LD	A,B	The 'scroll number' is fetched.

The lower part of the screen is now scrolled 'A' number of times.

0D1C	PO-SCR-4A	PUSH	AF	Save the 'number'.
		LD	HL,+5C6B	This is DF-SZ.
		LD	B,(HL)	The value in DF-SZ is
		LD	A,B	incremented; the B register
		INC	A	set to hold the former value and
		LD	(HL),A	the A register the new value.
		LD	HL,+5C89	This is S-POSN-hi.
		CP	(HL)	The jump is taken if only the
		JR	C,0D2D,PO-SCR-4B	lower part of the display is
				to be scrolled. (B = old DF-SZ).
		INC	(HL)	Otherwise S-POSN-hi is
		LD	B,+18	incremented and the whole
				display scrolled. (B = +18)
0D2D	PO-SCR-4B	CALL	0E00,CL-SCROLL	Scroll 'B' lines.
		POP	AF	Fetch and decrement the
		DEC	A	scroll number'.
		JR	NZ,0D1C,PO-SOR-4A	Jump back until finished.
		POP	HL	Restore the value of
		LD	(P-FLAG),L	P-FLAG.
		POP	HL	Restore the values of ATTR-T
		LD	(ATTR-T),HL	and MASK-T.
		LD	BC,(S-POSN)	In case S-POSN has been
		RES	0,(TV-FLAG)	changed CL-SET is called to
		CALL	0DD9,CL-SET	give a matching value to DF-CC.
		SET	0,(TV-FLAG)	Reset the flag to indicate that
		POP	BC	the lower screen is being
		RET		handled, fetch the line and
				column numbers, and then
				return.

THE 'TEMPORARY COLOUR ITEMS' SUBROUTINE
This is a most important subroutine. It is used whenever the 'permanent' details are required to be copied to the 'temporary' system variables. First ATTR-T & MASK-T are considered

0D4D	TEMPS	XOR	A	A is set to hold +00.
		LD	HL,(ATTR-P)	The current values of ATTR-P
		BIT	0,(TV-FLAG)	and MASK-P are fetched.
		JR	Z,0D5B,TEMPS-1	Jump forward if handing the
				main part of the screen.
		LD	H,A	Otherwise use +00 and the
		LD	L,(BORDCR)	value in BORDCR instead.
0D5B	TEMPS-1	LD	(ATTR-T),HL	Now set ATTR-T & MASK-T.

Next P-FLAG is considered.
		LD	HL,+5C91	This is P-FLAG.
		JR	NZ,0D65,TEMPS-2	Jump forward if dealing with
				the lower part of the screen
				(A = +00).
		LD	A,(HL)	Otherwise fetch the value of
		RRCA		P-FLAG and move the odd bits
				to the even bits.
0D65	TEMPS-2	XOR	(HL)	Proceed to copy the even bits
		AND	+55	of A to P-FLAG.
		XOR	(HL)
		LD	(HL),A
		RET

THE 'CLS COMMAND' ROUTINE
In the first instance the whole of the display is 'cleared' - the 'pixels' are all reset and the attribute bytes are set to equal the value in ATTR-P - then the lower part of the display is reformed.