Routines
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48632: Read Controls
Used by the routine at HandlePlayerLegs.
Reads the keyboard or the joystick, according to the control method that was chosen in the menu, and writes what is wanted to ControlsPressed as a set of bits:
Bit Meaning
0 Turn left
1 Turn right
2 Walk forward
3 Jump
4 Pick up or drop an object
6 Fire
With the keyboard, any of several keys do each action. With a joystick, up walks forward, down jumps and fire fires, and a long list of the keys of the keyboard picks up or drops an object.
CAPS SHIFT and SPACE are left alone by this routine, as they pause the game (see PauseGame).
Output
C The controls, also written to ControlsPressed
Find the control method: 0 is the keyboard, 1 is a Kempston joystick, 2 is a cursor joystick and 3 is an Interface II joystick.
ReadControls 48632 LD A,(42761) Fetch the control method.
48635 RRCA Shift the method down to bits 0 and 1...
48636 AND %00000011 ...and keep only those bits.
48638 JP Z,ReadControls_Keyboard Jump to ReadControls_Keyboard to read the keyboard if the method is 0.
48641 DEC A Jump to ReadControls_Kempston to read a Kempston joystick if the method is 1.
48642 JR Z,ReadControls_Kempston
48644 DEC A Jump to ReadControls_Cursor to read a cursor joystick if the method is 2.
48645 JR Z,ReadControls_Cursor
Read an Interface II joystick, which can be either of the two ports of the interface: they are the keys 1 to 5 (left, right, down, up, fire) and the keys 6, 7, 8, 9 and 0 (left, right, down, up, fire).
48647 LD A,247 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
247 1 2 3 4 5
48649 CALL ReadKeyboardPort
48652 PUSH BC Stash BC on the stack.
48653 LD B,5 Set a counter in B of five keys.
ReadControls_Reverse 48655 RRA Reverse the order of the five bits, so that they line up with the keys of the second port.
48656 RL C
48658 DJNZ ReadControls_Reverse
48660 LD A,C Move the reversed keys to A.
48661 POP BC Restore BC from the stack.
48662 LD C,A Move the reversed keys to C.
48663 LD A,239 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
239 0 9 8 7 6
48665 CALL ReadKeyboardPort
48668 OR C Add the keys from the first port to those of the second.
48669 LD C,0 Start with no controls.
48671 BIT 0,A Set the bit for fire if fire is pressed.
48673 JR Z,ReadControls_Interface2Up
48675 SET 6,C
ReadControls_Interface2Up 48677 BIT 1,A Set the bit for walking forward if up is pressed.
48679 JR Z,ReadControls_Interface2Down
48681 SET 2,C
ReadControls_Interface2Down 48683 BIT 2,A Set the bit for jumping if down is pressed.
48685 JR Z,ReadControls_Interface2Right
48687 SET 3,C
ReadControls_Interface2Right 48689 BIT 3,A Set the bit for turning right if right is pressed.
48691 JR Z,ReadControls_Interface2Left
48693 SET 1,C
ReadControls_Interface2Left 48695 BIT 4,A Set the bit for turning left if left is pressed.
48697 JR Z,ReadControls_Interface2Keys
48699 SET 0,C
ReadControls_Interface2Keys 48701 JP ReadControls_Keys Jump to ReadControls_Keys to check the keys for picking up and dropping.
Read a Kempston joystick, whose bits are right, left, down, up and fire.
ReadControls_Kempston 48704 IN A,(31) Read the joystick.
48706 LD C,0 Start with no controls.
48708 BIT 0,A Set the bit for turning right if right is pressed.
48710 JR Z,ReadControls_KempstonLeft
48712 SET 1,C
ReadControls_KempstonLeft 48714 BIT 1,A Set the bit for turning left if left is pressed.
48716 JR Z,ReadControls_KempstonDown
48718 SET 0,C
ReadControls_KempstonDown 48720 BIT 2,A Set the bit for jumping if down is pressed.
48722 JR Z,ReadControls_KempstonUp
48724 SET 3,C
ReadControls_KempstonUp 48726 BIT 3,A Set the bit for walking forward if up is pressed.
48728 JR Z,ReadControls_KempstonFire
48730 SET 2,C
ReadControls_KempstonFire 48732 BIT 4,A Set the bit for fire if fire is pressed.
48734 JR Z,ReadControls_KempstonKeys
48736 SET 6,C
ReadControls_KempstonKeys 48738 JP ReadControls_Keys Jump to ReadControls_Keys to check the keys for picking up and dropping.
Read a cursor joystick, which is the keys 5 (left), 6 (down), 7 (up), 8 (right) and 0 (fire).
ReadControls_Cursor 48741 LD C,0 Start with no controls.
48743 LD A,247 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
247 1 2 3 4 5
48745 CALL ReadKeyboardPort
48748 BIT 4,A Set the bit for turning left if the key 5 is pressed.
48750 JR Z,ReadControls_CursorFire
48752 SET 0,C
ReadControls_CursorFire 48754 LD A,239 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
239 0 9 8 7 6
48756 CALL ReadKeyboardPort
48759 BIT 0,A Set the bit for fire if the key 0 is pressed.
48761 JR Z,ReadControls_CursorUp
48763 SET 6,C
ReadControls_CursorUp 48765 BIT 3,A Set the bit for walking forward if the key 7 is pressed.
