diff --git a/Source/HBIOS/hbios.asm b/Source/HBIOS/hbios.asm
index 2c15b811..d10cddfe 100644
--- a/Source/HBIOS/hbios.asm
+++ b/Source/HBIOS/hbios.asm
@@ -64,10 +64,6 @@
 ;  - dsky.asm
 ;  - unlzsa2s.asm
 ;
-; TODO
-; - Add remaining service routine stubs for IM3 (NMI, etc.)
-; - Fix app boot under Z280
-;
 ; INCLUDE GENERIC STUFF
 ;
 #INCLUDE "std.asm"
@@ -962,6 +958,23 @@ HB_IVT0F:	JP	HB_BADINT \ .DB 0
 ;==================================================================================================
 ;
 HB_START:
+#IFDEF APPBOOT
+  #IF (MEMMGR == MM_Z280)
+	LD	A,%00000001
+	OUT	(DIAGPORT),A
+	LD	DE,Z280_BOOTERR
+	LD	C,9
+	LD	A,%00000010
+	OUT	(DIAGPORT),A
+	CALL	$0005
+	LD	A,%00001000
+	OUT	(DIAGPORT),A
+	RET
+;
+Z280_BOOTERR	.TEXT	"\r\n\r\n*** Application mode boot not supported under Z280 native memory management!!!\r\n\r\n$"
+  #ENDIF
+#ENDIF
+
 	DI				; NO INTERRUPTS
 	IM	1			; INTERRUPT MODE 1
 ;
@@ -3602,16 +3615,109 @@ HB_BADINTCNT	.DB	0
 #IF (MEMMGR == MM_Z280)
 ;
 Z280_BADINT:
-	CALL	NEWLINE
+	; SAVE REASON CODE FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_RCSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+	; SAVE MSR FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_MSRSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+;
+	PUSH	DE
 	LD	DE,Z280_BADINTSTR
+	CALL	NEWLINE2
+	PRTS("+++ $")
 	CALL	WRITESTR
-	POP	HL			; DUMP MSR
-	POP	HL			; GET RET ADR
-	CALL	PRTHEXWORDHL
+	POP	DE
+	CALL	XREGDMP
+;
+	; RECOVER MSR, THEN RETURN VIA RETIL
+	PUSH	HL			; SAVE HL
+	LD	HL,(HB_RCSAV)		; GET SAVED REASON CODE
+	PRTS(" RC=$")
+	CALL	PRTHEXWORDHL		; DUMP MSR
+	LD	HL,(HB_MSRSAV)		; GET SAVED MSR
+	PRTS(" MSR=$")
+	CALL	PRTHEXWORDHL		; DUMP MSR
+	EX	(SP),HL			; MSR TO STK, RECOVER HL
+;
+	.DB	$ED,$55			; RETIL
+;
+Z280_SSTEP:
+	; SAVE HL AND MSR FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_MSRSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+;
+	PUSH	DE
+	LD	DE,Z280_SSTEPSTR
+	JP	Z280_DIAG
+;
+Z280_BRKHLT:
+	; SAVE HL AND MSR FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_MSRSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+;
+	PUSH	DE
+	LD	DE,Z280_BRKHLTSTR
+	JP	Z280_DIAG
+;
+Z280_DIVEXC:
+	; SAVE HL AND MSR FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_MSRSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+;
