ADD	HL,DE	Form the required address in
				this area.

THE 'CHAN-FLAG' SUBROUTINE
The appropriate flags for the different channels are set by this subroutine.

1615	CHAN-FLAG	LD	(CURCHL),HL	The HL register pair holds the
				base address for a particular
				channel.
		RES	4,(FLAGS2)	Signal 'using other than channel
				'K''.
		INC	HL	Step past the output
		INC	HL	and the input addresses and
		INC	HL	make HL point to the
		INC	HL	channel code.
		LD	C,(HL)	Fetch the code.
		LD	HL,+162D	The base address of the 'channel
				code look-up table'.
		CALL	16DC,INDEXER	Index into this table and locate
				the required offset; but return if
		RET	NC	there is not a matching channel
				code.
		LD	D,+00	Pass the offset to the
		LD	E,(HL)	DE register pair.
		ADD	HL,DE	Jump forward to the appropriate
162C	CALL-JUMP	JP	(HL)	flag setting routine.

THE 'CHANNEL CODE LOOK-UP' TABLE

162D	DEFB	4B 06		- channel 'K', offset +06, address 1634
162F	DEFB	53 12		- channel 'S', offset +12, address 1642
1631	DEFB	50 1B		- channel 'P', offset +1B, address 164D
1633	DEFB	00		- end marker.

THE 'CHANNEL 'K' FLAG' SUBROUTINE

1634	CHAN-K	SET	0,(TV-FLAG)	Signal 'using lower screen'.
		RES	5,(FLAGS)	Signal 'ready for a key'.
		SET	4,(FLAGS2)	Signal 'using channel 'K''.
		JR	1646,CHAN-S-1	Jump forward.

THE 'CHANNEL 'S' FLAG' SUBROUTINE

1642	CHAN-S	RES	0,(TV-FLAG)	Signal 'using main screen'.
1646	CHAN-S-1	RES	1,(FLAGS)	Signal 'printer not being used'.
		JP	0D4D,TEMPS	Exit via TEMPS so as to set the
				colour system variables.

THE 'CHANNEL 'P' FLAG' SUBROUTINE
164D	CHAN-P	SET	1,(FLAGS)	Signal 'printer in use'.
		RET

THE 'MAKE-ROOM' SUBROUTINE
This is a very important subroutine.  It is called on many occasions to 'open up' an area.  In all cases the HL register pair points to the location after the place where 'room' is required and the BC register pair holds the length of the 'room' needed.  When a single space only is required then the subroutine is entered at ONE-SPACE.

1652	ONE-SPACE	LD	BC,+0001	Just the single extra location
				is required.
1655	MAKE-ROOM	PUSH	HL	Save the pointer.
		CALL	1F05,TEST-ROOM	Make sure that there is sufficient
				memory available for the task
				being undertaken.
		POP	HL	Restore the pointer.