
+
 PRERR       LDY   #$01
 PRERRLP     LDA   (FAULT),Y
             BEQ   PRERR1
@@ -437,20 +446,9 @@ PRERRLP     LDA   (FAULT),Y
 NULLRTS
 PRERR1      RTS
 
-MOSBRKHDLR  LDA   #<MSGBRK
-            LDY   #>MSGBRK
-            JSR   PRSTR
-            JSR   PRERR
-            JSR   OSNEWL
-            JSR   OSNEWL
-STOP        JMP   STOP             ; Cannot return from a BRK
-
-MSGBRK      DB    $0D
-            ASC   'ERROR: '
-            DB    $00
-
 
 * Default page 2 contents
+*************************
 DEFVEC      DW    NULLRTS          ; $200 USERV
             DW    MOSBRKHDLR       ; $202 BRKV
             DW    NULLRTI          ; $204 IRQ1V
@@ -500,7 +498,8 @@ OSSCANDEC   JMP   SCANDEC          ; FF9E SCANDEC
 OSSCANHEX   JMP   SCANHEX          ; FFA1 SCANHEX
 OSFFA4      JMP   NULLRTS          ; FFA4 (DISKACC)
 OSFFA7      JMP   NULLRTS          ; FFA7 (DISKCCP)
-PRHEX       JMP   OUTHEX           ; FFAA PRHEX
+PRHEX
+PR1HEX      JMP   OUTHEX           ; FFAA PRHEX
 PR2HEX      JMP   OUT2HEX          ; FFAD PR2HEX
 OSFFB0      JMP   PRINTDEC         ; FFB0 (USERINT)
 OSWRRM      JMP   NULLRTS          ; FFB3 OSWRRM
@@ -544,8 +543,6 @@ MOSVEND
 
 * Buffer for one 512 byte disk block in aux mem
 AUXBLK
-;ASC   '**ENDOFCODE**'
-;            DS    $200-13
-
-
+;           ASC   '**ENDOFCODE**'
+;           DS    $200-13
 
diff --git a/auxmem.mosequ.s b/auxmem.mosequ.s
index ff6cb49..1f939d8 100644
--- a/auxmem.mosequ.s
+++ b/auxmem.mosequ.s
@@ -17,34 +17,36 @@
 * $EF-$FF MOS API workspace
 
 * DEBUG       EQU   $00         ; $00=*OPT 255 debug code removed
-DEBUG        EQU   $E0         ; $E0=*OPT 255 debug code included
-*                             ; $E1
-FSFLAG1      EQU   $E2         ; $E2
-FSFLAG2      EQU   $E3         ; $E3 HOSTFS *OPT settings
-GSFLAG       EQU   $E4         ; $E4 GSREAD processing flags
-GSCHAR       EQU   $E5         ; $E5 GSREAD accumulator
-OSTEXT       EQU   $E6         ; $E6 => text string  $E6 OSNUM+0
-MAXLEN       EQU   OSTEXT+2    ; $E8                 $E8 OSNUM+2
-MINCHAR      EQU   OSTEXT+3    ; $E9                 $E9 OSNUM+3
-MAXCHAR      EQU   OSTEXT+4    ; $EA                 $EA OSPAD
-OSTEMP       EQU   $EB         ; $EB                 $EB OSTEMP
-OSKBD1       EQU   $EC         ; $EC kbd ws
-OSKBD2       EQU   OSKBD1+1    ; $ED kbd ws
-OSKBD3       EQU   OSKBD1+2    ; $EE kbd ws
-OSAREG       EQU   $EF         ; $EF   A  register
-OSXREG       EQU   OSAREG+1    ; $F0   X  register
-OSYREG       EQU   OSXREG+1    ; $F1   Y  register
-OSCTRL       EQU   OSXREG      ; $F0  (XY)=>control block
-OSLPTR       EQU   $F2         ; $F2 => command line
-ROMID        EQU   $F4         ; $F4 current ROM 
-ROMTMP       EQU   $F5         ; $F5 
-ROMPTR       EQU   $F6         ; $F6 =>
-*                             ; $F8 *TEMP* pseudo-SROM settings
-*                             ; $F9 *TEMP* pseudo-SROM settings
-OSINTWS      EQU   $FA         ; $FA  IRQ ZP pointer, use when IRQs off
-OSINTA       EQU   $FC         ; $FC  IRQ register A store
-FAULT        EQU   $FD         ; $FD  Error message pointer
-ESCFLAG      EQU   $FF         ; $FF  Escape status
+DEBUG       EQU   $E0         ; $E0=*OPT 255 debug code included
+* GSSPEED     EQU   $E1         ; $E1 **TEMP**
+FSFLAG1     EQU   $E2         ; $E2
+FSFLAG2     EQU   $E3         ; $E3 HOSTFS *OPT settings
+GSFLAG      EQU   $E4         ; $E4 GSREAD processing flags
+GSCHAR      EQU   $E5         ; $E5 GSREAD accumulator
+OSTEXT      EQU   $E6         ; $E6 => text string  $E6 OSNUM+0
+MAXLEN      EQU   OSTEXT+2    ; $E8                 $E8 OSNUM+2
+MINCHAR     EQU   OSTEXT+3    ; $E9                 $E9 OSNUM+3
+MAXCHAR     EQU   OSTEXT+4    ; $EA                 $EA OSPAD
+OSNUM       EQU   OSTEXT      ; $E6
+OSPAD       EQU   OSNUM+4     ; $EA
+OSTEMP      EQU   $EB         ; $EB
+OSKBD1      EQU   $EC         ; $EC kbd ws
+OSKBD2      EQU   OSKBD1+1    ; $ED kbd ws
+OSKBD3      EQU   OSKBD1+2    ; $EE kbd ws
+OSAREG      EQU   $EF         ; $EF   A  register
+OSXREG      EQU   OSAREG+1    ; $F0   X  register
+OSYREG      EQU   OSXREG+1    ; $F1   Y  register
+OSCTRL      EQU   OSXREG      ; $F0  (XY)=>control block
+OSLPTR      EQU   $F2         ; $F2 => command line
+ROMID       EQU   $F4         ; $F4 current ROM 
+ROMTMP      EQU   $F5         ; $F5 
+ROMPTR      EQU   $F6         ; $F6 => ROM addresses
+*                             ; $F8 pseudo-SROM settings
+ROMMAX      EQU   $F9         ; $F9 pseudo-SROM settings: maximum ROM number
+OSINTWS     EQU   $FA         ; $FA IRQ ZP pointer, use when IRQs off
+OSINTA      EQU   $FC         ; $FC IRQ register A store
+FAULT       EQU   $FD         ; $FD Error message pointer
+ESCFLAG     EQU   $FF         ; $FF Escape status
 
