diff --git a/Source/HBIOS/hbios.asm b/Source/HBIOS/hbios.asm
index e696311f..bd9bf181 100644
--- a/Source/HBIOS/hbios.asm
+++ b/Source/HBIOS/hbios.asm
@@ -115,12 +115,23 @@ MODCNT	.SET	MODCNT + 1
 ; NO INTERRUPT HANDLING
 #DEFINE	HB_DI		;
 #DEFINE	HB_EI		;
-#ENDIF
-#IF ((INTMODE == 1) | (INTMODE == 2) | (INTMODE == 3))
-; MODE 1 OR 2 OR 3 INTERRUPT HANDLING
+#ELSE
+  #IF (CPUFAM == CPU_Z280)
+    #IF (INTMODE == 3)
+; Z280 MODE 3 INTERRUPT HANDLING (INTA & UART ENABLED)
+#DEFINE	HB_DI		DI
+#DEFINE	HB_EI		.DB	$ED,$F7,$09
+    #ELSE
+; Z280 MODE 1/2 INTERRUPT HANDLING
 #DEFINE	HB_DI		DI
 #DEFINE	HB_EI		EI
+    #ENDIF
+  #ELSE
+#DEFINE	HB_DI		DI
+#DEFINE	HB_EI		EI
+  #ENDIF
 #ENDIF
+;
 #IF (INTMODE > 3)
 	.ECHO	"*** ERROR: INVALID INTMODE SETTING!!!\n"
 	!!!	; FORCE AN ASSEMBLY ERROR
@@ -300,10 +311,7 @@ HBX_IDENT:
 ; ACCOMMODATE FREERTOS.  HBX_BUF IS ONLY USED AS A BOUNCE BUFFER, SO IT'S
 ; USE WILL NEVER OVERLAP WITH BELOW.
 ;
-; HBX_INVOKE IS NOT RE-ENTRANT!  HB_INVBNK CAN BE USED GLOBALLY TO DETERMINE
-; IF HBIOS IS ALREADY ACTIVE.  HB_INVBNK WILL HAVE A VALUE != $FF WHEN HBIOS
-; IS ACTIVE.  ON RETURN, HB_INVBNK IS SET TO $FF TO INDICATE HBIOS IS NOT
-; ACTIVE.
+; WARNING: HBX_INVOKE IS *NOT* REENTRANT!
 ;
 HBX_INVOKE:
 
@@ -500,10 +508,10 @@ HBX_BNKCPY:
 	.DB	$ED,$66			; LDCTL HL,(C)
 	POP	BC
 	EX	(SP),HL
-	DI
+	HB_DI
   #ELSE
 	LD	A,I
-	DI
+	HB_DI
 	PUSH	AF
   #ENDIF
 	LD	(HBX_BC_SP),SP		; PUT STACK
@@ -545,7 +553,7 @@ HBX_BC_SP	.EQU	$ - 2		; ... TO ORIGINAL VALUE
   #ELSE
 	POP	AF
 	JP	PO,$+4
-	EI
+	HB_EI
   #ENDIF
 	RET
 ;
@@ -576,6 +584,48 @@ HBX_BC_ITER:
 ; ON INPUT A=TARGET BANK, IX=TARGET ADDRESS
 ;
 HBX_BNKCALL:
+;
+#IF (MEMMGR == MM_Z280)
+	JR	HBX_BNKCALL2
+
+	CP	BID_BIOS		; CALLING HBIOS?
