diff --git a/Source/HBIOS/Config/RCZ80_skz.asm b/Source/HBIOS/Config/RCZ80_skz.asm
index 6b9685c1..df31fe70 100644
--- a/Source/HBIOS/Config/RCZ80_skz.asm
+++ b/Source/HBIOS/Config/RCZ80_skz.asm
@@ -31,4 +31,10 @@
 LEDENABLE	.SET	TRUE		; ENABLES STATUS LED (SINGLE LED)
 LEDPORT		.SET	$6E		; STATUS LED PORT ADDRESS
 ;
+SKZENABLE	.SET	TRUE		; ENABLE SERGEY'S Z80-512K FEATURES
+SKZDIV		.SET	DIV_12		; UART CLK (CLK2) DIVIDER FOR Z80-512K
+;
 WDOGMODE	.SET	WDOG_SKZ	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
+;
+SIO0BCLK	.SET	CPUOSC / 12	; SIO 0B: OSC FREQ IN HZ, ZP=2457600/4915200, RC/SMB=7372800
+SIO0BCFG	.SET	SER_38400_8N1	; SIO 0B: SERIAL LINE CONFIG
diff --git a/Source/HBIOS/cfg_dyno.asm b/Source/HBIOS/cfg_dyno.asm
index 3a2bdbb3..165735cd 100644
--- a/Source/HBIOS/cfg_dyno.asm
+++ b/Source/HBIOS/cfg_dyno.asm
@@ -50,6 +50,8 @@ CTCENABLE	.EQU	FALSE		; ENABLE ZILOG CTC SUPPORT
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	FALSE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_ezz80.asm b/Source/HBIOS/cfg_ezz80.asm
index 7ed162c4..59fcc3d9 100644
--- a/Source/HBIOS/cfg_ezz80.asm
+++ b/Source/HBIOS/cfg_ezz80.asm
@@ -52,6 +52,8 @@ CTCOSC		.EQU	921600		; CTC CLOCK FREQUENCY
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_EZZ80	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 WDOGIO		.EQU	$6F		; WATCHDOG REGISTER ADR
 ;
diff --git a/Source/HBIOS/cfg_master.asm b/Source/HBIOS/cfg_master.asm
index 1c35d567..000aae57 100644
--- a/Source/HBIOS/cfg_master.asm
+++ b/Source/HBIOS/cfg_master.asm
@@ -74,6 +74,9 @@ CTCOSC		.EQU	614400		; CTC CLOCK FREQUENCY
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+SKZDIV		.EQU	DIV_1		; UART CLK (CLK2) DIVIDER FOR Z80-512K
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 WDOGIO		.EQU	$6F		; WATCHDOG REGISTER ADR
 ;
diff --git a/Source/HBIOS/cfg_mk4.asm b/Source/HBIOS/cfg_mk4.asm
index 7f696d2d..98e8f43b 100644
--- a/Source/HBIOS/cfg_mk4.asm
+++ b/Source/HBIOS/cfg_mk4.asm
@@ -53,6 +53,8 @@ CTCTIMER	.EQU	FALSE		; ENABLE CTC PERIODIC TIMER
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	FALSE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_n8.asm b/Source/HBIOS/cfg_n8.asm
index 7a019536..cf4df4cb 100644
--- a/Source/HBIOS/cfg_n8.asm
+++ b/Source/HBIOS/cfg_n8.asm
@@ -56,6 +56,8 @@ CTCTIMER	.EQU	FALSE		; ENABLE CTC PERIODIC TIMER
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	FALSE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_rcz180.asm b/Source/HBIOS/cfg_rcz180.asm
index 5715bf98..71eb061f 100644
--- a/Source/HBIOS/cfg_rcz180.asm
+++ b/Source/HBIOS/cfg_rcz180.asm
@@ -53,6 +53,8 @@ CTCTIMER	.EQU	FALSE		; ENABLE CTC PERIODIC TIMER
