Volex TTX2000 S Issue 1.2: Routine at 029D

029D: decode_packet_number: Get the packet address from the Magazine Row Address Group.

Used by the routine at NMI_ISR.
decode_packet_number	029D	CALL hamming_decode_hl	Hamming 8/4 decode the byte at address in HL.
	02A0	LD A,B	Return if result is $FF.
	02A1	CP $FF
	02A3	RET Z
	02A4	AND $08	Else copy bit 3 of result into bit 0 of E.
	02A6	RRCA
	02A7	RRCA
	02A8	RRCA
	02A9	LD E,A
	02AA	INC HL	Hamming 8/4 decode the next byte.
	02AB	CALL hamming_decode_hl	Hamming 8/4 decode the next byte.
	02AE	LD A,B	Return if result is $FF.
	02AF	CP $FF
	02B1	RET Z
	02B2	AND A	Else shift result left and add E.
	02B3	RLCA
	02B4	ADD A,E
	02B5	LD B,A	Return resulting packet number in B.
	02B6	RET	Return resulting packet number in B.