+	PUSH	DE
+	LD	DE,Z280_DIVEXCSTR
+	JP	Z280_DIAG
+;
+Z280_STKOVR:
+	; SAVE HL AND MSR FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_MSRSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+;
+	PUSH	DE
+	LD	DE,Z280_STKOVRSTR
+	JP	Z280_DIAG
+;
+Z280_ACCVIO:
+	; SAVE HL AND MSR FOR POSSIBLE RETURN VIA RETIL
+	EX	(SP),HL			; GET MSR, SAVE HL
+	LD	(HB_MSRSAV),HL		; SAVE IT
+	POP	HL			; RECOVER HL, POP STACK
+;
+	PUSH	DE
+	LD	DE,Z280_ACCVIOSTR
+	JP	Z280_DIAG
+;
+Z280_DIAG:
+	CALL	NEWLINE2
+	PRTS("+++ $")
+	CALL	WRITESTR
+	POP	DE
+	CALL	XREGDMP
+;
+	; RECOVER MSR, THEN RETURN VIA RETIL
+	PUSH	HL			; SAVE HL
+	LD	HL,(HB_MSRSAV)		; GET SAVED MSR
+	PRTS(" MSR=$")
+	CALL	PRTHEXWORDHL		; DUMP MSR
+	EX	(SP),HL			; MSR TO STK, RECOVER HL
+;
+	;.DB	$ED,$55			; RETIL
 	DI
 	HALT
 ;
-Z280_BADINTSTR	.TEXT	"\n\n*** Z280 BAD INT @$"
+Z280_BADINTSTR	.TEXT	"BAD INT $"
+Z280_SSTEPSTR	.TEXT	"SINGLE STEP $"
+Z280_BRKHLTSTR	.TEXT	"BREAK HALT $"
+Z280_DIVEXCSTR	.TEXT	"DIVISION EXCEPTION $"
+Z280_STKOVRSTR	.TEXT	"STACK OVERFLOW $"
+Z280_ACCVIOSTR	.TEXT	"ACCESS VIOLATION $"
 ;
 #ENDIF
 ;
@@ -3685,7 +3791,8 @@ Z280_PRIVINSTX:
 	EX	(SP),HL			; MSR TO STK, RECOVER HL
 	.DB	$ED,$55			; RETIL
 ;
-HB_MSRSAV	.DW	0
+HB_MSRSAV	.DW	0		; SAVED MSR
+HB_RCSAV	.DW	0		; SAVED REASON CODE
 ;
 Z280_PRIVSTR	.TEXT	"\r\n\r\n*** Privileged Instruction @$"
 ;
@@ -3898,27 +4005,27 @@ Z280_IVT:
 	.DW	$0000			; UART TRANSMITTER MSR
 	.DW	Z280_BADINT		; UART TRANSMITTER VECTOR
 	.DW	$0000			; SINGLE STEP TRAP MSR
-	.DW	Z280_BADINT		; SINGLE STEP TRAP VECTOR
+	.DW	Z280_SSTEP		; SINGLE STEP TRAP VECTOR
 	.DW	$0000			; BREAK ON HALT TRAP MSR
-	.DW	Z280_BADINT		; BREAK ON HALT TRAP VECTOR
+	.DW	Z280_BRKHLT		; BREAK ON HALT TRAP VECTOR
 	.DW	$0000			; DIVISION EXCEPTION TRAP MSR
-	.DW	Z280_BADINT		; DIVISION EXCEPTION TRAP VECTOR
+	.DW	Z280_DIVEXC		; DIVISION EXCEPTION TRAP VECTOR
 	.DW	$0000			; STACK OVERFLOW WARNING TRAP MSR
-	.DW	Z280_BADINT		; STACK OVERFLOW WARNING TRAP VECTOR
+	.DW	Z280_STKOVR		; STACK OVERFLOW WARNING TRAP VECTOR
 	.DW	$0000			; ACCESS VIOLATION TRAP MSR
-	.DW	Z280_BADINT		; ACCESS VIOLATION TRAP VECTOR
+	.DW	Z280_ACCVIO		; ACCESS VIOLATION TRAP VECTOR
 	.DW	$0000			; SYSTEM CALL TRAP MSR
 	.DW	Z280_SYSCALL		; SYSTEM CALL TRAP VECTOR
 	.DW	$0000			; PRIVILEGED INSTRUCTION TRAP MSR
