FAP's second hello world program

helloword2.z80

vram_char_base_addr	.equ	0x8000
vram_attri_base_addr	.equ	0x8960

	org	0x0	
	xor	b
	xor	c	
	xor	d
	xor	e
	ld	sp, 0x7fff

	call	disable_vram_copy
	
	; clear screen
	ld	de, 2400
	ld 	b, 0
	ld	c, 0
clear:	call	print
	dec	de
	ld	a,d
	or 	e	
	jp	nz,clear

	; now print "Hello World!" in white (0x3f)
	ld	de, 1
	ld	b, 0x3f

	ld 	c, 'H'
	call	print
	inc	de

	ld 	c, 'e'
	call	print
	inc	de

	ld 	c, 'l'
	call	print
	inc	de

	ld 	c, 'l'
	call	print
	inc	de

	ld 	c, 'o'
	call	print
	inc	de

	inc	de

	ld 	c, 'W'
	call	print
	inc	de

	ld 	c, 'o'
	call	print
	inc	de

	ld 	c, 'r'
	call	print
	inc	de

	ld 	c, 'l'
	call	print
	inc	de

	ld 	c, 'd'
	call	print
	inc	de

	ld 	c, '!'
	call	print
	inc	de

	call	enable_vram_copy

end:	jp	end	

enable_vram_copy:
	ld	hl, 0x92c1
	ld	(hl), 0xff
	ret

disable_vram_copy:
	ld	hl, 0x92c1
	ld	(hl), 0x0
	ret

;	print character
;	c: char
;	b: attri
;	de: char index
;	destories: b, c, d, e, hl
print:
	ld	hl, vram_attri_base_addr
	add	hl, de
	ld	(hl), b

	ld	hl, vram_char_base_addr
	add	hl, de
	ld	(hl), c

	ret