diff --git a/Source/HBIOS/asci.asm b/Source/HBIOS/asci.asm
index 5e3246bc..57ee1e16 100644
--- a/Source/HBIOS/asci.asm
+++ b/Source/HBIOS/asci.asm
@@ -87,7 +87,7 @@ ASCI1_IVT	.EQU	IVT(INT_SER1)
 ASCI_PREINIT:
 ;
 ; SETUP THE DISPATCH TABLE ENTRIES
-; NOTE: INTS WILL BE DISABLED WHEN PREINIT IS CALLED AND THEY MUST REMIAIN
+; NOTE: INTS WILL BE DISABLED WHEN PREINIT IS CALLED AND THEY MUST REMAIN
 ; DISABLED.
 ;
 	LD	B,ASCI_CFGCNT		; LOOP CONTROL
diff --git a/Source/HBIOS/updater.asm b/Source/HBIOS/updater.asm
index 60fc5811..1d0013f4 100644
--- a/Source/HBIOS/updater.asm
+++ b/Source/HBIOS/updater.asm
@@ -62,11 +62,13 @@
 ;  ONTO FLASH #2. THE PURPOSE OF THIS IS TO ENABLE MAKING A BACKUP COPY OF
 ;  THE CURRENT FLASH. 
 ;
+; OPTION (1) AND (2) - CALCULATE AND DISPLAY CRC32 OF 1ST OR 2ND 512K ROM.
+;
 ; OPTION (H) - DEBUG OPTION - SWITCH ON CPU CLOCK DIVIDER ON SBC-V2-004+
 ; OPTION (T) - DEBUG OPTION - TEST TIMER FOR 20 SECONDS. * = START AND FINISH
 ;
 ;
-; V.DEV	8/1/2021	PHIL SUMMERS, DIFFICULTYLEVELHIGH@GMAIL.COM
+; V.DEV	13/1/2021	PHIL SUMMERS, DIFFICULTYLEVELHIGH@GMAIL.COM
 ;			b1ackmai1er ON RETROBREWCOMPUTERS.ORG
 ;
 ;
@@ -80,12 +82,14 @@
 ;
 ; MAXIMUM SERIAL SPEED LIMITATIONS
 ;
-;  SBC-V2 UART NO FLOW CONTROL 2MHZ  | 9600
-;  SBC-V2 UART NO FLOW CONTROL 4MHZ  | 19200
-;  SBC-V2 UART NO FLOW CONTROL 5MHZ  | 19200
-;  SBC-V2 UART NO FLOW CONTROL 8MHZ  | 38400
-;  SBC-V2 UART NO FLOW CONTROL 10MHZ | 38400
-;  SBC-V2 USB-FIFO 2MHZ+             | N/A
+;  SBC-V2  UART NO FLOW CONTROL   2MHZ      | 9600
+;  SBC-V2  UART NO FLOW CONTROL   4MHZ      | 19200
+;  SBC-V2  UART NO FLOW CONTROL   5MHZ      | 19200
+;  SBC-V2  UART NO FLOW CONTROL   8MHZ      | 38400
+;  SBC-V2  UART NO FLOW CONTROL   10MHZ     | 38400
+;  SBC-V2  USB-FIFO 2MHZ+                   | N/A
+;  SBC-MK4 ASCI NO FLOW CONTROL   18.432MHZ | 9600
+;  SBC-MK4 ASCI WITH FLOW CONTROL 18.432MHZ | 38400
 ;
 ; ACKNOWLEDGEMENTS:
 ;
@@ -97,6 +101,8 @@
 ; md.asm - ROMWBW memory disk driver
 ; https://github.com/wwarthen/RomWBW/blob/master/Source/HBIOS/md.asm
 ;
+; CRC32 - J.G. HARSTON - mdfs.net/Info/Comp/Comms/CRC32.htm
