Avalon: Routine at 80FD

80FD: Menu 1: Check if ENTER pressed to confirm player controls

This follows the previous routine at 80C1, or a jump from 80BF, after the player has made a choice of controls on the first game menu.
Pressing ENTER confirms the controls choice, and launches the second game menu. Once the choice of controls has been made, the player can't change it without reloading the game.
80FD	LD BC,$BFFE	Keyboard port for keys H, J, K, L, Enter
8100	IN A,(C)	Read the port input
8102	OR %11111110	We're only interested in bit 0, but set bits 1-7 for the CP in the next instruction
8104	CP %11111111	Check if ENTER is being pressed (bit 0 will be reset if so)
8106	JR Z,$80A1	If ENTER isn't being pressed, return to checking keys for other menu options
ENTER has been pressed, player controls choice confirmed.
8108	CALL $815B	Clear the screen (pixels)
ENTER is still being pressed - wait until the key has been released
810B	LD BC,$BFFE	Keyboard port for keys H, J, K, L, Enter
810E	IN A,(C)	Read the port input
8110	OR %11111110	We're only interested in bit 0, but set bits 1-7 for the CP in the next instruction
8112	CP %11111111	Check if ENTER is still being pressed
8114	JR NZ,$810B	If so, keep checking until it's been released
ENTER has now been released
8116	LD A,$0F	Set the screen attributes to INK 7, PAPER 1
8118	CALL $816A	...and reset screen colours with this colour (mainly to clear the flashing colour marking the player's control selection)