| Routines

F6AA: Deal with ERIC when he's writing on a blackboard

Called from the main loop at 6767 when bit 5 of ERIC's status flags at 7FFB is set (by the routine at F650).
Input
A | ASCII code of the last keypress
HL | 7FFB (ERIC's status flags)
F6AA | CP $0D | Was ENTER pressed?
F6AC | JR Z,$F6D4 | Jump if so
F6AE | LD B,A | Store the keypress code in B
F6AF | LD H,$AC | 0xAC=ERIC
F6B1 | CALL $7128 | C=0xAB (Reading Room blackboard), 0xB1 (White Room blackboard) or 0xB7 (Exam Room blackboard)
F6B4 | SUB $B3
F6B6 | LD C,A
F6B7 | ADD A,A
F6B8 | ADD A,C
F6B9 | LD C,A
F6BA | LD L,A | Point HL at byte 3 of the relevant blackboard contents buffer)
F6BB | LD H,$7F
F6BD | BIT 7,(HL) | Jump if 4 or more characters have been written so far, or the board was dirty before ERIC started writing
F6BF | JR Z,$F6CA
F6C1 | SUB $04 | Point HL at the byte preceding the first byte of the relevant blackboard contents buffer
F6C3 | LD L,A
F6C4 | INC L | Find the next 'open' slot (which will have bit 7 set) in the blackboard contents buffer
F6C5 | BIT 7,(HL)
F6C7 | JR Z,$F6C4
F6C9 | LD (HL),B | Store the keypress code in the blackboard contents buffer
F6CA | INC C | Restore the keypress code to A; set BC=7FAC (Reading Room blackboard), 7FB2 (White Room blackboard), or 7FB8 (Exam Room blackboard) (which holds the pixel coordinates at which ERIC should write)
F6CB | LD A,B
F6CC | LD B,$7F
F6CE | CALL $715F | Write a single character on the blackboard
F6D1 | JP $F693 | Move ERIC's arm
ERIC has finished writing on the board (ENTER was pressed).
F6D4 | RES 5,(HL) | Reset bit 5 of ERIC's status flags at 7FFB to indicate that ERIC has finished writing on the board
F6D6 | RET | Return to the main loop