+;
 ;*****************************************************************************
 ;
 #INCLUDE	"std.asm"
@@ -152,11 +158,8 @@ BSPC:		.EQU	'H'-40h		; ^H = Backspace
 	LD	(SERDEV),A
 ;
 RESTART:
-;	LD	DE,$0000		; SET UP
-;	LD	HL,$0000		; START
-;	CALL	MD_CALBAS		; BANK AND SECTOR
-	LD	DE,$0000
-	LD	(MD_FBAS),DE
+	LD	DE,$0000		; SET UP START
+	LD	(MD_FBAS),DE		; BANK AND SECTOR
 
 	LD	HL,MD_FIDEN		; IDENTIFY CHIP
 	CALL	MD_FNCALL		; AT THIS BANK/SECTOR
@@ -172,7 +175,29 @@ RESTART:
 	ADD	A,A			; TIMOUT DELAY
 	LD	(TmoFct),A		; FACTOR 
 ;
-MENULP:	CALL	MENU			; DISPLAY MENU
+MENULP:	LD	DE,$0000		; ENSURE WE ARE STARTING
+	LD	(MD_FBAS),DE		; AT BANK 0 SECTOR 0
+;
+	LD	HL,msgCRLF
+	CALL	PRTSTR0
+	CALL	MENU			; DISPLAY MENU
+;
+#IF	(XFUDBG)
+	LD	C,'B'
+	CALL	CONOUT
+	LD	A,(MD_BANK)
+	CALL	PRTHEXB
+	LD	C,'S'
+	CALL	CONOUT
+	LD	A,(MD_SECT)
+	CALL	PRTHEXB
+	LD	C,'T'
+	CALL	CONOUT
+	LD	A,(TmoFct)
+	CALL	PRTHEXB
+	LD	C,':'
+	CALL	CONOUT
+#ENDIF
 	CALL	GETINP			; GET SELECTION
 ;
 	CP	'U'			; BEGIN
@@ -195,6 +220,12 @@ MENULP:	CALL	MENU			; DISPLAY MENU
 ;
 	CP	'D'			; DUPLICATE
 	JP	Z,OPTIOND		; FLASH
+;
+	CP	'1'			; CALCULATE
+	JP	Z,OPTION1		; CRC FLASH #1
+;
+	CP	'2'			; CALCULATE
+	JP	Z,OPTION2		; CRC FLASH #2
 ;
 #IF	(XFUDBG)
 	CP	'T'			; TEST TIMEOUT
@@ -233,22 +264,22 @@ GetNewPacket:
 ;
 NPloop:	LD 	B,5 			; 5 SECONDS OF TIMEOUT BEFORE EACH NEW BLOCK
 	CALL	GetCharTmo
-	jp 	NC,NotPacketTimeout
+	JP 	NC,NotPacketTimeout
 ;
 	LD	HL,retrycnt		; REACHED MAX NUMBER OF RETRIES?
 	dec 	(HL)
-	jp 	Z,FAILRT		; YES, PRINT MESSAGE AND EXIT
+	JP 	Z,FAILRT		; YES, PRINT MESSAGE AND EXIT
 ;
 	LD 	C,NAK			; SEND A NAK TO THE UPLOADER
 	CALL	SEROUT
 	JR 	NPloop
 ;
 NotPacketTimeout:
-	cp	EOT			; DID UPLOADER SAY WE'RE FINISHED?
+	CP	EOT			; DID UPLOADER SAY WE'RE FINISHED?
 	JP	Z,Done			; YES, THEN WE'RE DONE
-	cp 	CAN			; UPLOADER WANTS TO FAIL TRANSFER?
-	jp 	Z,FAILCN		; YES, THEN WE'RE ALSO DONE
-	cp	SOH			; DID WE GET A START-OF-NEW-PACKET?
+	CP 	CAN			; UPLOADER WANTS TO FAIL TRANSFER?
+	JP 	Z,FAILCN		; YES, THEN WE'RE ALSO DONE
+	CP	SOH			; DID WE GET A START-OF-NEW-PACKET?
