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Load routines |
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Used by the routine at 802F.
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8000 | INC SP | Place the address 0000 on the stack above the current return address, so the Spectrum will reset if there's a loading error | ||||||
8001 | INC SP | |||||||
8002 | EX (SP),HL | |||||||
8003 | LD H,$00 | |||||||
8005 | LD L,H | |||||||
8006 | EX (SP),HL | |||||||
8007 | DEC SP | |||||||
8008 | DEC SP | |||||||
8009 | LD A,$06 | |||||||
800B | CALL $8011 | Listen for one edge | ||||||
800E | RET NC | Return if no edge was found within the time limit | ||||||
This entry point is also used by the routine at 802F.
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800F | LD A,$0B | Wait a bit | ||||||
8011 | DEC A | |||||||
8012 | JR NZ,$8011 | |||||||
8014 | AND A | Reset the carry flag | ||||||
8015 | INC B | Have we run out of time to find an edge? | ||||||
8016 | RET Z | Return with the carry flag reset if so | ||||||
8017 | LD A,$7F | Collect an EAR port reading in bit 6 of A | ||||||
8019 | IN A,($FE) | |||||||
801B | RRA | Move it to bit 5 of A | ||||||
801C | AND A | In the analogous ROM routine, the instruction here is 'RET NC', causing a return if BREAK was pressed; in this routine, that behaviour is disabled (pressing BREAK does nothing) | ||||||
801D | XOR C | Compare this EAR port reading with the previous one | ||||||
801E | AND $20 | |||||||
8020 | JR Z,$8015 | Jump back if they are the same (i.e. no edge was found) | ||||||
8022 | LD A,C | Alternate the border colour | ||||||
8023 | CPL | |||||||
8024 | LD C,A | |||||||
8025 | AND $07 | |||||||
8027 | OR $08 | |||||||
8029 | OUT ($FE),A | |||||||
802B | SCF | Signal: an edge was found within the time limit | ||||||
802C | RET | Return with B indicating the time taken to find the edge |
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