diff --git a/src/zvm_m65/debug.s b/src/zvm_m65/debug.s
new file mode 100644
index 00000000..9f39401a
--- /dev/null
+++ b/src/zvm_m65/debug.s
@@ -0,0 +1,82 @@
+
+
+DBG_print_PC_opcode:
+
+	php
+	pha
+	phx
+	phy
+	phz
+
+	pha
+
+	jsr PRIMM
+	!pet $0D, "PC: ", 0
+
+	dew REG_PC
+	lda REG_PC+1
+	jsr DBGINT_print_hex_byte	
+	lda REG_PC+0
+	jsr DBGINT_print_hex_byte	
+	inw REG_PC
+
+	jsr PRIMM
+	!pet " opcode: ", 0
+
+	pla
+@1:
+	beq @1
+	jsr DBGINT_print_hex_byte
+
+	; FALLTROUGH
+
+DBGINT_end:
+
+	plz
+	ply
+	plx
+	pla
+	plp
+
+	rts
+
+
+DBG_print_hex:
+
+	php
+	pha
+	phx
+	phy
+	phz
+
+	pha
+	lda #' '
+	jsr CHROUT
+	pla
+	jsr DBGINT_print_hex_byte
+	jmp DBGINT_end
+
+
+
+
+DBGINT_print_hex_byte:
+
+	pha
+	lsr
+	lsr
+	lsr
+	lsr
+	ora #$30
+	cmp #$3A
+	bcc @1
+	adc #6
+@1:	
+	jsr CHROUT
+	pla
+	and #$0f
+	ora #$30
+	cmp #$3A
+	bcc @2
+	adc #6
+@2:
+	jmp CHROUT
diff --git a/src/zvm_m65/z80_dispatch.s b/src/zvm_m65/z80_dispatch.s
index ee6baebf..9d0132fc 100644
--- a/src/zvm_m65/z80_dispatch.s
+++ b/src/zvm_m65/z80_dispatch.s
@@ -8,6 +8,9 @@
 	; Fetch and execute next opcode
 
 	+Z80_FETCH_VIA_PC_INC
+
+	; jsr DBG_print_PC_opcode
+
 	asl
 	tax
 	bcs @1
diff --git a/src/zvm_m65/zvm_cputest.s b/src/zvm_m65/zvm_cputest.s
index dc15ab24..157e507c 100644
--- a/src/zvm_m65/zvm_cputest.s
+++ b/src/zvm_m65/zvm_cputest.s
@@ -8,6 +8,7 @@ ZVM_cputest:
 
 	; XXX move loading code to separate routine(s)
 
+
 	; Copy file name to RAM
 
 	ldx #$FF
@@ -30,7 +31,7 @@ ZVM_cputest:
 
 	; Try to find the file
 
-	lda #$34
+	lda #$34                           ; dos_findfile
 	sta HTRAP00
 	+nop
 	+bcc @end
@@ -38,13 +39,15 @@ ZVM_cputest:
 	jsr PRIMM
 	!pet "Loading Z80TEST.COM", 0
 
-	; Open the file
+	; Close all the files, to make sure handle is available
 
-	lda #$00
+	lda #$22                          ; dos_closeall
 	sta HTRAP00
 	+nop
-	
-	lda #$18
+
+	; Open the file
+
+	lda #$18                          ; dos_openfile
 	sta HTRAP00
 	+nop
 
@@ -55,9 +58,9 @@ ZVM_cputest:
 
 	; Prepare pointers
 
-	lda #$FF
+	lda #$0F
 	sta BIOS_IOBUFERPTR+3
-	lda #$D6
+	lda #$FD
 	sta BIOS_IOBUFERPTR+2
 
 	lda #$00                                     ; $0005:0100 - from CP/M point of view this is start of page 1 in bank 1 
@@ -89,7 +92,7 @@ ZVM_cputest:
 
 	; Read up to 512 bytes
 
-	lda #$1A
+	lda #$1A                                     ; dos_readfile
 	sta HTRAP00
 	+nop
 
@@ -123,7 +126,7 @@ ZVM_cputest:
 
 	; Close the file
 
-	lda #$20
+	lda #$20                                     ; dos_closefile
 	sta HTRAP00
 	+nop