Routines
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F271: Keyboard input routine
Input
C On return holds the appropriate action : 0 - jump right, 1 - move right, 2 - jump left, 3 - move left, 4 - jump, 5 - no action
F271 LD HL,$F26E Point HL at the key for left.
F274 LD E,$00 Initialize E to no keys pressed.
F276 LD D,$03 Number of keys to check.
F278 LD A,(HL) Get the key to press.
F279 CALL $F32A See if it was pressed.
F27C CCF Invert the carry flag, then rotate E, putting the flag in as bit 0. This allows the various key presses to be built up as the keys are checked.
F27D RL E
F27F INC HL Move to the next key.
F280 DEC D Loop until all keys checked.
F281 JR NZ,$F278
All keys have been scanned, now check the values.
F283 LD A,E Get the matrix of keys pressed.
F284 AND $06 Only consider bits 1 - 2.
F286 CP $06 Is the value 6?
F288 JR NZ,$F28E Jump forward if not.
F28A LD A,E Clear all bits except 1.
F28B AND $01
F28D LD E,A
Now decide what action to take.
F28E LD C,$05 Default to value 5 (no action).
F290 LD A,E Get the matrix of keys.
F291 AND A Return if it is zero (nothing pressed).
F292 RET Z
F293 DEC C Select option 4 (jump).
F294 CP $01 Is only the jump bit set?
F296 RET Z Return if it is.
F297 DEC C Select option 3 (left).
F298 CP $04 Is left pressed but not jump?
F29A RET Z Return if it is.
F29B DEC C Select option 2 (jump + left).
F29C CP $05 Are left and jump pressed?
F29E RET Z Return if they are.
F29F DEC C Selecti option 1 (right).
F2A0 CP $02 Is right pressed but not jump?
F2A2 RET Z Return if is.
F2A3 DEC C Only option left is right and jump pressed, select option 0 (jump right) and return.
F2A4 RET
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