THE SCREEN & PRINTER HANDLING ROUTINES

THE 'PRINT-OUT' ROUTINES
All of the printing to the main part of the screen, the lower part of the screen and the printer is handled by this set of routines.
The PRINT-OUT routine is entered with the A register holding the code for a control character, a printable character or a token.

09F4	PRINT-OUT	CALL	0B03,PO-FETCH	The current print position.
		CP	+20	If the code represents a
		JP	NC,0AD9,PO-ABLE	printable character then jump.
		CP	+06	Print a question mark for
		JR	C,0A69,PO-QUEST	codes in the range +00 - +05.
		CP	+18	And also for codes +18 - +1F.
		JR	NC,0A69,PO-QUEST
		LD	HL,+0A0B	Base of 'control' table.
		LD	E,A	Move the code to the
		LD	D,+00	DE register pair.
		ADD	HL,DE	Index into the table and
		LD	E,(HL)	fetch the offset.
		ADD	HL,DE	Add the offset and make
		PUSH	HL	an indirect jump to the
		JP	0B03,PO-FETCH	appropriate subroutine.

THE 'CONTROL CHARACTER' TABLE

address	offset	character	address	offset	character

0A11	4E	PRINT comma	0A1A	4F	not used
0A12	57	EDIT	0A1B	5F	lNK control
0A13	10	cursor left	0A1C	5E	PAPER control
0A14	29	cursor right	0A1D	5D	FLASH control
0A15	54	cursor down	0A1E	5C	BRlGHT control
0A16	53	cursor up	0A1F	5B	INVERSE control
0A17	52	DELETE	0A20	5A	OVER control
0A18	37	ENTER	0A21	54	AT control
0A19	50	not used	0A22	53	TAB control

THE 'CURSOR LEFT' SUBROUTINE
The subroutine is entered with the B register holding the current line number and the C register with the current column number.

0A23	PO-BACK-1	INC	C	Move leftwards by one column.
		LD	A,+22	Accept the change unless
		CP	C	up against the lefthand side.
		JR	NZ,0A3A,PO-BACK-3
		BIT	1,(FLAGS)	If dealing with the printer
		JR	NZ,0A38,PO-BACK-2	jump forward.
		INC	B	Go up one line.
		LD	C,+02	Set column value.
		LD	A,+18	Test against top line.
		CP	B	Note: This ought to be +19.
		JR	NZ,0A3A,PO-BACK-3	Accept the change unless at
				the top of the screen.
		DEC	B	Unacceptable so down a line.
0A38	PO-BACK-2	LD	C,+21	Set to lefthand column.
0A3A	PO-BACK-3	JP	0DD9,CL-SET	Make an indirect return via
				CL-SET & PO-STORE.

THE 'CURSOR RIGHT' SUBROUTINE
This subroutine performs an operation identical to the BASIC statement - PRINT
OVER 1;CHR$ 32; -.

0A3D	PO-RIGHT	LD	A,(P-FLAG)	Fetch P-FLAG and save it on
		PUSH	AF	the machine stack.