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Routines |
| Prev: F603 | Up: Map | Next: F67E |
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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 00 if nothing is pressed.
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Probe port FEFE first (caps/shift row with bit 00 forced).
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| Read_KeyboardControls | F640 | LD BC,$FEFE | Load BC with keyboard port FEFE. | |
| F643 | LD HL,$F67E | Point HL at Table_KeyboardPortMap. | ||
| F646 | IN A,(C) | Read the half-row. | ||
| F648 | SET 0,A | Force bit 00 set (ignore caps-shift alone). | ||
| F64A | AND %00011111 | Keep the five key bits. | ||
| F64C | XOR %00011111 | Invert so pressed keys are set. | ||
| F64E | JR NZ,Read_KeyboardControls_Decode | If any are pressed, decode at Read_KeyboardControls_Decode. | ||
| F650 | LD DE,$0005 | Load DE with 0005, then advance HL onto the next half-row's key codes. | ||
| F653 | ADD HL,DE | |||
| F654 | LD E,$06 | Load E with 06 remaining half-rows. | ||
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Scan the remaining keyboard half-rows for a pressed key.
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| Read_KeyboardControls_HalfRowLoop | F656 | RLC B | Rotate the port select in B left (next half-row). | |
| F658 | IN A,(C) | Read that half-row. | ||
| F65A | AND %00011111 | Keep the five key bits. | ||
| F65C | XOR %00011111 | Invert so pressed keys are set. | ||
| F65E | JR NZ,Read_KeyboardControls_Decode | If any are pressed, decode at Read_KeyboardControls_Decode. | ||
| F660 | INC HL | Advance HL onto the next half-row's key codes. | ||
| F661 | INC HL | |||
| F662 | INC HL | |||
| F663 | INC HL | |||
| F664 | INC HL | |||
| F665 | DEC E | Decrease the half-row counter. | ||
| F666 | JR NZ,Read_KeyboardControls_HalfRowLoop | Loop at Read_KeyboardControls_HalfRowLoop if more half-rows remain. | ||
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Final half-row: force bit 01 set before testing.
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| F668 | RLC B | Rotate onto the last half-row port. | ||
| F66A | IN A,(C) | Read it. | ||
| F66C | SET 1,A | Force bit 01 set. | ||
| F66E | AND %00011111 | Keep / invert the key bits. | ||
| F670 | XOR %00011111 | Invert so pressed keys are set. | ||
| F672 | JR NZ,Read_KeyboardControls_Decode | If any are pressed, decode at Read_KeyboardControls_Decode. | ||
| F674 | RET | Return with A = 00 (no key). | ||
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Shift through the pressed-bit positions to pick the ASCII code at HL.
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| Read_KeyboardControls_Decode | F675 | SRL A | Shift the pressed-bit mask right, then if that key is pressed, take its code at Read_KeyboardControls_Found. | |
| F677 | JR C,Read_KeyboardControls_Found | |||
| F679 | INC HL | Advance HL onto the next key's code. | ||
| F67A | JR Read_KeyboardControls_Decode | Jump to Read_KeyboardControls_Decode to keep decoding. | ||
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Return the ASCII code for the pressed bit position from the port map.
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| Read_KeyboardControls_Found | F67C | LD A,(HL) | Fetch the ASCII key code at HL. | |
| F67D | RET | Return. | ||
| Prev: F603 | Up: Map | Next: F67E |