 	JR	NZ,NPloop		; NO, GO BACK AND TRY AGAIN
 ;
 	LD	HL,packet		; SAVE THE RECEIVED CHAR INTO THE...
@@ -285,7 +316,7 @@ GetRestOfPacket:
 	LD	HL,packet+3		; CALCULATE CHECKSUM FROM 128 BYTES OF DATA
 	LD	B,128
 	XOR	A
-csloop:	add	A,(HL)			; JUST ADD UP THE BYTES
+csloop:	ADD	A,(HL)			; JUST ADD UP THE BYTES
 	INC	HL
 	DJNZ	csloop
 ;
@@ -298,8 +329,9 @@ csloop:	add	A,(HL)			; JUST ADD UP THE BYTES
 	SBC	HL,BC                   ; NUMBERS
 	JP	NZ,FAILPN
 ;
-	LD	HL,pktNo		; HAVE WE RECEIVED
-	LD	A,(HL)			; A BLOCK OF 32
+;	LD	HL,pktNo		; HAVE WE RECEIVED
+;	LD	A,(HL)			; A BLOCK OF 32
+	LD	A,C
 	DEC	A			; XMODEM PACKETS?
 	AND	%00011111		; IF YES THEN WERE WE
 	CP	%00011111		; HAVE ENOUGH TO
@@ -308,7 +340,7 @@ csloop:	add	A,(HL)			; JUST ADD UP THE BYTES
 ;
 	OR	A			; EXIT IF WE GOT A
 	JP	NZ,FAILWF		; WRITE VERIFICATION ERROR
-
+;
 	LD	HL,pktNo		; UPDATE THE PACKET COUNTERS
 	INC 	(HL)
 	INC	HL
@@ -328,7 +360,7 @@ Done:	LD	C,ACK			; TELL UPLOADER
 Done1:	LD 	HL,msgSuccess		; BACK TO
 	JR	MSGRS			; MENU
 ;
-FAILTO:	LD	HL,msgTimout		; TIMOUT WAITING 
+FAILTO:	LD	HL,msgTimout		; TIMEOUT WAITING 
 	JR	ERRRX			; FOR CHARACTER
 ;
 FAILWF:	LD	HL,msgFailWrt		; FLASH
@@ -457,7 +489,7 @@ GetCharTmo:
 	CALL	SERST			; IF THERE IS A 
 	OR	A			; CHARACTER AVAILABLE
 	JR 	NZ,GotChrX		; EXIT NOW OTHERWISE POLL
-	PUSH	BC
+GCtmoa:	PUSH	BC
 	LD	BC,255			; C=CONSTANT (255) FOR INNER TIMING LOOP
 TmoFct:	.EQU	$-1			; B=SPEED FACTOR WHICH GETS UPDATED AT START
 GCtmob:	PUSH	BC
@@ -748,7 +780,7 @@ CONIN:	PUSH	HL			; CONSOLE INPUT. WAIT FOR A CHARACTER ADD RETURN IT IN A
 	POP	HL
 	RET
 ;
-PRTHEXB:PUSH	AF				; PRINT HEX BYTE IN A TO CONSOLE
+PRTHEXB:PUSH	AF			; PRINT HEX BYTE IN A TO CONSOLE
 	PUSH	DE
 	CALL	HEXASC
 	LD	C,D
@@ -771,12 +803,111 @@ HEXASC:	LD	D,A
 	LD	D,A
 	RET
 ;
-HEXCONV:AND	0FH				; CONVERT LOW NIBBLE OF A TO ASCII HEX
+HEXCONV:AND	0FH			; CONVERT LOW NIBBLE OF A TO ASCII HEX
 	ADD	A,90H
 	DAA
 	ADC	A,40H
 	DAA
 	RET
+
+OPTION1:LD	HL,$0000
