Load routines
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8000: Collect one bit from tape
Used by the routine at 802F.
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 After the fast code block has loaded, this instruction is changed to 'LD A,$11' for the standard speed code block
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.
800F LD A,$0B Wait a bit; after the fast code block has loaded, this instruction is changed to 'LD A,$16' for the standard speed code block
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; that behaviour is disabled when loading the fast code block (pressing BREAK does nothing), but after the fast code block has loaded, this instruction is changed to 'RET NC' for the standard speed code block
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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