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	TRUE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_rcz280.asm b/Source/HBIOS/cfg_rcz280.asm
index b751119b..6e37b3e4 100644
--- a/Source/HBIOS/cfg_rcz280.asm
+++ b/Source/HBIOS/cfg_rcz280.asm
@@ -56,6 +56,8 @@ CTCOSC		.EQU	7372800		; CTC CLOCK FREQUENCY
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	TRUE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_rcz80.asm b/Source/HBIOS/cfg_rcz80.asm
index 73c2c0fa..5a7418d3 100644
--- a/Source/HBIOS/cfg_rcz80.asm
+++ b/Source/HBIOS/cfg_rcz80.asm
@@ -52,6 +52,9 @@ CTCOSC		.EQU	CPUOSC		; CTC CLOCK FREQUENCY
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+SKZDIV		.EQU	DIV_1		; UART CLK (CLK2) DIVIDER FOR Z80-512K
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 WDOGIO		.EQU	$6E		; WATCHDOG REGISTER ADR
 ;
diff --git a/Source/HBIOS/cfg_sbc.asm b/Source/HBIOS/cfg_sbc.asm
index 28112b4c..f521de2b 100644
--- a/Source/HBIOS/cfg_sbc.asm
+++ b/Source/HBIOS/cfg_sbc.asm
@@ -50,6 +50,8 @@ CTCOSC		.EQU	614400		; CTC CLOCK FREQUENCY
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	FALSE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_scz180.asm b/Source/HBIOS/cfg_scz180.asm
index d28e02f3..c61505cb 100644
--- a/Source/HBIOS/cfg_scz180.asm
+++ b/Source/HBIOS/cfg_scz180.asm
@@ -48,6 +48,8 @@ CTCTIMER	.EQU	FALSE		; ENABLE CTC PERIODIC TIMER
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	TRUE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_zeta.asm b/Source/HBIOS/cfg_zeta.asm
index 89fd4521..3157c38c 100644
--- a/Source/HBIOS/cfg_zeta.asm
+++ b/Source/HBIOS/cfg_zeta.asm
@@ -42,6 +42,8 @@ CTCENABLE	.EQU	FALSE		; ENABLE ZILOG CTC SUPPORT
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	FALSE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/cfg_zeta2.asm b/Source/HBIOS/cfg_zeta2.asm
index e2281788..62363c33 100644
--- a/Source/HBIOS/cfg_zeta2.asm
+++ b/Source/HBIOS/cfg_zeta2.asm
@@ -53,6 +53,8 @@ CTCOSC		.EQU	921600		; CTC CLOCK FREQUENCY
 ;
 EIPCENABLE	.EQU	FALSE		; EIPC: ENABLE Z80 EIPC (Z84C15) INITIALIZATION
 ;
+SKZENABLE	.EQU	FALSE		; ENABLE SERGEY'S Z80-512K FEATURES
+;
 WDOGMODE	.EQU	WDOG_NONE	; WATCHDOG MODE: WDOG_[NONE|EZZ80|SKZ]
 ;
 DIAGENABLE	.EQU	FALSE		; ENABLES OUTPUT TO 8 BIT LED DIAGNOSTIC PORT
diff --git a/Source/HBIOS/hbios.asm b/Source/HBIOS/hbios.asm
index 7e83c516..458973df 100644
--- a/Source/HBIOS/hbios.asm
+++ b/Source/HBIOS/hbios.asm
@@ -1424,6 +1424,17 @@ HB_CPU1:
 	CALL	DSRTC_PREINIT
 #ENDIF
 ;
+#IF (SKZENABLE)
+;
+	; SET THE SK Z80-512K UART CLK2 DIVIDER AS
+	; CONFIGURED.  NOTE THAT THIS IMPLICITLY
+	; CLEARS THE WATCHDOG BIT.  THE WATCHDOG
+	; WILL BE ENABLED LATER IF CONFIGURED.
