*	convert S19 records to binary data

BUFBEG equ $4000
BUFEND equ $5000

        org $3000

start	sty y_tmp
	ldx #BUFBEG	first character
	ldy #BUFBEG
s19a	ldd ,x
	cmpd #$5331	S1?
	bne done
	ldd 2,x		length
	bsr hex2
	subb #3		don't count addr or cksum
	stb length
	leax 8,x	point .x to data
s1b	ldd ,x++
	bsr hex2
	stb ,y+
	dec length
	bne s1b
	leax 2,x	skip over checksum
s19end	cmpx #BUFEND	past end of buffer?
	bhs done	decode data
	lda ,x+
	cmpa #$20
	blo s19end	skip control characters
	leax -1,x	ungetc printable character
	bra s19a
done	ldy y_tmp
	rts

*	convert 2 ASCII characters in .d to binary number in .b
hex2	bsr hex1	LSNybble
	pshs b
	tfr a,b
	bsr hex1	MSNybble
	lslb
	lslb
	lslb
	lslb
	orb ,s+
	rts
hex1	cmpb #$39
	bls hex1a
	subb #7
hex1a	andb #$0F
	rts

length	rmb 1	length of an s19 record
y_tmp	rmb 2	.y temp storage