48767 JR Z,ReadControls_CursorRight
48769 SET 2,C
ReadControls_CursorRight 48771 BIT 2,A Set the bit for turning right if the key 8 is pressed.
48773 JR Z,ReadControls_CursorDown
48775 SET 1,C
ReadControls_CursorDown 48777 BIT 4,A Set the bit for jumping if the key 6 is pressed.
48779 JR Z,ReadControls_Keys
48781 SET 3,C
48783 JR ReadControls_Keys Jump to ReadControls_Keys to check the keys for picking up and dropping.
Read the keyboard. The keys that turn left are Z, C, M and B and those that turn right are X, V, SYMBOL SHIFT and N.
ReadControls_Keyboard 48785 LD A,254 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
254 CAPS SHIFT Z X C V
48787 CALL ReadKeyboardPort
48790 RRCA Shift the keys down by one, which drops CAPS SHIFT and leaves Z and C for turning left, and X and V for turning right.
48791 LD C,A Stash them in C.
48792 AND %00000011 Keep the keys Z and X.
48794 SRL C Shift the keys C and V down to the same place.
48796 SRL C
48798 OR C Combine them with the keys Z and X.
48799 AND %00000011 Keep the two bits for turning left and turning right.
48801 LD C,A Set the turning bits of the controls.
48802 LD A,127 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
127 SPACE SYMBOL SHIFT M N B
48804 CALL ReadKeyboardPort
48807 BIT 1,A Set the bit for turning right if SYMBOL SHIFT is pressed.
48809 JR Z,ReadControls_KeyboardM
48811 SET 1,C
ReadControls_KeyboardM 48813 BIT 2,A Set the bit for turning left if M is pressed.
48815 JR Z,ReadControls_KeyboardN
48817 SET 0,C
ReadControls_KeyboardN 48819 BIT 3,A Set the bit for turning right if N is pressed.
48821 JR Z,ReadControls_KeyboardB
48823 SET 1,C
ReadControls_KeyboardB 48825 BIT 4,A Set the bit for turning left if B is pressed.
48827 JR Z,ReadControls_KeyboardWalk
48829 SET 0,C
ReadControls_KeyboardWalk 48831 LD A,189 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
189 A or ENTER S or L D or K F or J G or H
48833 CALL ReadKeyboardPort
48836 JR Z,ReadControls_KeyboardJumpKeys Set the bit for walking forward if any of those keys is pressed.
48838 SET 2,C
ReadControls_KeyboardJumpKeys 48840 LD A,223 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
223 P O I U Y
48842 CALL ReadKeyboardPort
48845 LD B,A Stash the keys in B, which is not used.
48846 AND %00001010 Keep the keys O and U.
48848 JR NZ,ReadControls_KeyboardJump Jump to ReadControls_KeyboardJump if either of them is pressed.
48850 LD A,251 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
251 Q W E R T
48852 CALL ReadKeyboardPort
48855 LD E,A Stash the keys in E, which is not used.
48856 AND %00010101 Keep the keys Q, E and T.
48858 JR Z,ReadControls_KeyboardAction Jump to ReadControls_KeyboardAction if none of them is pressed.
ReadControls_KeyboardJump 48860 SET 3,C Set the bit for jumping, as one of the keys Q, E, T, O and U is pressed.
ReadControls_KeyboardAction 48862 LD A,231 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
231 1 or 0 2 or 9 3 or 8 4 or 7 5 or 6
48864 CALL ReadKeyboardPort
48867 JR Z,ReadControls_KeyboardFire Jump to ReadControls_KeyboardFire if none of the number keys is pressed.
48869 SET 4,C Set the bit for picking up and dropping, as a number key is pressed.
ReadControls_KeyboardFire 48871 LD A,223 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
223 P O I U Y
48873 CALL ReadKeyboardPort
48876 AND %00010101 Keep the keys P, I and Y.
48878 JR NZ,ReadControls_KeyboardSetFire Jump to ReadControls_KeyboardSetFire if one of them is pressed.
48880 LD A,251 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
251 Q W E R T
48882 CALL ReadKeyboardPort
48885 AND %00001010 Keep the keys W and R.
48887 JR Z,ReadControls_Done Jump to ReadControls_Done if neither is pressed.
ReadControls_KeyboardSetFire 48889 SET 6,C Set the bit for fire, as one of the keys P, I, Y, W and R is pressed.
48891 JR ReadControls_Done Jump to ReadControls_Done to finish.
With a joystick, the keys of the keyboard other than CAPS SHIFT and SPACE are used to pick up and drop an object.
ReadControls_Keys 48893 LD A,126 Read from the keyboard, with a call to ReadKeyboardPort that returns the pressed keys as set bits;
Port Number Bit
0 1 2 3 4
126 CAPS SHIFT or SPACE Z or SYMBOL SHIFT X or M C or N V or B
48895 CALL ReadKeyboardPort
48898 AND %00011110 Keep the keys other than CAPS SHIFT and SPACE.
48900 JR Z,ReadControls_Done Jump to ReadControls_Done if none of them is pressed.
48902 SET 4,C Set the bit for picking up and dropping.
ReadControls_Done 48904 LD A,C Copy the controls to A.
48905 LD (42807),A Write them to ControlsPressed.
48908 RET Return.
View the equivalent code in;
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