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Routines |
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| 47788 | EXX | Swap registers | ||||||
| 47789 | LD BC,65278 | Load B and C with 254 | ||||||
| 47792 | LD HL,47853 | Point HL at list of return values | ||||||
| 47795 | IN A,(C) | Read from port 254 into A (i.e. read keyboard) [IN 65278 reads the half row CAPS SHIFT to V] | ||||||
| 47797 | SET 0,A | Set bit 0 of A (i.e. clear pressing of CAPS SHIFT) | ||||||
| 47799 | AND 31 | Strip out all but the five bits representing key presses | ||||||
| 47801 | XOR 31 | Invert all of the lowest five bits | ||||||
| 47803 | JR NZ,47843 | If this value is non-zero, then a key has been pressed, so skip ahead to 47843 | ||||||
| 47805 | LD DE,5 | Advance HL by five characters in list of return values string... | ||||||
| 47808 | ADD HL,DE | ... | ||||||
| 47809 | LD E,6 | Load E with 6 as there are 6 keyboard half-rows to test (loop counter) | ||||||
| 47811 | RLC B | With each loop, change BC from 65278 -> 65022 -> 64510 -> 63486 -> 61438 -> 57342 -> 49150 | ||||||
| 47813 | IN A,(C) | Read from port 254 into A (i.e. read keyboard) | ||||||
| 47815 | AND 31 | Strip out all but the five bits representing key presses | ||||||
| 47817 | XOR 31 | Invert all of the lowest five bits | ||||||
| 47819 | JR NZ,47843 | If this value is non-zero, then a key has been pressed, so skip ahead to 47843 | ||||||
| 47821 | INC HL | Advance HL by five characters in list of return values string... | ||||||
| 47822 | INC HL | ... | ||||||
| 47823 | INC HL | ... | ||||||
| 47824 | INC HL | ... | ||||||
| 47825 | INC HL | ... | ||||||
| 47826 | DEC E | Decrease number of remaining keyboard half-rows to check | ||||||
| 47827 | JR NZ,47811 | If there are any more half rows to check then loop back to 47811 | ||||||
| 47829 | RLC B | Set BC to 32766 for final keyboard half-row | ||||||
| 47831 | IN A,(C) | Read from port 254 into A (i.e. read keyboard) | ||||||
| 47833 | SET 1,A | Set bit 1 of A (i.e. clear pressing of SYMBOL SHIFT) | ||||||
| 47835 | AND 31 | Strip out all but the five bits representing key presses | ||||||
| 47837 | XOR 31 | Invert all of the lowest five bits | ||||||
| 47839 | JR NZ,47843 | If this value is non-zero, then a key has been pressed, so skip ahead to 47843 | ||||||
| 47841 | EXX | Swap registers | ||||||
| 47842 | RET | Return [no key pressed] | ||||||
| 47843 | SRL A | Shift bits right | ||||||
| 47845 | JR C,47850 | If carry flag is set, then this is the key that was pressed, so skip ahead to 47850 | ||||||
| 47847 | INC HL | Advance HL to check next character | ||||||
| 47848 | JR 47843 | Loop back to 47843 | ||||||
| 47850 | LD A,(HL) | Load current character in list of return values string into A as this is the key that was pressed | ||||||
| 47851 | EXX | Swap registers | ||||||
| 47852 | RET | Return [key pressed] | ||||||
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