 	.DW	Z280_PRIVINST		; PRIVILEGED INSTRUCTION TRAP VECTOR
 	.DW	$0000			; EPU <- MEMORY EXTENDED INSTRUCTION TRAP MSR
-	.DW	Z280_BADINT		; EPU <- MEMORY EXTENDED INSTRUCTION TRAP VECTOR
+	.DW	$0000			; EPU <- MEMORY EXTENDED INSTRUCTION TRAP VECTOR
 	.DW	$0000			; MEMORY <- EPU EXTENDED INSTRUCTION TRAP MSR
-	.DW	Z280_BADINT		; MEMORY <- EPU EXTENDED INSTRUCTION TRAP VECTOR
+	.DW	$0000			; MEMORY <- EPU EXTENDED INSTRUCTION TRAP VECTOR
 	.DW	$0000			; A <- EPU EXTENDED INSTRUCTION TRAP MSR
-	.DW	Z280_BADINT		; A <- EPU EXTENDED INSTRUCTION TRAP VECTOR
+	.DW	$0000			; A <- EPU EXTENDED INSTRUCTION TRAP VECTOR
 	.DW	$0000			; EPU INTERNAL OPERATION EXTENDED INSTRUCTION TRAP MSR
-	.DW	Z280_BADINT		; EPU INTERNAL OPERATION EXTENDED INSTRUCTION TRAP VECTOR
+	.DW	$0000			; EPU INTERNAL OPERATION EXTENDED INSTRUCTION TRAP VECTOR
 	.DW	0, 0			; RESERVED
 	.DW	0, 0			; RESERVED
 	; PROGRAM COUNTER VALUES FOR NMI/INTA
diff --git a/Source/HBIOS/usrrom.asm b/Source/HBIOS/usrrom.asm
index c230e0f9..ead329be 100644
--- a/Source/HBIOS/usrrom.asm
+++ b/Source/HBIOS/usrrom.asm
@@ -8,14 +8,11 @@ LF	.EQU    0AH
 ;
 	.ORG    USR_LOC
 ;           
-	LD	HL,BOOTMSG	; INTRODUCTION
+	LD	HL,BOOTMSG		; INTRODUCTION
 	CALL	PRTSTR
 
-	CALL	CIN		; DO STUFF
+	CALL	CIN			; DO STUFF
 ;
-	;LD      A,00H		; RETURN TO ROM LOADER
-	;LD      HL,0000H
-        ;JP	0FFF9H
 	LD	B,BF_SYSRESET		; SYSTEM RESTART
 	LD	C,BF_SYSRES_WARM	; WARM START
 	CALL	$FFF0			; CALL HBIOS
diff --git a/Source/HBIOS/util.asm b/Source/HBIOS/util.asm
index bccb3925..707c7ddf 100644
--- a/Source/HBIOS/util.asm
+++ b/Source/HBIOS/util.asm
@@ -125,7 +125,7 @@ PRTSTR:
 ; PRINT A STRING DIRECT: REFERENCED BY POINTER AT TOP OF STACK
 ; STRING MUST BE TERMINATED BY '$'
 ; USAGE:
-;   CALL PRTSTR
+;   CALL PRTSTRD
 ;   .DB  "HELLO$"
 ;   ...
 ;
diff --git a/Source/ver.inc b/Source/ver.inc
index 708cbf23..49dabc01 100644
--- a/Source/ver.inc
+++ b/Source/ver.inc
@@ -2,4 +2,4 @@
 #DEFINE	RMN	1
 #DEFINE	RUP	1
 #DEFINE	RTP	0
-#DEFINE BIOSVER	"3.1.1-pre.36"
+#DEFINE BIOSVER	"3.1.1-pre.38"
diff --git a/Source/ver.lib b/Source/ver.lib
index a71f2b66..973c277f 100644
--- a/Source/ver.lib
+++ b/Source/ver.lib
@@ -3,5 +3,5 @@ rmn	equ	1
 rup	equ	1
 rtp	equ	0
 biosver	macro
-	db	"3.1.1-pre.36"
+	db	"3.1.1-pre.38"
 	endm