 
 * $0200-$0235 Vectors
@@ -52,31 +54,25 @@ ESCFLAG      EQU   $FF         ; $FF  Escape status
 * $0290-$02ED
 * $02EE-$02FF MOS control block
 
-USERV        EQU   $200        ; USER vector
-BRKV         EQU   $202        ; BRK vector
-CLIV         EQU   $208        ; OSCLI vector
-BYTEV        EQU   $20A        ; OSBYTE vector
-WORDV        EQU   $20C        ; OSWORD vector
-WRCHV        EQU   $20E        ; OSWRCH vector
-RDCHV        EQU   $210        ; OSRDCH vector
-FILEV        EQU   $212        ; OSFILE vector
-ARGSV        EQU   $214        ; OSARGS vector
-BGETV        EQU   $216        ; OSBGET vector
-BPUTV        EQU   $218        ; OSBPUT vector
-GBPBV        EQU   $21A        ; OSGBPB vector
-FINDV        EQU   $21C        ; OSFIND vector
-FSCV         EQU   $21E        ; FSCV misc file ops
+USERV       EQU   $200        ; USER vector
+BRKV        EQU   $202        ; BRK vector
+CLIV        EQU   $208        ; OSCLI vector
+BYTEV       EQU   $20A        ; OSBYTE vector
+WORDV       EQU   $20C        ; OSWORD vector
+WRCHV       EQU   $20E        ; OSWRCH vector
+RDCHV       EQU   $210        ; OSRDCH vector
+FILEV       EQU   $212        ; OSFILE vector
+ARGSV       EQU   $214        ; OSARGS vector
+BGETV       EQU   $216        ; OSBGET vector
+BPUTV       EQU   $218        ; OSBPUT vector
+GBPBV       EQU   $21A        ; OSGBPB vector
+FINDV       EQU   $21C        ; OSFIND vector
+FSCV        EQU   $21E        ; FSCV misc file ops
 
-BYTEVARBASE  EQU   $190        ; Base of OSBYTE variables
-OSFILECB     EQU   $2EE        ; OSFILE control block
-OSGBPBCB     EQU   OSFILECB+1  ; OSGBPB control block
+BYTEVARBASE EQU   $190        ; Base of OSBYTE variables
+OSFILECB    EQU   $2EE        ; OSFILE control block
+OSGBPBCB    EQU   OSFILECB+1  ; OSGBPB control block
 
 
 * $0300-$03DF
 * $03E0-$03FF Used for interfacing with ProDOS XFER
-
-
-
-
-
-
diff --git a/mainmem.audio.s b/mainmem.audio.s
index 3a90441..5e5b674 100644
--- a/mainmem.audio.s
+++ b/mainmem.audio.s
@@ -176,9 +176,10 @@ MAININS     >>>   ENTMAIN
 
 
 * Remove value from buffer or examine buffer (API same as Acorn MOS REMV)
+* NOTE OS1.20 has a bug in the EXAMINE path
 * On entry: X is buffer number, V=1 if only examination is requested
-* On exit: If examination, A next byte, X preserved, Y=offset to next char
-*          If removal, A undef, X preserved, Y value of byte removed
+* On exit: If examination, A next byte, X preserved, Y=next byte
+*          If removal, A undef, X preserved, Y=value of byte removed
 *          If buffer already empty C=1, else C=0
 REM         PHP                              ; Save flags, turn off interrupts
             SEI
@@ -201,6 +202,7 @@ REM         PHP                              ; Save flags, turn off interrupts
             CLC                              ; Success
             RTS
 :EXAM       PLA                              ; Char read from buffer
+            TAY                              ; BUGFIX: Omitted on OS1.20
             PLP
             CLC                              ; Success
             RTS