+	JR	NZ,HBX_BNKCALL2		; NOPE, DO NORMAL PROCESSING
+	
+	;PUSH	AF
+	;LD	A,'['
+	;.DB	$ED,$71			; SC
+	;.DW	COUT			; SC PARAMETER
+	;POP	AF
+	
+	;
+	;LD	A,(HB_CURBNK)		; GET CURRENT BANK
+	;LD	(HB_INVBNK),A		; SAVE INVOCATION BANK
+	;
+	;LD	A,BID_BIOS		; HBIOS BANK
+	;LD	(HB_CURBNK),A		; SET AS CURRENT BANK
+
+	LD	(HBX_BNKCALL1+2),IX	; SETUP TARGET ADDRESS
+HBX_BNKCALL1:
+	.DB	$ED,$71			; SC
+	.DW	$FFFF			; SC PARAMETER (SET ABOVE)
+	
+	;PUSH	AF
+	;LD	A,']'
+	;.DB	$ED,$71			; SC
+	;.DW	COUT			; SC PARAMETER
+	;POP	AF
+	
+	;PUSH	AF
+	;LD	A,(HB_INVBNK)
+	;LD	(HB_CURBNK),A
+	;POP	AF
+	
+	
+	
+	RET
+#ENDIF
+
+HBX_BNKCALL2:
 	LD	(HBX_TGTBNK),A		; STUFF TARGET BANK TO CALL INTO CODE BELOW
 	LD	(HBX_TGTADR),IX		; STUFF ADDRESS TO CALL INTO CODE BELOW
 	LD	A,(HB_CURBNK)		; GET CURRENT BANK
@@ -956,7 +1006,7 @@ HB_START:
 	; INITIALIZE MMU
 	; START BY SELECTING I/O PAGE $FF
 	LD	L,$FF			; MMU AND DMA PAGE I/O REG IS $FF
-	LD	C,$08			; REG C POINTS TO I/O PAGE REGISTER
+	LD	C,Z280_IOPR		; REG C POINTS TO I/O PAGE REGISTER
 	.DB	$ED,$6E			; LDCTL	(C),HL
 ;
 	; INITIALIZE ALL OF THE SYSTEM PAGE DESCRIPTORS WITH BLOCK MOVE
@@ -979,13 +1029,18 @@ HB_START:
 	LD	C,Z280_MMUMCR		; MMU MASTER CONTROL REGISTER
 	LD	HL,$BBFF		; ENABLE USER & SYSTEM TRANSLATE
 	.DB	$ED,$BF			; OUTW (C),HL
-; 	
+;
+	; DISABLE MEMORY REFRESH CYCLES
+	LD	A,$08			; DISABLED
+	OUT	(Z280_RRR),A		; SET REFRESH RATE REGISTER
+	
 	; RESTORE I/O PAGE TO $00
 	LD	L,$00			; NORMAL I/O REG IS $00
-	LD	C,$08			; REG C POINTS TO I/O PAGE REGISTER
+	LD	C,Z280_IOPR		; REG C POINTS TO I/O PAGE REGISTER
 	.DB	$ED,$6E			; LDCTL	(C),HL
 ;
 	; CONFIGURE Z280 INT/TRAP VECTOR TABLE POINTER REGISTER
+	; WILL POINT TO ROM COPY FOR NOW, UPDATED TO RAM LATER ON
 	LD	C,Z280_VPR
 	LD	HL,Z280_IVT >> 8	; TOP 16 BITS OF PHYSICAL ADR OF IVT
 	.DB	$ED,$6E			; LDCTL	(C),HL
@@ -2037,6 +2092,9 @@ HB_PCINITTBL:
 #IF (ACIAENABLE)
 	.DW	ACIA_PREINIT
 #ENDIF
+#IF (Z2UENABLE)
+	.DW	Z2U_PREINIT
+#ENDIF
 #IF (PIO_4P | PIO_ZP)
 	.DW	PIO_PREINIT
 #ENDIF
@@ -2080,6 +2138,9 @@ HB_INITTBL:
 #IF (ACIAENABLE)
 	.DW	ACIA_INIT
 #ENDIF
+#IF (Z2UENABLE)
+	.DW	Z2U_INIT
+#ENDIF
 #IF (DSRTCENABLE)
 	.DW	DSRTC_INIT
 #ENDIF
@@ -2798,7 +2859,7 @@ SYS_VER:
 ; SET ACTIVE MEMORY BANK AND RETURN PREVIOUSLY ACTIVE MEMORY BANK
 ;   NOTE THAT IT GOES INTO EFFECT AS HBIOS FUNCTION IS EXITED
 ;   HERE, WE JUST SET THE CURRENT BANK
-;   CALLER MUST ESTABLISH UPPER MEMORY STACK BEFORE INVOKING THIS FUNCTION!
+;   CALLER MUST EXTABLISH UPPER MEMORY STACK BEFORE INVOKING THIS FUNCTION!
