Routines
Prev: 35713 Up: Map Next: 35835
35731: Get Key
Used by the routine at Input_WaitForAKey.
Reads a newly pressed key. Returns 0 if there isn't one.
GetKey 35731 PUSH HL Save HL, IX and BC and call Pause to pause.
35732 PUSH IX
35734 PUSH BC
35735 CALL Pause
35738 LD (35721),BC Write 0000 to 35721.
35742 LD HL,35723 Point HL at 35723.
35745 LD IX,35713 Point IX at KeyboardRowMasks.
35749 LD BC,65278 Read the keyboard from port 65278.
GetKey_Loop 35752 IN A,(C) Read from the keyboard port.
35754 AND %00011111 Keep the selected bits.
35756 OR (IX+0) OR against what IX is pointing to.
35759 PUSH AF Save the row and complement it.
35760 CPL
35761 AND (HL) Keep the keys that are pressed now but were up in the previous scan at HL. The second CPL leaves the flags alone.
35762 CPL
35763 JR Z,GetKey_StoreTheRow Jump to GetKey_StoreTheRow if no key in this half-row has been newly pressed.
35765 LD (35721),BC Store BC at 35721.
35769 LD (35721),A Store the result at 35721.
GetKey_StoreTheRow 35772 POP AF Store the result, then step HL on.
35773 LD (HL),A
35774 INC HL
35775 INC IX Step IX to the next byte of KeyboardRowMasks.
35777 RLC B Rotate the next bit of B into carry.
35779 JR C,GetKey_Loop Jump back to GetKey_Loop until all eight half-rows have been read.
35781 LD BC,(35721) Bring BC back from 35721.
No newly pressed key was stored.
35785 LD A,B If BC is 0000, return 0 through GetKey_Return.
35786 OR C
35787 JR Z,GetKey_Return
35789 LD A,251 Start the key index at 251 (that is -5).
GetKey_CountTheRows 35791 ADD A,5 Add 5 for each keyboard row passed.
35793 RRC B Shift the next row bit of B into the carry flag.
35795 JR C,GetKey_CountTheRows If there is any carry, jump to GetKey_CountTheRows.
35797 DEC A Step back one so the next loop starts in the same place.
GetKey_CountTheKeys 35798 INC A Count one more key along the row.
35799 RRC C Shift the next key bit of C into the carry flag.
35801 JR C,GetKey_CountTheKeys If there is any carry, jump to GetKey_CountTheKeys.
35803 LD C,A Copy the key code into C.
35804 LD B,0 Start the character count at zero.
35806 LD HL,35835 Point HL at the unshifted keyboard map at KeyboardMapUnshifted.
35809 LD A,254 Read from the keyboard port.
Port Number Bit
0 1 2 3 4
254 SHIFT Z X C V
35811 IN A,(254)
35813 AND %00000001 Keep only bit 0 (SHIFT).
35815 JR Z,GetKey_UseTheShiftedMap If it is zero, jump to GetKey_UseTheShiftedMap.
35817 LD A,127 Read from the keyboard port.
Port Number Bit
0 1 2 3 4
127 SPACE SYMBOL SHIFT M N B
35819 IN A,(254)
35821 AND %00000010 Keep only bit 1 (SYMBOL SHIFT).
35823 JR NZ,GetKey_GetByte If it is not zero, jump to GetKey_GetByte.
GetKey_UseTheShiftedMap 35825 LD HL,35875 Point HL at the shifted keyboard map at KeyboardMapShifted.
GetKey_GetByte 35828 ADD HL,BC Add the key code in BC to the keyboard map pointer.
35829 LD A,(HL) Read the character for this key from the keyboard map.
GetKey_Return 35830 POP BC Restore BC, IX and HL from the stack.
35831 POP IX
35833 POP HL
35834 RET Return.
Prev: 35713 Up: Map Next: 35835