The Hobbit: Routine at 946D

946D: LOCK WITH, once the right key is known

Used by the routine at ROCK_DOOR_KEY. Not if it is locked or open, and not with a broken key ("the ... is broken."). The same code unlocks, from DO_UNLOCK, by writing the last byte of the SET 0 or RES 0 at LOCK_BIT_OP.
DO_LOCK	946D	CALL LOCK_STATE	Locked or open already: say which
	9470	JP NZ,SAY_STATE	Locked or open already: say which
	9473	LD A,$C6	SET 0: lock it
This entry point is used by the routine at DO_UNLOCK.
TURN_KEY	9475	LD ($948B),A	}
	9478	LD IY,(INSTRUMENT_RECORD)	A broken key will not turn
	947C	BIT 3,(IY+$07)
	9480	LD A,$83
	9482	JP NZ,SAY_STATE_OF
	9485	CALL FOR_REAL	The test ends here
LOCK_BIT_OP	9488	SET 0,(IX+$07)	Bit 0: locked, or not
	948C	RET