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>