Routines
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8F9F: 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 8F9F LD C,$FF Start with every control bit released.
8FA1 LD A,$E7 Read from the keyboard;
Port Number Bit
0 1 2 3 4
E7 1 / 0 2 / 9 3 / 8 4 / 7 5 / 6
8FA3 OUT ($FD),A
8FA5 IN A,($FE)
8FA7 CPL Flip the bits.
8FA8 AND %00011111 Keep only bits 0-4.
8FAA JR Z,ReadKeyboard_Letters Jump to ReadKeyboard_Letters if no number key is pressed.
8FAC RES 2,C Reset the DOWN bit.
Read the top letter row; any key pressed in it counts as UP.
ReadKeyboard_Letters 8FAE LD A,$DB Read from the keyboard;
Port Number Bit
0 1 2 3 4
DB Q / P W / O E / I R / U T / Y
8FB0 OUT ($FD),A
8FB2 IN A,($FE)
8FB4 CPL Flip the bits.
8FB5 AND %00011111 Keep only bits 0-4.
8FB7 JR Z,ReadKeyboard_HomeRow Jump to ReadKeyboard_HomeRow if no letter in this row is pressed.
8FB9 RES 3,C Reset the UP bit.
Read the home row; any key pressed in it counts as FIRE.
ReadKeyboard_HomeRow 8FBB LD A,$BD Read from the keyboard;
Port Number Bit
0 1 2 3 4
BD A / ENTER S / L D / K F / J G / H
8FBD OUT ($FD),A
8FBF IN A,($FE)
8FC1 CPL Flip the bits.
8FC2 AND %00011111 Keep only bits 0-4.
8FC4 JR Z,ReadKeyboard_ZXCV Jump to ReadKeyboard_ZXCV if no letter in this row is pressed.
8FC6 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 8FC8 LD A,$FE Read from the keyboard;
Port Number Bit
0 1 2 3 4
FE SHIFT Z X C V
8FCA OUT ($FD),A
8FCC IN A,($FE)
8FCE CPL Flip the bits.
8FCF LD B,A Stash the row in B.
8FD0 AND %00010100 Keep only bits 2 and 4.
8FD2 JR Z,ReadKeyboard_TestC Jump to ReadKeyboard_TestC if neither key is pressed.
8FD4 RES 1,C Reset the LEFT bit.
Reset the RIGHT bit if C is pressed.
ReadKeyboard_TestC 8FD6 LD A,B Fetch the stored row.
8FD7 AND %00001000 Keep only bit 3.
8FD9 JR Z,ReadKeyboard_BNM Jump to ReadKeyboard_BNM if "C" is not pressed.
8FDB 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 8FDD LD A,$7F Read from the keyboard;
Port Number Bit
0 1 2 3 4
7F SPACE FULL-STOP M N B
8FDF OUT ($FD),A
8FE1 IN A,($FE)
8FE3 CPL Flip the bits.
8FE4 LD B,A Stash the row in B.
8FE5 AND %00001000 Keep only bit 3.
8FE7 JR Z,ReadKeyboard_TestFullStop Jump to ReadKeyboard_TestFullStop if "N" is not pressed.
8FE9 RES 1,C Reset the LEFT bit.
Reset the RIGHT bit if M or B is pressed.
ReadKeyboard_TestFullStop 8FEB LD A,B Fetch the stored row.
8FEC AND %00010100 Keep only bits 2 and 4.
8FEE JR Z,ReadKeyboard_ReturnControls Jump to ReadKeyboard_ReturnControls if neither key is pressed.
8FF0 RES 0,C Reset the RIGHT bit.
ReadKeyboard_ReturnControls 8FF2 LD A,C A=the collected controls.
8FF3 RET Return.
View the equivalent code in;
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