Routines
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F71E: Read Control Sinclair
Control mode 03: reads keyboard ports F7FE and EFFE four times, extracting one direction or fire bit from each read.
Read_Control_Sinclair F71E LD BC,$F7FE Read from the keyboard;
Port Number Bit
0 1 2 3 4
F7 1 2 3 4 5
F721 IN A,(C)
F723 OR %11101111 Isolate bit 4 from the first row.
F725 LD E,A Save the masked result.
F726 LD B,$EF Read from the keyboard;
Port Number Bit
0 1 2 3 4
EF 0 9 8 7 6
F728 IN A,(C)
F72A OR %11111110 Isolate bit 0 from the second row.
F72C AND E Merge with and save the accumulated result.
F72D LD E,A
F72E IN A,(C) Read from the keyboard;
Port Number Bit
0 1 2 3 4
EF 0 9 8 7 6
F730 OR %11100111 Isolate bits 3 and 4 from this read.
F732 RRCA Shift the isolated bits into position.
F733 RRCA
F734 AND E Merge with and save the accumulated result.
F735 LD E,A
F736 IN A,(C) Read from the keyboard;
Port Number Bit
0 1 2 3 4
EF 0 9 8 7 6
F738 OR %11111011 Isolate bit 2 from this read.
F73A RLCA Shift into position and merge with the accumulated result.
F73B AND E
F73C RET Return to Read_Control_Input_Return.
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