Routines
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24972: Input: Left/ Right
Used by the routine at HandlerSteering.
Reads the steering controls. From the keyboard the car steers left with Z, C, M or B, and steers right with X, V, N or FULL-STOP.
Output
A 253 if left is pressed, 254 if right is pressed, else 255
Check if this should be read from the Kempston joystick instead?
ReadInputLR 24972 LD A,(24126) If GameOptions indicates the control method is via the Kempston joystick then jump to ReadKempstonJoystick.
24975 BIT 1,A
24977 JR NZ,ReadKempstonJoystick
Check for "Left" and "Right" button inputs for port 254.
24979 LD A,254 Read from the keyboard;
Port Number Bit
0 1 2 3 4
254 SHIFT Z X C V
24981 OUT (253),A
24983 IN A,(254)
24985 AND %00011110 Keep only bits 1-4 (stripping out the SHIFT key).
24987 CP 30 If none of these keys have been pressed, jump to ReadInputLR_7F.
24989 JR Z,ReadInputLR_7F
24991 AND %00010100 Keep only bits 2 ("X") and 4 ("V").
24993 CP 20 If neither key is pressed ("Z" or "C" is) jump to Input_Left.
24995 JR Z,Input_Left
24997 JR Input_Right Else "X" or "V" was pressed, so jump to Input_Right.
Check for "Left" and "Right" button input for port 127.
ReadInputLR_7F 24999 LD A,127 Read from the keyboard;
Port Number Bit
0 1 2 3 4
127 SPACE FULL-STOP M N B
25001 OUT (253),A
25003 IN A,(254)
25005 AND %00011110 Keep only bits 1-4 (stripping out the SPACE key).
25007 CP 30 If none of these keys have been pressed, jump to Input_None.
25009 JR Z,Input_None
25011 AND %00010100 Keep only bits 2 ("M") and 4 ("B").
25013 CP 20 If neither key is pressed ("N" or "FULL-STOP" is) jump to Input_Right.
25015 JR Z,Input_Right
Return "Left" button pressed.
Input_Left 25017 LD A,253 A=11111101.
25019 RET Return.
Return "Right" button pressed.
Input_Right 25020 LD A,254 A=11111110.
25022 RET Return.
This entry point is used by the routines at ReadInputBrake and ReadInputAccelerate.
Return "no input".
Input_None 25023 LD A,255 A=11111111.
25025 RET Return.
View the equivalent code in;
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