Routines
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36767: Controls: Keyboard
Read the movement and fire rows into the same bit order as the Kempston joystick.
Output
A Controls
Start with every control bit released, then read 0-9.
ReadKeyboard 36767 LD C,255 Start with every control bit released.
36769 LD A,231 Read from the keyboard;
Port Number Bit
0 1 2 3 4
231 1 / 0 2 / 9 3 / 8 4 / 7 5 / 6
36771 OUT (253),A
36773 IN A,(254)
36775 CPL Flip the bits.
36776 AND %00011111 Keep only bits 0-4.
36778 JR Z,ReadKeyboard_Letters Jump to ReadKeyboard_Letters if no number key is pressed.
36780 RES 2,C Reset the DOWN bit.
Read the top letter row; any key pressed in it counts as UP.
ReadKeyboard_Letters 36782 LD A,219 Read from the keyboard;
Port Number Bit
0 1 2 3 4
219 Q / P W / O E / I R / U T / Y
36784 OUT (253),A
36786 IN A,(254)
36788 CPL Flip the bits.
36789 AND %00011111 Keep only bits 0-4.
36791 JR Z,ReadKeyboard_HomeRow Jump to ReadKeyboard_HomeRow if no letter in this row is pressed.
36793 RES 3,C Reset the UP bit.
Read the home row; any key pressed in it counts as FIRE.
ReadKeyboard_HomeRow 36795 LD A,189 Read from the keyboard;
Port Number Bit
0 1 2 3 4
189 A / ENTER S / L D / K F / J G / H
36797 OUT (253),A
36799 IN A,(254)
36801 CPL Flip the bits.
36802 AND %00011111 Keep only bits 0-4.
36804 JR Z,ReadKeyboard_ZXCV Jump to ReadKeyboard_ZXCV if no letter in this row is pressed.
36806 RES 4,C Reset the FIRE bit.
Read the bottom-left row; X and V count as LEFT and C counts as RIGHT.
ReadKeyboard_ZXCV 36808 LD A,254 Read from the keyboard;
Port Number Bit
0 1 2 3 4
254 SHIFT Z X C V
36810 OUT (253),A
36812 IN A,(254)
36814 CPL Flip the bits.
36815 LD B,A Stash the row in B.
36816 AND %00010100 Keep only bits 2 and 4.
36818 JR Z,ReadKeyboard_TestC Jump to ReadKeyboard_TestC if neither key is pressed.
36820 RES 1,C Reset the LEFT bit.
Reset the RIGHT bit if C is pressed.
ReadKeyboard_TestC 36822 LD A,B Fetch the stored row.
36823 AND %00001000 Keep only bit 3.
36825 JR Z,ReadKeyboard_BNM Jump to ReadKeyboard_BNM if "C" is not pressed.
36827 RES 0,C Reset the RIGHT bit.
Read the bottom-right row; N counts as LEFT and M or B counts as RIGHT.
ReadKeyboard_BNM 36829 LD A,127 Read from the keyboard;
Port Number Bit
0 1 2 3 4
127 SPACE FULL-STOP M N B
36831 OUT (253),A
36833 IN A,(254)
36835 CPL Flip the bits.
36836 LD B,A Stash the row in B.
36837 AND %00001000 Keep only bit 3.
36839 JR Z,ReadKeyboard_TestFullStop Jump to ReadKeyboard_TestFullStop if "N" is not pressed.
36841 RES 1,C Reset the LEFT bit.
Reset the RIGHT bit if M or B is pressed.
ReadKeyboard_TestFullStop 36843 LD A,B Fetch the stored row.
36844 AND %00010100 Keep only bits 2 and 4.
36846 JR Z,ReadKeyboard_ReturnControls Jump to ReadKeyboard_ReturnControls if neither key is pressed.
36848 RES 0,C Reset the RIGHT bit.
ReadKeyboard_ReturnControls 36850 LD A,C A=the collected controls.
36851 RET Return.
View the equivalent code in;
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