The Hobbit (v1.0): Routine at 775E

Scrolls the top 17 character rows of the screen ($4000 onwards, down to $5020) up by one character row, pixel line by pixel line, taking care of the Spectrum's awkward screen layout at the boundaries between the thirds of the screen. The attributes of those rows are scrolled too (so that a picture's colours move with it). Finally the bottom row of the story window at $5020 is cleared by printing 42 spaces in the 6-pixel font.

Scrolls the top 17 character rows of the screen ($4000 onwards, down to $5020) up by one character row, pixel line by pixel line, taking care of the Spectrum's awkward screen layout at the boundaries between the thirds of the screen. The attributes of those rows are scrolled too (so that a picture's colours move with it). Finally the bottom row of the story window at $5020 is cleared by printing 42 spaces in the 6-pixel font.
775E	PUSH AF	Save the registers this uses
775F	PUSH BC
7760	PUSH HL
7761	PUSH DE
7762	LD HL,$4020	HL = the second pixel row of the story window...
7765	LD DE,$4000	...DE = the first, where it is moving to
7768	LD A,$11	17 character rows make up the whole story window
776A	LD B,$00	17 character rows make up the whole story window
776C	PUSH HL	Save the row addresses
776D	PUSH DE	Save the row addresses
776E	LD C,$08	Eight pixel lines per character row
7770	PUSH HL	Save this pixel line's addresses
7771	PUSH DE
7772	PUSH BC
7773	LD C,$20	32 bytes per pixel line
7775	LDIR	Copy it up
7777	POP BC	Restore the counters
7778	POP DE
7779	POP HL
777A	INC H	Move down to the next pixel line
777B	INC D	Move down to the next pixel line
777C	DEC C	One fewer pixel line to do
777D	JR NZ,$7770	One fewer pixel line to do
777F	POP DE	Restore the row addresses
7780	POP HL	Restore the row addresses
7781	LD C,$20	Move both addresses on to the next character row
7783	ADD HL,BC
7784	EX DE,HL
7785	ADD HL,BC
7786	EX DE,HL
7787	PUSH AF	The screen's odd memory layout means a plain add sometimes lands in the wrong third of the screen, so check and correct that:
7788	LD A,D
7789	AND $07
778B	JR Z,$7791	DE is already fine as it is...
778D	LD A,D	DE is already fine as it is...
778E	ADD A,$07	...otherwise nudge it on to the next third
7790	LD D,A	...otherwise nudge it on to the next third
7791	LD A,H	Do the same correction for HL
7792	AND $07
7794	JR Z,$779A
7796	LD A,H
7797	ADD A,$07
7799	LD H,A
779A	POP AF	Restore AF
779B	DEC A	One fewer character row to do
779C	JR NZ,$776C	One fewer character row to do
779E	LD HL,$5820	The attributes need to move up one row too...
77A1	LD DE,$5800
77A4	LD BC,$0220
77A7	LDIR	...so that a picture's colours scroll along with it
77A9	LD B,$2A	The bottom row is now empty: clear it with 42 spaces, a full line of the 6-pixel font
77AB	LD HL,$5020
77AE	LD C,$01
77B0	LD A,$20
77B2	CALL $77BC
77B5	DJNZ $77B2
77B7	POP DE	Restore the saved registers
77B8	POP HL
77B9	POP BC
77BA	POP AF
77BB	RET