Routines
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618C: Input: Left/ Right
Used by the routine at 6E32.
Check if this should be read from the Kempston joystick instead?
ReadInputLR 618C LD A,($5E3E) If GameOptions indicates the control method is via the Kempston joystick then jump to ReadKempstonJoystick.
618F BIT 1,A
6191 JR NZ,ReadKempstonJoystick
Check for "Left" and "Right" button inputs for port FE.
6193 LD A,$FE Read from the keyboard;
Port Number Bit
0 1 2 3 4
$FE SHIFT Z X C V
6195 OUT ($FD),A
6197 IN A,($FE)
6199 AND %00011110 Strip out the SHIFT key.
619B CP $1E If none of these keys have been pressed, jump to ReadInputLR_7F.
619D JR Z,ReadInputLR_7F
619F AND %00010100 Keep only bits 2 ("X") and 4 ("V").
61A1 CP $14 If neither key is pressed jump to Input_Left.
61A3 JR Z,Input_Left
61A5 JR Input_Right Jump to Input_Right.
Check for "Left" and "Right" button input for port 7F.
ReadInputLR_7F 61A7 LD A,$7F Read from the keyboard;
Port Number Bit
0 1 2 3 4
$7F SPACE FULL-STOP M N B
61A9 OUT ($FD),A
61AB IN A,($FE)
61AD AND %00011110 Strip out the SPACE key.
61AF CP $1E If none of these keys have been pressed, jump to Input_None.
61B1 JR Z,Input_None
61B3 AND %00010100 Keep only bits 2 ("M") and 4 ("B").
61B5 CP $14 If neither key is pressed jump to Input_Right.
61B7 JR Z,Input_Right
Return "Left" button pressed.
Input_Left 61B9 LD A,$FD A=11111101.
61BB RET Return.
Return "Right" button pressed.
Input_Right 61BC LD A,$FE A=11111110.
61BE RET Return.
Return "no input".
Input_None 61BF LD A,$FF A=11111111.
61C1 RET Return.
View the equivalent code in;
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