Volex TTX2000 S Issue 1.2: Routine at 0A52

0A52: code_set_at: Display character.

Used by the routines at decode_row, normal_code, double_code, contiguous_code, separated_code, black_background_code, new_background_code and hold_mosaics_code.
code_set_at	0A52	LD A,(hold_mosaics_flag)	If hold_mosaics_flag is clear then jump to display_space.
	0A55	AND A
	0A56	JR Z,display_space
This entry point is used by the routine at release_mosaics_code.
hold_mosaics	0A58	LD A,(mosaics_flag)	If mosaics_flag is clear then jump to display_space.
	0A5B	AND A
	0A5C	JR Z,display_space
	0A5E	LD A,(hold_mosaic_character)	Else copy hold_mosaic_character to character_code.
	0A61	LD (character_code),A	Else copy hold_mosaic_character to character_code.
	0A64	JR apply_colours	Skip forward to apply_colours.
display_space	0A66	LD A,$20	Set character_code to $20 (space character).
	0A68	LD (character_code),A	Set character_code to $20 (space character).
This entry point is used by the routines at decode_row, separated_code and hold_mosaics_code.
apply_colours	0A6B	CALL set_attrs
This entry point is used by the routines at alpha_colour_code, mosaics_colour_code and conceal_code.
code_set_after	0A6E	CALL print_character
	0A71	LD A,(column_offset)	If column_offset is not 0 increment char_addr.
	0A74	AND A
	0A75	JR Z,char_addr_set
	0A77	LD HL,(char_addr)
	0A7A	INC HL
	0A7B	LD (char_addr),HL
char_addr_set	0A7E	LD HL,(character_pointer)	Increment character_pointer.
	0A81	INC HL
	0A82	LD (character_pointer),HL
	0A85	POP AF	Pop column counter off the stack and decrement it. Loop back to decode_character for 40 columns.
	0A86	DEC A
	0A87	JP NZ,decode_character
	0A8A	LD A,(row_number)	Return if row_number is greater than or equal to 23.
	0A8D	CP $17
	0A8F	RET NC
	0A90	LD A,(row_has_double_flag)	Return if row_has_double_flag is clear.
	0A93	AND A
	0A94	RET Z
set_bottom_row_attrs	0A95	LD HL,(current_attr_address)	Else set HL to current_attr_address - 29 (second display attr byte of this row) and DE to current_attr_address + 3 (second display attr byte of next row).
	0A98	LD BC,$001D
	0A9B	OR A
	0A9C	SBC HL,BC
	0A9E	EX DE,HL
	0A9F	LD HL,(current_attr_address)
	0AA2	INC HL
	0AA3	INC HL
	0AA4	INC HL
	0AA5	EX DE,HL
	0AA6	LD B,$1E	Set B to 30 as loop counter.
copy_attrs_down_loop.	0AA8	PUSH BC	Preserve loop counter.
	0AA9	LD A,(HL)	Copy paper colour bits from attr byte into corresponding attr byte in next row.
	0AAA	AND $38
	0AAC	LD B,A
	0AAD	LD A,(DE)
	0AAE	AND $C7
	0AB0	OR B
	0AB1	LD (DE),A
	0AB2	POP BC	Restore loop counter and increment addresses.
	0AB3	INC HL
	0AB4	INC DE
	0AB5	DJNZ copy_attrs_down_loop.	Loop through 30 attr bytes and return.
	0AB7	RET	Loop through 30 attr bytes and return.