diff --git a/src/kernal/board_m65/mega65_iec_slow_fast.s b/src/kernal/board_m65/mega65_iec_slow_fast.s
new file mode 100644
index 00000000..310df6e3
--- /dev/null
+++ b/src/kernal/board_m65/mega65_iec_slow_fast.s
@@ -0,0 +1,45 @@
+;; #LAYOUT# M65 KERNAL_0 #TAKE
+;; #LAYOUT# *   *        #IGNORE
+
+;
+; Checks if system is in MEGA65 native mode; if so, switches CPU speed to fast/slow - for IEC routines;
+; Alters only status bits, all remaining registers preserved
+;
+
+!ifdef CONFIG_IEC {
+
+
+m65_iec_slow:
+
+	jsr M65_MODEGET
+	bcs m65_iec_fast_slow_done
+
+	; Switch CPU speed
+
+	pha
+	lda VIC_CTRLB
+	and #%10111111
+	bra m65_iec_fast_slow_common
+
+m65_iec_fast:
+
+	jsr M65_MODEGET
+	bcs m65_iec_fast_slow_done
+
+	pha
+	lda VIC_CTRLB
+	ora #%01000000
+
+	; FALLTROUGH
+
+m65_iec_fast_slow_common:
+
+	sta VIC_CTRLB
+	pla
+
+	; FALLTROUGH
+
+m65_iec_fast_slow_done:
+
+	rts
+}
diff --git a/src/kernal/board_m65/mega65_viciv_init.s b/src/kernal/board_m65/mega65_viciv_init.s
index 91c2131c..e73f635a 100644
--- a/src/kernal/board_m65/mega65_viciv_init.s
+++ b/src/kernal/board_m65/mega65_viciv_init.s
@@ -17,10 +17,10 @@ viciv_init:
 	lda #$00
 	sta MISC_EMU
 
-	; Set misc VIC-IV flags
+	; Set VIC-IV CTRL registers
 
-	lda #%01000000  ; enable C65 character set
-	sta VIC_CTRLA
+	lda #%01000000                     ; enable C65 character set
+	jsr mega65_viciv_setctrl_AC        ; also initialize remaining CTRLA / CTRLC bits; CTRLB will be set by screen editor
 
 	; Disable hot registers
 
diff --git a/src/kernal/board_m65/mega65_viciv_setctrl_AC.s b/src/kernal/board_m65/mega65_viciv_setctrl_AC.s
new file mode 100644
index 00000000..c49f31de
--- /dev/null
+++ b/src/kernal/board_m65/mega65_viciv_setctrl_AC.s
@@ -0,0 +1,18 @@
+;; #LAYOUT# M65 KERNAL_0 #TAKE
+;; #LAYOUT# *   *        #IGNORE
+
+;
+; Helper routine for setting VIC-IV control registers A and C
+;
+
+
+mega65_viciv_setctrl_AC:
+
+	sta VIC_CTRLA
+
+	lda VIC_CTRLC
+	and #%01101000
+	ora #%01000000  ; make C65/C128 fast modes switch to max MEGA65 CPU speed
+	sta VIC_CTRLC
+
+	rts
diff --git a/src/kernal/board_m65/mega65_viciv_shutdown.s b/src/kernal/board_m65/mega65_viciv_shutdown.s
index 0a4492a5..38cc0067 100644
--- a/src/kernal/board_m65/mega65_viciv_shutdown.s
+++ b/src/kernal/board_m65/mega65_viciv_shutdown.s
@@ -20,12 +20,8 @@ viciv_shutdown:
 	; Set misc VIC-IV flags
 
 	lda #%00000000
-	sta VIC_CTRLA  ; enable C64 character set
-	sta VIC_CTRLB  ; disable extended resolution and attributes
-
-	lda VIC_CTRLC
-	and #%00101000 ; disable fast mode and various VIC-IV extensions
-	sta VIC_CTRLC
+	sta VIC_CTRLB                      ; disable extended resolution and attributes, disable 3.5 MHz mode
+	jsr mega65_viciv_setctrl_AC        ; enable C64 character set, initialize remaining CTRLA / CTRLC bits
 
