The keypress flag in bit 0 is initialised by the routine at 87CA; bits 0 and 1 are checked and updated by the routine at 8B07.

Bit(s)	Meaning
0	Keypress flag (set=H-ENTER being pressed, reset=no key pressed)
1	In-game music flag (set=music off, reset=music on)
2-7	Unused