 ;
 SYS_SETBNK:
 #IF (MEMMGR == MM_Z280)
@@ -3189,10 +3250,10 @@ SYS_PEEK:
 	LD	C,Z280_MSR
 	.DB	$FD,$ED,$66		; LDCTL	IY,(C)
 	PUSH	IY
-	DI
+	HB_DI
   #ELSE
-	LD	A,I			; SAVE THE INTERRUPT STATUS
-	DI				;  COPY IFF2 TO P/V FLAG
+	LD	A,I
+	DI
 	PUSH	AF
   #ENDIF
 #ENDIF
@@ -3204,9 +3265,9 @@ SYS_PEEK:
 	.DB	$FD,$ED,$6E		; LDCTL	(C),IY
 	POP	IY
   #ELSE
-	POP	AF			; RECALL INITIAL INTERRUPT STATUS
-	JP	PO,$+4			; RETURN TO INITIAL STATE
-	EI
+	POP	AF
+	JP	PO,$+4
+	HB_EI
   #ENDIF
 #ENDIF
 	XOR	A
@@ -3226,10 +3287,10 @@ SYS_POKE:
 	LD	C,Z280_MSR
 	.DB	$FD,$ED,$66		; LDCTL	IY,(C)
 	PUSH	IY
-	DI
+	HB_DI
   #ELSE
 	LD	A,I
-	DI
+	HB_DI
 	PUSH	AF
   #ENDIF
 #ENDIF
@@ -3243,7 +3304,7 @@ SYS_POKE:
   #ELSE
 	POP	AF
 	JP	PO,$+4
-	EI
+	HB_EI
   #ENDIF
 #ENDIF
 	XOR	A
@@ -3495,63 +3556,65 @@ Z280_BADINTSTR	.TEXT	"\n\n*** Z280 BAD INT @$"
 #IF (MEMMGR == MM_Z280)
 ;
 Z280_PRIVINST:
+	; 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
 	EX	(SP),HL			; GET ADR, SAVE HL
-	
+;	
 	PUSH	AF
 	PUSH	BC
 	PUSH	DE
-	
+;	
 	.DB	$ED,$96			; LDUP	A,(HL)
-	INC	HL			; BUMP PAST PRIV INST
 	
 	;CALL	PC_LBKT
 	;CALL	PRTHEXBYTE
 	;CALL	PC_RBKT
-	
+;	
 	; HANDLE DI
 	CP	$F3			; DI?
 	JR	NZ,Z280_PRIVINST2
-	DI				; DO THE DI
+	HB_DI				; DO THE DI
+	INC	HL			; BUMP PAST IT
 	JR	Z280_PRIVINSTX
-
+;
 Z280_PRIVINST2:
 	; HANDLE EI
 	CP	$FB			; EI?
-	JR	NZ,Z280_PRIVINST_HALT
-	EI				; DO THE EI
+	JR	NZ,Z280_PRIVINST3
+	HB_EI				; DO THE EI
+	INC	HL			; BUMP PAST IT
 	JR	Z280_PRIVINSTX
-
-Z280_PRIVINST_HALT:
+;
+Z280_PRIVINST3:
 	; SOMETHING ELSE, DIAGNOSE & HALT SYSTEM
-	
-	PUSH	HL
+	LD	DE,Z280_PRIVSTR
+	CALL	WRITESTR
+	CALL	PRTHEXWORDHL
+;
+	; DUMP 16 BYTES OF USER ADDRESS SPACE
+	CALL	PC_SPACE
 	CALL	PC_LBKT
-	CALL	PRTHEXBYTE
+	LD	B,$10
+Z280_PRIVINST4:
 	.DB	$ED,$96			; LDUP	A,(HL)
 	CALL	PRTHEXBYTE
 	INC	HL
-	.DB	$ED,$96			; LDUP	A,(HL)
-	CALL	PRTHEXBYTE
+	DJNZ	Z280_PRIVINST4
 	CALL	PC_RBKT
-	POP	HL
-
-	CALL	NEWLINE
-	LD	DE,Z280_PRIVSTR
-	CALL	WRITESTR
-	DEC	HL
-	CALL	PRTHEXWORDHL
-	
+;
+	; GO NO FURTHER
 	DI
 	HALT
-
-Z280_PRIVINSTX:	
+;
+Z280_PRIVINSTX:
+	; RESTORE REGISTERS
 	POP	DE
 	POP	BC
 	POP	AF
-	
+;
+	; RECOVER HL AND MSR, THEN RETURN VIA RETIL
 	EX	(SP),HL			; RECOVER HL, ADR TO STK
 	PUSH	HL			; SAVE HL
 	LD	HL,(HB_MSRSAV)		; GET SAVED MSR
@@ -3560,7 +3623,7 @@ Z280_PRIVINSTX:
 ;
 HB_MSRSAV	.DW	0
 ;
-Z280_PRIVSTR	.TEXT	"\n\n*** Privileged Instruction @$"
+Z280_PRIVSTR	.TEXT	"\r\n\r\n*** Privileged Instruction @$"
 ;
 #ENDIF
 ;
@@ -3737,7 +3800,7 @@ HB_TMPREF	.DW	0
 ;   Z280 INTERRUPT VECTOR TABLE
 ;==================================================================================================
 ;
-#IF (MEMMGR = MM_Z280)
+#IF (MEMMGR == MM_Z280)
 ;
 	.FILL	$1000 - ($ & $FFF)	; MUST BE 4K ALIGNED!
