diff --git a/src/kernal/board_crt/crt_init.s b/src/kernal/board_crt/crt_init.s
index 69c07dec..0a02c249 100644
--- a/src/kernal/board_crt/crt_init.s
+++ b/src/kernal/board_crt/crt_init.s
@@ -2,8 +2,69 @@
 ;; #LAYOUT# *   *        #IGNORE
 
 
+; Register meaning according to http://wiki.icomp.de/wiki/Retro_Replay
+;
+; $DE00 - write:
+; bit 7 - bit 15 of ROM bank address
+; bit 6 - needed by freeze, not useful for Open ROMs
+; bit 5 - 0 = ROM, 1 = RAM
+; bit 4 - bit 14 of ROM/RAM bank address
+; bit 3 - bit 13 of ROM/RAM bank address
+; bit 2 - 1 = disable cartridge
+; bit 1 - EXROM, 0 = assert
+; bit 0 - GAME, 0 = assert
+;
+; $DE01 - write:
+; bit 7 - bit 15 of ROM bank address
+; bit 6 - 1 = REU compatible memory map
+; bit 5 - needed by flash mode, not useful for Open ROMs
+; bit 4 - bit 14 of ROM/RAM bank address
+; bit 3 - bit 13 of ROM/RAM bank address
+; bit 2 - NoFreeze, 1 = disable freeze function
+; bit 1 - AllowBank, 1 = enables banking of RAM in $DF00/$DE02 area
+; bit 0 - 1 = enables accessory connector
+;
+; $DE00 / $DE01 - read:
+; bit 7 - bit 15 of ROM bank address
+; bit 6 - 1 = REU compatible memory map
+; bit 5 - needed by flash mode, not useful for Open ROMs
+; bit 4 - bit 14 of ROM/RAM bank address
+; bit 3 - bit 13 of ROM/RAM bank address
+; bit 2 - 1 = FREEZE button pressed
+; bit 1 - AllowBank
+; bit 0 - 1 = flash mode activated by jumper
+
+
 crt_init:
 
-	; XXX !!! provide implementation
+	; Setup the cart
+
+	lda #%01000100           ; REU compatible memory map, no freezing
+	sta $DE01
+
+	; Bank-in the first ROM bank
+
+	lda #%00000000
+	sta $DE00
+
+	; Check if ROM revision matches the cartridge
 	
+	ldy #$FF
+@1:
+	iny
+	lda $E4B9, y            ; Kernal ROM revision address
+	cmp $9FEC, y
+	bne crt_init_fail
+	cmp #$00
+	bne @1
+
+	; Unmap cartridge memory     XXX provide separate map functions
+
+	lda #%00000010
+	sta $DE00
+
 	rts
+
+crt_init_fail:
+
+	+panic P_ERR_ROM_MISMATCH