+	LD	A,SKZDIV	; GET DIVIDER CODE
+	OUT	($6D),A		; IMPLEMENT IT
+;
+#ENDIF
+;
 #IF (CPUFAM == CPU_Z180)
 ;
 	; AT BOOT, Z180 PHI IS OSC / 2
@@ -1971,21 +1982,26 @@ IS_REC_M1:
   #IF (WDOGMODE == WDOG_EZZ80)
 	PRTS("EZZ80$")
   #ENDIF
-;
   #IF (WDOGMODE == WDOG_SKZ)
 	PRTS("SKZ$")
+  #ENDIF
+;
+	PRTS(" IO=0x$")
+	LD	A,WDOGIO
+	CALL	PRTHEXBYTE
+;
+  #IF (WDOGMODE == WDOG_SKZ)
+	; SKZ WATCHDOG IS DISABLED EARLY IN BOOT PROCESS
+	; HERE, WE ONLY NEED TO ENABLE IT, IF APPROPRIATE
 	LD	HL,(HB_TICKS)		; GET LOW WORD
 	LD	A,H			; CHECK FOR
 	OR	L			; ... ZERO
 	JR	Z,HB_WDOFF		; SKIP IF NOT TICKING
 	IN	A,($6D)			; GET PORT VALUE
-	SET	5,A			; SET WDOG ENABLE BIT
-	OUT	($6D),A			; DO IT
+	SET	5,A			; SET THE WATCHDOG ENABLE BIT
+	OUT	($6D),A			; ACTIVATE WATCHDOG
   #ENDIF
 ;
-	PRTS(" IO=0x$")
-	LD	A,WDOGIO
-	CALL	PRTHEXBYTE
 	PRTS(" ENABLED$")
 	JR	HB_WDZ
 ;
diff --git a/Source/HBIOS/std.asm b/Source/HBIOS/std.asm
index 3146c287..9c625aad 100644
--- a/Source/HBIOS/std.asm
+++ b/Source/HBIOS/std.asm
@@ -246,6 +246,42 @@ SER_BAUD1843200	.EQU	$1D << 8
 SER_BAUD3686400	.EQU	$1E << 8
 SER_BAUD7372800	.EQU	$1F << 8
 ;
+; UART DIVIDER VALUES
+; STORED AS 5 BITS: YXXXX
+;
+DIV_1		.EQU	$00
+DIV_2		.EQU	$01
+DIV_4		.EQU	$02
+DIV_8		.EQU	$03
+DIV_16		.EQU	$04
+DIV_32		.EQU	$05
+DIV_64		.EQU	$06
+DIV_128		.EQU	$07
+DIV_256		.EQU	$08
+DIV_512		.EQU	$09
+DIV_1024	.EQU	$0A
+DIV_2048	.EQU	$0B
+DIV_4096	.EQU	$0C
+DIV_8192	.EQU	$0D
+DIV_16384	.EQU	$0E
+DIV_32768	.EQU	$0F
+DIV_3		.EQU	$10
+DIV_6		.EQU	$11
+DIV_12		.EQU	$12
+DIV_24		.EQU	$13
+DIV_48		.EQU	$14
+DIV_96		.EQU	$15
+DIV_192		.EQU	$16
+DIV_384		.EQU	$17
+DIV_768		.EQU	$18
+DIV_1536	.EQU	$19
+DIV_3072	.EQU	$1A
+DIV_6144	.EQU	$1B
+DIV_12288	.EQU	$1C
+DIV_24576	.EQU	$1D
+DIV_49152	.EQU	$1E
+DIV_98304	.EQU	$1F
+;
 SER_XON		.EQU	1 << 6
 SER_DTR		.EQU	1 << 7
 SER_RTS		.EQU	1 << 13
diff --git a/Source/ver.inc b/Source/ver.inc
index 43d00b14..a06edde1 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.44"
+#DEFINE BIOSVER	"3.1.1-pre.45"
diff --git a/Source/ver.lib b/Source/ver.lib
index e8f1e73e..d9f12158 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.44"
+	db	"3.1.1-pre.45"
 	endm