 	; Reenable hot registers
 
diff --git a/src/kernal/errors.s b/src/kernal/errors.s
index 5c021764..917317d7 100644
--- a/src/kernal/errors.s
+++ b/src/kernal/errors.s
@@ -90,5 +90,9 @@ kernalerror_TOP_MEM_RS232:
 
 	lda #K_ERR_TOP_MEM_RS232
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch back to fast mode
+	jsr m65_iec_fast
+}
 	sec
 	rts
diff --git a/src/kernal/extapi_m65/mega65_modeset.s b/src/kernal/extapi_m65/mega65_modeset.s
index 52a04236..4dec329c 100644
--- a/src/kernal/extapi_m65/mega65_modeset.s
+++ b/src/kernal/extapi_m65/mega65_modeset.s
@@ -25,7 +25,7 @@ m65_mode64:
 	jsr viciv_shutdown
 	jsr vicii_init
 
-	; Switch CPU speed back to normal
+	; Switch CPU speed to normal
 
 	lda #$40
 	sta CPU_D6510
@@ -42,9 +42,9 @@ m65_mode65:
 
 	sei
 
-	; Switch CPU speed to fast
+	; Switch CPU speed to normal; VIC-IV register will be used to set the maximum one
 
-	lda #$41
+	lda #$40
 	sta CPU_D6510
 
 	; Set the magic string to mark native mode
diff --git a/src/kernal/iec/iec_return.s b/src/kernal/iec/iec_return.s
index 4bf64b30..bf9972f7 100644
--- a/src/kernal/iec/iec_return.s
+++ b/src/kernal/iec/iec_return.s
@@ -20,9 +20,16 @@ iec_return_success:
 	; BSOUR is certainly not valid anymore
 	lda #$00
 	sta C3PO
+
 	; Restore registers
 	+ply_trash_a
 	+plx_trash_a
+
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch back to fast mode
+	jsr m65_iec_fast
+}
+
 	; Report success
 	clc
 	rts
@@ -31,12 +38,15 @@ iec_return_DEVICE_NOT_FOUND:
 
 	; Set IEC line to normal idle state
 	jsr iec_set_idle
+
 	; BSOUR is certainly not valid anymore
 	lda #$00
 	sta C3PO
+
 	; Restore registers
 	+ply_trash_a
 	+plx_trash_a
+
 	; Report error
 	jmp kernalerror_DEVICE_NOT_FOUND
 }
diff --git a/src/kernal/iec/iec_rx_byte.s b/src/kernal/iec/iec_rx_byte.s
index 32d1deea..fc565c85 100644
--- a/src/kernal/iec/iec_rx_byte.s
+++ b/src/kernal/iec/iec_rx_byte.s
@@ -16,6 +16,11 @@
 
 iec_rx_dispatch:
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_slow
+}
+
 	lda IECPROTO
 	cmp #IEC_JIFFY
 	+beq jiffydos_rx_byte
@@ -27,6 +32,11 @@ iec_rx_dispatch:
 
 iec_rx_byte:
 
+!ifdef CONFIG_MB_M65 { !ifndef CONFIG_IEC_JIFFYDOS {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_slow
+} }
+
 	; Store .X and .Y on the stack - preserve them
 	+phx_trash_a
 	+phy_trash_a
@@ -60,7 +70,7 @@ iec_rx_byte:
 	; For DolphinDOS just fetch the byte from parallel port
 	lda CIA2_PRB
 	pha
-	jmp iec_rx_acknowledge
+	+bra iec_rx_acknowledge
 
 iec_rx_no_dolphindos:
 
@@ -124,7 +134,7 @@ iec_rx_clk_wait2:
 	jsr kernalstatus_EOI
 	pla
 
-	jmp iec_rx_end
+	+bra iec_rx_end
 @2:
 	; More bits?
 	dex
@@ -150,6 +160,11 @@ iec_rx_acknowledge:
 
 iec_rx_end:
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch back to fast mode
+	jsr m65_iec_fast
+}
+
 	+ply_trash_a
 	+plx_trash_a
 	lda TBTCNT
diff --git a/src/kernal/iec/iec_tx_byte.s b/src/kernal/iec/iec_tx_byte.s
index 785859b7..586bda40 100644
--- a/src/kernal/iec/iec_tx_byte.s
+++ b/src/kernal/iec/iec_tx_byte.s
@@ -18,6 +18,12 @@
 iec_tx_dispatch:
 
 	php                                ; preserve C flag for EOI indication
+
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_slow
+}
+
 	lda IECPROTO
 	cmp #IEC_JIFFY
 	bne @1
@@ -34,6 +40,11 @@ iec_tx_dispatch:
 
 iec_tx_byte:
 
