Routines
Prev: 62979 Up: Map Next: 63102
63040: Read Keyboard Controls
Used by the routines at MainMenu_ChooseLearnerOrSuper, MainMenu_SelectOptions and Read_PlayerControls.
Scan the keyboard half-rows via Table_KeyboardPortMap and return the matching ASCII key code in A, or 0 if nothing is pressed.
Probe port 65278 first (caps/shift row with bit 0 forced).
Read_KeyboardControls 63040 LD BC,65278 Load BC with keyboard port 65278.
63043 LD HL,63102 Point HL at Table_KeyboardPortMap.
63046 IN A,(C) Read the half-row.
63048 SET 0,A Force bit 0 set (ignore caps-shift alone).
63050 AND %00011111 Keep the five key bits.
63052 XOR %00011111 Invert so pressed keys are set.
63054 JR NZ,Read_KeyboardControls_Decode If any are pressed, decode at Read_KeyboardControls_Decode.
63056 LD DE,5 Load DE with 0005, then advance HL onto the next half-row's key codes.
63059 ADD HL,DE
63060 LD E,6 Load E with 6 remaining half-rows.
Scan the remaining keyboard half-rows for a pressed key.
Read_KeyboardControls_HalfRowLoop 63062 RLC B Rotate the port select in B left (next half-row).
63064 IN A,(C) Read that half-row.
63066 AND %00011111 Keep the five key bits.
63068 XOR %00011111 Invert so pressed keys are set.
63070 JR NZ,Read_KeyboardControls_Decode If any are pressed, decode at Read_KeyboardControls_Decode.
63072 INC HL Advance HL onto the next half-row's key codes.
63073 INC HL
63074 INC HL
63075 INC HL
63076 INC HL
63077 DEC E Decrease the half-row counter.
63078 JR NZ,Read_KeyboardControls_HalfRowLoop Loop at Read_KeyboardControls_HalfRowLoop if more half-rows remain.
Final half-row: force bit 1 set before testing.
63080 RLC B Rotate onto the last half-row port.
63082 IN A,(C) Read it.
63084 SET 1,A Force bit 1 set.
63086 AND %00011111 Keep / invert the key bits.
63088 XOR %00011111 Invert so pressed keys are set.
63090 JR NZ,Read_KeyboardControls_Decode If any are pressed, decode at Read_KeyboardControls_Decode.
63092 RET Return with A = 0 (no key).
Shift through the pressed-bit positions to pick the ASCII code at HL.
Read_KeyboardControls_Decode 63093 SRL A Shift the pressed-bit mask right, then if that key is pressed, take its code at Read_KeyboardControls_Found.
63095 JR C,Read_KeyboardControls_Found
63097 INC HL Advance HL onto the next key's code.
63098 JR Read_KeyboardControls_Decode Jump to Read_KeyboardControls_Decode to keep decoding.
Return the ASCII code for the pressed bit position from the port map.
Read_KeyboardControls_Found 63100 LD A,(HL) Fetch the ASCII key code at HL.
63101 RET Return.
Prev: 62979 Up: Map Next: 63102