| Routines

F7CD: Open a door

Used by the routine at F2A8. Updates the play area graphics and screen refresh buffer (SRB) for a door so that it appears open.
Input
HL | Address of the door status flags (see 7FF0)
F7CD | PUSH HL | Save the address of the door status flags
F7CE | LD A,L | A=0xF0-0xF9
F7CF | SUB $46 | Point HL at the door knock status flags for the door (see 7FAA)
F7D1 | LD L,A
F7D2 | LD A,(HL) | Reset the door knock status flags
F7D3 | AND $3F
F7D5 | LD (HL),A
F7D6 | POP HL | Restore the address of the door status flags to HL
F7D7 | JP $F100 | Update the play area graphics and the SRB for the door