+!ifdef CONFIG_MB_M65 { !ifndef CONFIG_IEC_JIFFYDOS {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_slow
+} }
+
 	; Store .X and .Y on the stack - preserve them
 	+phx_trash_a
 	+phy_trash_a
@@ -84,7 +95,7 @@ iec_tx_common:
 	jsr iec_pull_clk_release_data_oneshot
 
 	; Finish the flow
-	jmp iec_tx_common_finalize
+	+bra iec_tx_common_finalize
 
 iec_tx_no_dolphindos:
 
@@ -122,7 +133,7 @@ iec_tx_common_sendbit:
 
 	; Bit is 0
 	jsr iec_release_clk_pull_data
-	jmp iec_tx_common_bit_is_sent
+	+bra iec_tx_common_bit_is_sent
 @4:
 	; Bit is 1
 	jsr iec_release_clk_data
diff --git a/src/kernal/iec_fast/dolphindos_load.s b/src/kernal/iec_fast/dolphindos_load.s
index 4b3487fa..7a8edd07 100644
--- a/src/kernal/iec_fast/dolphindos_load.s
+++ b/src/kernal/iec_fast/dolphindos_load.s
@@ -27,6 +27,11 @@ dolphindos_load:
 	ora #BIT_CIA2_PRA_DAT_OUT
 	sta TBTCNT                         ; pull DATA
 }
+
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_slow
+}
 	; FALLTROUGH
 
 dolphindos_load_loop:
@@ -80,7 +85,7 @@ dolphindos_load_loop:
 	sta IECPROTO
 
 	; End of load loop
-	jmp load_iec_loop_end
+	+bra load_iec_loop_end
 
 dolphindos_load_no_eoi:
 
@@ -103,12 +108,16 @@ dolphindos_load_no_eoi:
 	iny
 	bne dolphindos_load_loop
 	inc EAL+1
-	jmp dolphindos_load_loop
+	+bra dolphindos_load_loop
 
 !ifndef CONFIG_IEC_DOLPHINDOS_FAST {
 
 dolphindos_load_end:
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch back to fast mode
+	jsr m65_iec_fast
+}
 	; Update EAL
 	clc
 	jsr iec_update_EAL_by_Y
diff --git a/src/kernal/iec_fast/jiffydos_load.s b/src/kernal/iec_fast/jiffydos_load.s
index 1eef3b60..fc339414 100644
--- a/src/kernal/iec_fast/jiffydos_load.s
+++ b/src/kernal/iec_fast/jiffydos_load.s
@@ -80,6 +80,10 @@ jiffydos_load:
 	; A trick to shorten EAL update time
 	ldy #$FF
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_fast
+}
 	; FALLTROUGH
 
 jiffydos_load_loop_esc:
@@ -180,6 +184,10 @@ jiffydos_load_end:
 	; A trick to shorten EAL update time
 	ldy #$FF
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch to 1 MHz
+	jsr m65_iec_slow
+}
 	; FALLTROUGH
 
 jiffydos_load_loop:
@@ -257,10 +265,14 @@ jiffydos_load_loop:
 	cpy #$FF
 	bne jiffydos_load_loop
 	inc EAL+1
-	jmp jiffydos_load_loop
+	+bra jiffydos_load_loop
 
 jiffydos_load_end:
 
+!ifdef CONFIG_MB_M65 {
+	; If in native mode, switch back to fast mode
+	jsr m65_iec_fast
+}
 	; Save last byte
 	tax
 
diff --git a/src/kernal/screen_m65/mega65_screen_tables_misc.s b/src/kernal/screen_m65/mega65_screen_tables_misc.s
index f0f6b684..8ec028f6 100644
--- a/src/kernal/screen_m65/mega65_screen_tables_misc.s
+++ b/src/kernal/screen_m65/mega65_screen_tables_misc.s
@@ -4,9 +4,9 @@
 
 m65_scrtab_vic_ctrlb:        ; parameters for VIC control register B
 
-	!byte %00100000 ; 40x25 + extended attributes
-	!byte %10100000 ; 80x25 + extended attributes
-	!byte %10101000 ; 80x50 + extended attributes
+	!byte %01100000 ; 40x25 + extended attributes + VFAST
+	!byte %11100000 ; 80x25 + extended attributes + VFAST
+	!byte %11101000 ; 80x50 + extended attributes + VFAST
 
 m65_scrtab_colviewmax_lo:       ; maximum allowed color viewport start - low byte