+	LD	(MD_FBAS),HL
+	LD	C,$00
+	JR	CALCCRC
+;
+OPTION2:LD	HL,$1000
+	LD	(MD_FBAS),HL
+	LD	C,$10
+;
+CALCCRC:CALL	COUTON			; TURN ON OUTPUT
+;
+	LD	HL,msgCalc
+	CALL	PRTSTR0
+;
+	LD	HL,$FFFF		; SET THE
+	LD	(CRC),HL		; START CRC
+	LD	(CRC+2),HL		; CONDITION
+
+	LD	B,16			; LOOP THROUGH
+CRCLP1:	PUSH	BC			; 16 BANKS
+	LD	B,8			; LOOP THROUGH
+CRCLP2:	PUSH	BC			; 8 SECTORS
+;
+	PUSH	BC
+	CALL	DISPROG			; DISPLAY PROGRESS
+;
+	LD	IX,sector4k		; READ 
+	LD	HL,MD_FREAD		; A SECTOR
+	CALL	MD_FNCALL
+	CALL	CRC32			; CALCULATE CRC
+	POP	BC
+;
+	LD	A,(MD_SECT)		; POINT
+	ADD	A,$10			; TO NEXT
+	LD	(MD_SECT),A		; SECTOR
+	
+	POP	BC			; NEXT
+	DJNZ	CRCLP2			; SECTOR
+
+	XOR	A			; RESET SECTOR
+	LD	(MD_SECT),A		; START
+
+	LD	HL,MD_BANK		; POINT TO
+	INC	(HL)			; NEXT BANK
+
+	POP	BC			; NEXT 
+	DJNZ	CRCLP1			; BANK
+;
+	LD	HL,msgCRC32		; DISPLAY
+	CALL	PRTSTR0			; RESULT
+	LD	HL,CRC+3
+	LD	B,4
+DISPCRC:LD	A,$FF
+	XOR	(HL)
+	CALL	PRTHEXB
+	DEC	HL
+	DJNZ	DISPCRC
+;
+	JP	MENULP
+;
+CRC32:	LD	IX,sector4k		; CALCULATE
+	LD	BC,4096			; CRC32 OF
+	LD	DE,(CRC)		; EACH SECTOR
+	LD	HL,(CRC+2)
+BYTELP:	PUSH	BC
+	LD	A,(IX)
+	XOR	E
+	LD	B,8
+ROTLP:	SRL	H
+	RR	L
+	RR	D
+	RRA
+	JP	NC,CLEAR
+	LD	E,A
+	LD	A,H
+	XOR	$ED
+	LD	H,A
+	LD	A,L
+	XOR	$B8
+	LD	L,A
+	LD	A,D
+	XOR	$83
+	LD	D,A
+	LD	A,E
+	XOR	$20
+CLEAR:	DEC	B
+	JP	NZ,ROTLP
+	LD	E,A
+	INC	IX
+	POP	BC
+	DEC	BC
+	LD	A,B
+	OR	C
+	JP	NZ,BYTELP
+	LD	(CRC),DE
+	LD	(CRC+2),HL
+
+	RET
 ;
 ;======================================================================
 ; CALCULATE BANK AND ADDRESS DATA FROM MEMORY ADDRESS
@@ -982,14 +1113,16 @@ MD_FREAD_R:				; THIS CODE GETS RELOCATED TO HIGH MEMORY
 	LD	L,D			; ADDRESS
 ;
 	EX	AF,AF'			; PUT DESTINATION BANK IN AF'
-	LD	A,B			; PUT SOURCE BANK IN AF
 ;
 MD_FRD1:
+	LD	A,B			; PUT SOURCE BANK IN AF
 	CALL	HBX_BNKSEL		; READ			; SWITCH TO SOURCE BANK
 	LD	C,(HL)			; BYTE
 ;
 	EX	AF,AF'			; SELECT BANK 		; SWITCH DESTINATION BANK
+	PUSH	AF
 	CALL	HBX_BNKSEL		; TO WRITE