 ;
@@ -3834,19 +3897,17 @@ Z280_BNKSEL:
 	LD	C,Z280_IOPR		; I/O PAGE REGISTER TO C
 	.DB	$ED,$6E			; LDCTL (C),HL
 ;
-	; POINT HL TO PORTION OF TABLE TO PROGRAM PDRS WITH
-	LD	HL,Z280_PDRTBL		; POINT TO PDR TABLE
-	SLA	A			; BANK ID TIMES TWO, RAM BIT TO C
-	JR	NC,Z280_BNKSEL1		; IF ROM, SKIP AHEAD
-	INC	H			; HANDLE RAM OFFSET
+	; POINT HL TO STARTING ENTRY TO PROGRAM
+	; OPTIMIZED TO ASSUME HL IS PAGE ALIGNED!
+	LD	H,Z280_PDRTBL >> 8
+	SLA	A
+	JR	NC,Z280_BNKSEL1
+	INC	H
 Z280_BNKSEL1:
 	RLCA
 	RLCA
 	RLCA
-	ADD	A,L
 	LD	L,A
-	JR	NC,Z280_BNKSEL2		; NO CARRY, SKIP AHEAD
-	INC	H			; HANDLE CARRY
 ;
 Z280_BNKSEL2:
 	; POINT TO FIRST PDR TO PROGRAM ($00=USER, $10=SYSTEM)
@@ -3867,6 +3928,11 @@ Z280_BNKSEL2:
 	POP	BC
 	RET
 ;
+#IF (($ & $FF) != 0)
+	; PAGE ALIGN THE TABLE
+	.FILL	$100 - ($ & $FF)
+#ENDIF
+;
 #IF (($ % 2) == 1)
 	; BYTE ALIGN THE TABLE
 	.DB	0
@@ -4172,7 +4238,7 @@ Z280_BNKSEL:
 	PUSH	DE
 	PUSH	BC
 	LD	L,$FF			; MMU PAGE I/O REG IS $FF
-	LD	C,8			; REG C POINTS TO I/O PAGE REGISTER
+	LD	C,Z280_IOPR		; REG C POINTS TO I/O PAGE REGISTER
 	.DB	$ED,$6E			; OP CODE FOR LDCTL (C),HL
 	LD	E,0			; DE IS TEMPLATE
 	BIT	7,A
@@ -4236,7 +4302,7 @@ W_MMU1:
 W_MMU2:        
 	;.DB    $ED,$65			; PCACHE
 	LD	L,0                     ; RESTORE I/O PAGE REG TO 0
-	LD	C,8
+	LD	C,Z280_IOPR
 	.DB	$ED,$6E			; LDCTL (C),HL
 	POP	BC
 	POP	DE
@@ -4453,6 +4519,15 @@ SIZ_ACIA	.EQU	$ - ORG_ACIA
 		.ECHO	" bytes.\n"
 #ENDIF
 ;
+#IF (Z2UENABLE)
+ORG_Z2U	.EQU	$
+  #INCLUDE "z2u.asm"
+SIZ_Z2U	.EQU	$ - ORG_Z2U
+		.ECHO	"Z2U occupies "
+		.ECHO	SIZ_Z2U
+		.ECHO	" bytes.\n"
+#ENDIF
+;
 #IF (VGAENABLE)
 ORG_VGA	.EQU	$
   #INCLUDE "vga.asm"
@@ -5483,8 +5558,8 @@ PS_FLP_DSTR:	.TEXT	"SD$"		; PS_FLPSD
 ; CHARACTER DEVICE STRINGS
 ;
 PS_SDSTRREF:
-	.DW	PS_SDUART, PS_SDASCI, PS_SDTERM
-	.DW	PS_SDPRPCON, PS_SDPPPCON, PS_SDSIO, PS_SDACIA, PS_SDPIO,PS_SDUF,PS_SDDUART
+	.DW	PS_SDUART, PS_SDASCI, PS_SDTERM, PS_SDPRPCON, PS_SDPPPCON
+	.DW	PS_SDSIO, PS_SDACIA, PS_SDPIO, PS_SDUF, PS_SDDUART, PS_SDZ2U
 ;
 PS_SDUART	.TEXT	"UART$"
 PS_SDASCI	.TEXT	"ASCI$"
@@ -5496,6 +5571,7 @@ PS_SDACIA	.TEXT	"ACIA$"
 PS_SDPIO	.TEXT	"PORT$"
 PS_SDUF		.TEXT	"UF$"
 PS_SDDUART	.TEXT	"DUART$"
+PS_SDZ2U	.TEXT	"Z2U$"
 ;
 ; CHARACTER SUB TYPE STRINGS
 ;