;
; CRC16 calculation module
;
	.globl 	_crc_value
	.globl 	_crc16
	.equ	BANK, 0x96
;	.equ	DPS, 0x86
; Variable in XMEM holding current CRC16 value, being updated
	.area XSEG    (XDATA)
_crc_value::
	.ds 2

;-------------------------------------------------------
; CRC16 subroutine
; - dptr points to byte to be CRCd in xmem
; - algorithm uses table lookup
;-------------------------------------------------------
	.area HOME    (CODE)
	.area CSEG    (CODE)
;	.area BANK1   (CODE)
_crc16:
	mov	BANK, #1
	push	dph
	push	dpl
	movx	a, @dptr
;	inc	DPS
	mov	b, a
	mov	dptr, #_crc_value
	movx	a, @dptr

	xrl	a, b 			; create index into tables
	push	a 			; save index
	mov	dptr, #crc16_table_l 	; low part of table address
	movc	a, @a+dptr		; get low byte
	mov	b, a

	mov	dptr, #_crc_value + 1
	movx	a, @dptr

	xrl	a, b
	mov	dptr, #_crc_value
	movx	@dptr, a		; save result low part
	mov	dptr, #crc16_table_h	; high part of table address
	pop	a			; restore index
	movc	a, @a+dptr
	mov	dptr, #_crc_value+1
	movx	@dptr, a		; save result high part
	pop	dpl
	pop	dph
;	clr	DPS
	ret

	.area BANK1   (CODE)

crc16_table_l:
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x00, #0xc1, #0x81, #0x40, #0x01, #0xc0, #0x80, #0x41
	.byte #0x01, #0xc0, #0x80, #0x41, #0x00, #0xc1, #0x81, #0x40

crc16_table_h:
	.byte #0x00, #0xc0, #0xc1, #0x01, #0xc3, #0x03, #0x02, #0xc2
	.byte #0xc6, #0x06, #0x07, #0xc7, #0x05, #0xc5, #0xc4, #0x04
	.byte #0xcc, #0x0c, #0x0d, #0xcd, #0x0f, #0xcf, #0xce, #0x0e
	.byte #0x0a, #0xca, #0xcb, #0x0b, #0xc9, #0x09, #0x08, #0xc8
	.byte #0xd8, #0x18, #0x19, #0xd9, #0x1b, #0xdb, #0xda, #0x1a
	.byte #0x1e, #0xde, #0xdf, #0x1f, #0xdd, #0x1d, #0x1c, #0xdc
	.byte #0x14, #0xd4, #0xd5, #0x15, #0xd7, #0x17, #0x16, #0xd6
	.byte #0xd2, #0x12, #0x13, #0xd3, #0x11, #0xd1, #0xd0, #0x10
	.byte #0xf0, #0x30, #0x31, #0xf1, #0x33, #0xf3, #0xf2, #0x32
	.byte #0x36, #0xf6, #0xf7, #0x37, #0xf5, #0x35, #0x34, #0xf4
	.byte #0x3c, #0xfc, #0xfd, #0x3d, #0xff, #0x3f, #0x3e, #0xfe
	.byte #0xfa, #0x3a, #0x3b, #0xfb, #0x39, #0xf9, #0xf8, #0x38
	.byte #0x28, #0xe8, #0xe9, #0x29, #0xeb, #0x2b, #0x2a, #0xea
	.byte #0xee, #0x2e, #0x2f, #0xef, #0x2d, #0xed, #0xec, #0x2c
	.byte #0xe4, #0x24, #0x25, #0xe5, #0x27, #0xe7, #0xe6, #0x26
	.byte #0x22, #0xe2, #0xe3, #0x23, #0xe1, #0x21, #0x20, #0xe0
	.byte #0xa0, #0x60, #0x61, #0xa1, #0x63, #0xa3, #0xa2, #0x62
	.byte #0x66, #0xa6, #0xa7, #0x67, #0xa5, #0x65, #0x64, #0xa4
	.byte #0x6c, #0xac, #0xad, #0x6d, #0xaf, #0x6f, #0x6e, #0xae
	.byte #0xaa, #0x6a, #0x6b, #0xab, #0x69, #0xa9, #0xa8, #0x68
	.byte #0x78, #0xb8, #0xb9, #0x79, #0xbb, #0x7b, #0x7a, #0xba
	.byte #0xbe, #0x7e, #0x7f, #0xbf, #0x7d, #0xbd, #0xbc, #0x7c
	.byte #0xb4, #0x74, #0x75, #0xb5, #0x77, #0xb7, #0xb6, #0x76
	.byte #0x72, #0xb2, #0xb3, #0x73, #0xb1, #0x71, #0x70, #0xb0
	.byte #0x50, #0x90, #0x91, #0x51, #0x93, #0x53, #0x52, #0x92
	.byte #0x96, #0x56, #0x57, #0x97, #0x55, #0x95, #0x94, #0x54
	.byte #0x9c, #0x5c, #0x5d, #0x9d, #0x5f, #0x9f, #0x9e, #0x5e
	.byte #0x5a, #0x9a, #0x9b, #0x5b, #0x99, #0x59, #0x58, #0x98
	.byte #0x88, #0x48, #0x49, #0x89, #0x4b, #0x8b, #0x8a, #0x4a
	.byte #0x4e, #0x8e, #0x8f, #0x4f, #0x8d, #0x4d, #0x4c, #0x8c
	.byte #0x44, #0x84, #0x85, #0x45, #0x87, #0x47, #0x46, #0x86
	.byte #0x82, #0x42, #0x43, #0x83, #0x41, #0x81, #0x80, #0x40