Chase H.Q.: Routine at FF2C

Services sound each poll via run_title_tune and scans via scan_keyboard_matrix, rejecting and retrying if the scan is an ambiguous multi-row press (NZ from scan_keyboard_matrix) or "no key held" (D still $FF).

Duplicate check ($FF3D-$FF48): compares the new key code against the C-1 entries already stored at $FFF7 (C is the 1-based control index from the caller); a match rejects and loops back to re-scan.

Store ($FF4C-$FF52): the new key code is written to $FFF6+C (i.e. $FFF7 for control 1, ... $FFFE for control 8) -- the growing list used by the duplicate check above and read back by FEE2-$FEF1.

Name lookup ($FF53-$FF68): the scan-matrix key code (bits 0-2 = column/bit-within-row 0-4, bits 3+ = row 0-7, from scan_keyboard_matrix) is unpacked into row and bit, then re-combined as index = 5*bit + row (a column-major layout, not row-major) to index the 2-bytes/entry name table at FF95. Print ($FF6D-$FF7F): the looked-up entry's two characters are copied into a 2-character scratch buffer at $FD97-$FD9B alongside the caller's screen address (DE), with bit 7 forced on the second (the string terminator consumed by print_character's own BIT 7 test -- see FF95: usually a space, but a real second letter for the spelled-out SYMBOL SHIFT/SPACE/ENTER/CAPS SHIFT codes), then print_character prints it. Column advance ($FF82-$FF94): restores the caller's screen address and steps it on by $20 (one label column); on overflow (E wraps past $FF) also bumps D by 8 to drop down a pixel row. The same step is applied unconditionally once more when the caller's remaining loop count B is exactly 4 (FF87-$FF8A) -- the extra step that wraps from the first row of 4 control labels to the second row of 4. Used by the routine at redefine_keys_screen.

Services sound each poll via run_title_tune and scans via scan_keyboard_matrix, rejecting and retrying if the scan is an ambiguous multi-row press (NZ from scan_keyboard_matrix) or "no key held" (D still $FF). Duplicate check ($FF3D-$FF48): compares the new key code against the C-1 entries already stored at $FFF7 (C is the 1-based control index from the caller); a match rejects and loops back to re-scan. Store ($FF4C-$FF52): the new key code is written to $FFF6+C (i.e. $FFF7 for control 1, ... $FFFE for control 8) -- the growing list used by the duplicate check above and read back by FEE2-$FEF1. Name lookup ($FF53-$FF68): the scan-matrix key code (bits 0-2 = column/bit-within-row 0-4, bits 3+ = row 0-7, from scan_keyboard_matrix) is unpacked into row and bit, then re-combined as index = 5*bit + row (a column-major layout, not row-major) to index the 2-bytes/entry name table at FF95. Print ($FF6D-$FF7F): the looked-up entry's two characters are copied into a 2-character scratch buffer at $FD97-$FD9B alongside the caller's screen address (DE), with bit 7 forced on the second (the string terminator consumed by print_character's own BIT 7 test -- see FF95: usually a space, but a real second letter for the spelled-out SYMBOL SHIFT/SPACE/ENTER/CAPS SHIFT codes), then print_character prints it. Column advance ($FF82-$FF94): restores the caller's screen address and steps it on by $20 (one label column); on overflow (E wraps past $FF) also bumps D by 8 to drop down a pixel row. The same step is applied unconditionally once more when the caller's remaining loop count B is exactly 4 (FF87-$FF8A) -- the extra step that wraps from the first row of 4 control labels to the second row of 4. Used by the routine at redefine_keys_screen.
read_new_key_definition	FF2C	PUSH DE
	FF2D	PUSH BC
read_new_key_definition_0	FF2E	CALL run_title_tune
	FF31	CALL scan_keyboard_matrix
	FF34	JR NZ,read_new_key_definition_0
	FF36	INC D
	FF37	JR Z,read_new_key_definition_0
	FF39	DEC D
	FF3A	LD A,D
	FF3B	POP BC
	FF3C	PUSH BC
	FF3D	LD HL,$FFF7
	FF40	LD B,C
	FF41	DEC B
	FF42	JR Z,read_new_key_definition_2
read_new_key_definition_1	FF44	CP (HL)
	FF45	JR Z,read_new_key_definition_0
	FF47	INC HL
	FF48	DJNZ read_new_key_definition_1
read_new_key_definition_2	FF4A	POP BC
	FF4B	PUSH BC
	FF4C	LD HL,$FFF6
	FF4F	LD B,$00
	FF51	ADD HL,BC
	FF52	LD (HL),A
	FF53	LD HL,$FF95
	FF56	LD D,$00
	FF58	LD B,A
	FF59	AND $07
	FF5B	LD C,A
	FF5C	ADD A,A
	FF5D	ADD A,A
	FF5E	ADD A,C
	FF5F	SRL B
	FF61	SRL B
	FF63	SRL B
	FF65	ADD A,B
	FF66	ADD A,A
	FF67	LD E,A
	FF68	ADD HL,DE
	FF69	POP BC
	FF6A	POP DE
	FF6B	PUSH BC
	FF6C	PUSH DE
	FF6D	LD ($FD98),DE
	FF71	LD A,(HL)
	FF72	LD ($FD9A),A
	FF75	INC HL
	FF76	LD A,(HL)
	FF77	SET 7,A
	FF79	LD ($FD9B),A
	FF7C	LD HL,$FD97
	FF7F	CALL print_character
	FF82	POP DE
	FF83	CALL advance_key_label_column
	FF86	POP BC
	FF87	LD A,B
	FF88	CP $04
	FF8A	RET NZ
advance_key_label_column	FF8B	LD A,E
	FF8C	ADD A,$20
	FF8E	LD E,A
	FF8F	RET NC
	FF90	LD A,D
	FF91	ADD A,$08
	FF93	LD D,A
	FF94	RET