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+This is a very simple routine that converts an 8-bit integer to the corresponding hexadecimal representation, which is output as a null-terminated string. Multiple calls to the routine can be chained, to convert longer integers. An example is provided to hexify your current IRQ vector (16-bit).
+The null-termination is a bit awkward with the iny/dey that gets executed twice even for every call, but the routine must preserve the index, which has to be initialized to either zero or to the length of an existing string if you want to add this output, mimicing sprintf operation.
+Alternatively, you could relocate the ldy #0 instruction to the beginning of the hexify routine, if you always only convert single bytes. If you should want to print a 3-digit hex number, increment the dst pointer before calling print, and this will omit the first digit.
+Bring in the code for the print routine from [[String manipulation routines]]. When you assemble and run the program (with SYS 8192) it will print the hexadecimal address to the IRQ routine that is currently running on your system and it will normally be EA31.
+<code>
+; Integer to Hex String conversion routine by FMan/Tropyx
+	!to "inttostr.prg",cbm		; use ACME
+; example how to print a 16-bit value in hexadecimal
+	dst = $64	; output string pointer
+	*=$2000
+	lda #0
+	sta dst
+	lda #$7f
+	sta dst+1
+	ldy #0		; initialize string index
+	lda $315
+	jsr hexify	; convert the MSB first
+	lda $314
+	jsr hexify
+	jsr print	; see note above
+	rts
+; this routine converts the given value into a two-digit hex code
+; inputs: A=byte, Y=index - outputs: to given buffer - preserves Y
+hexify	tax
+	lsr
+	lsr
+	lsr
+	lsr
+	jsr hexc	; convert upper nybble
+	jsr output
+	txa
+	and #$f		; convert lower nybble
+	jsr hexc
+output	sta (dst),y	; output a byte using a zp-ptr and Y-index
+incaddr	iny		; increment the output address
+	iny
+	lda #0		; null-terminate the string
+	sta (dst),y
+	dey
+outpa	rts
+hexc	cmp #$a		; subroutine converts 0-F to a character
+	bcs hexa
+	clc		; digit 0-9
+	adc #48
+	bne hexb	; unconditional jump coz Z=FALSE always
+hexa	clc
+	adc #55		; digit A-F
+hexb	rts
+</code>