Routines
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7C75: Collect the bit mask and game status buffer address for an event identifier
Used by the routine at 7C8F, and also by the unused routines at 7C95 and 7CA1. The event identifier in A (0x00, 0x07-0x0C), taken modulo 8, corresponds to a bit in one of the bytes at 7F80 (A<=7) or 7F81 (A>=8). On exit, HL points to the appropriate byte and A holds the bit mask (single bit set), as follows:
Entry Exit Event
0x00 0x01 End of lesson
0x07 0x80 Time to sit down for assembly
0x08 0x01 Teacher has arrived at the top-floor room in the girls' skool
0x09 0x02 Teacher has arrived at the middle-floor room in the girls' skool
0x0A 0x04 Teacher has arrived at the Blue Room
0x0B 0x08 Teacher has arrived at the Yellow Room
0x0C 0x10 Teacher has arrived at the Science Lab
Input
A Event ID from a command list
7C75 AND A Set the carry flag if the event identifier is odd
7C76 RRA
7C77 LD E,A Copy bits 1-3 of the event ID into bits 0-2 of E
7C78 LD A,$00 A=0x01 if the event ID is an even number, 0x02 if it's an odd number
7C7A ADC A,A
7C7B INC A
7C7C RR E Now bits 2 and 3 of the event ID are in bits 0 and 1 of E
7C7E JR NC,$7C82 Jump if the event ID is 0x00, 0x08, 0x09 or 0x0C (bit 1 reset)
7C80 ADD A,A A=0x04 (event ID = 0x0A) or 8 (event ID = 0x07 or 0x0B)
7C81 ADD A,A
7C82 SCF
7C83 RR E E=0x80 (event ID <= 0x07) or 0x81
7C85 JR NC,$7C8B Jump if the event ID is 0x00, 0x08, 0x09, 0x0A or 0x0B (bit 2 reset)
7C87 ADD A,A A=0x10 (event ID = 0x0C) or 0x80 (event ID = 0x07)
7C88 ADD A,A
7C89 ADD A,A
7C8A ADD A,A
7C8B LD D,$7F HL=7F80 or 7F81
7C8D EX DE,HL
7C8E RET
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