+	POP	AF
 	LD	(IX+0),C		; WRITE BYTE
 	EX	AF,AF'			;			; PUT SOURCE BANK IN AF
 ;
@@ -1031,7 +1164,9 @@ MD_FVE1:
 	LD	A,(HL)			; READ BYTE
 ;
 	EX	AF,AF'			; SELECT BANK			; SWITCH TO RAM BANK
+	PUSH	AF
 	CALL	HBX_BNKSEL		; TO VERIFY AGAINST
+	POP	AF
 	EX	AF,AF'
 ;
 	SUB	(IX+0)			; COMPARE BYTE
@@ -1072,7 +1207,9 @@ MD_FWRIT_R:				; THIS CODE GETS RELOCATED TO HIGH MEMORY
 	LD	L,D			; ADDRESS
 ;
 MD_FWRI1:
+	PUSH	AF
 	CALL	HBX_BNKSEL		; SELECT BANK TO READ
+	POP	AF
 	EX	AF,AF'			; SAVE CURRENT BANK
 ;
 	LD	C,(IX+0)		; READ IN BYTE
@@ -1128,6 +1265,8 @@ msgBank:	.DB	CR,LF,"BANK ",0
 msgUnsupC:	.DB	CR,LF,"FLASH CHIP NOT SUPPORTED",CR,LF,0
 msgReboot:	.DB	CR,LF,"REBOOTING ...",CR,LF,0
 msgCopying:	.DB	CR,LF,"COPYING ...",CR,LF,0
+msgCalc:	.DB	CR,LF,"CALCULATING CRC32 ...",CR,LF,0
+msgCRC32:	.DB	CR,LF,CR,LF,"CRC32 : ",0
 msgFailWrt:	.DB	CR,LF,"FLASH WRITE FAILED",CR,LF,0
 msgFailure:	.DB	CR,LF,"TRANSMISSION FAILED",CR,LF,0
 msgCancel:	.DB	CR,LF,"TRANSMISSION CANCELLED",CR,LF,0
@@ -1138,6 +1277,8 @@ msgBegin:	.DB	CR,LF,"(R) Reboot"
 		.DB	CR,LF,"(U) Begin Update"
 		.DB	CR,LF,"(X) Exit to Rom Loader"
 		.DB	CR,LF,"(D) Duplicate Flash #1 to #2"
+		.DB	CR,LF,"(1) CRC Flash #1"
+		.DB	CR,LF,"(2) CRC Flash #2"
 #IF	(XFUDBG)
 		.DB	CR,LF,"(H) Select half speed"
 		.DB	CR,LF,"(T) Test 20s timeout"
@@ -1150,7 +1291,7 @@ msgYES:		.DB	"YES",0
 msgNO:		.DB	"NO",0
 msgPacErr:	.DB	CR,LF,"PACKET COUNT MISMATCH ERROR",CR,LF,0
 msgChkSum	.DB	CR,LF,"CHECKSUM ERROR",CR,LF,0
-msgRetry	.DB	CR,LF,"ERROR, RETRY COUNT EXCEED",CR,LF,0
+msgRetry	.DB	CR,LF,"ERROR, RETRY COUNT EXCEEDED",CR,LF,0
 msgTimout	.DB	CR,LF,"ERROR, RECEIVE TIMEOUT",CR,LF,0
 ;
 ; Variables
@@ -1168,6 +1309,8 @@ pktNo1c:	.DB 	0 		; Current packet Number 1-complemented
 MD_FBAS		.DW	$FFFF		; CURRENT BANK AND SECTOR
 MD_SECT		.EQU	MD_FBAS		;  BANK BYTE
 MD_BANK		.EQU	MD_FBAS+1	;  SECTOR BYTE
+CRC		.DW	$FFFF		; CRC32
+		.DW	$FFFF
 ;
 packet:		.DB 	0		; SOH
 		.DB	0		; PacketN