Contact Sam Cruise: Routine at 80BC

80BC: Prepare to load the standard speed code block

This section of code is executed immediately after the fast code block has loaded. First of all, it modifies the loading routines at 8000 and 802F to make them suitable for loading a standard speed block.
80BC	LD B,$0B	Do the 11 POKEs in the POKE table at 8100; these POKEs convert the fast loading routines into standard speed loading routines, ready for the final code block on the tape
80BE	LD D,$80
80C0	LD HL,$8100
80C3	LD E,(HL)
80C4	INC L
80C5	LD A,(HL)
80C6	LD (DE),A
80C7	INC L
80C8	DJNZ $80C3
Now a checksum of the bytes at addresses 8100-81AB (just loaded from tape) is calculated.
80CA	LD L,B	HL=8100
80CB	LD E,B	DE=0000
80CC	LD D,B	DE=0000
80CD	LD B,$AC	Create 'checksums' in A and E of the 172 bytes at addresses 8100-81AB
80CF	LD A,(HL)
80D0	ADD A,E
80D1	LD E,A
80D2	LD A,(HL)
80D3	XOR D
80D4	LD D,A
80D5	INC L
80D6	DJNZ $80CF
80D8	LD L,$28	HL=8128
80DA	CP $4B	Is the checksum in A correct?
80DC	JP NZ,$0000	Reset the Spectrum if not
80DF	LD A,E	Is the checksum in E correct?
80E0	CP $AF	Is the checksum in E correct?
80E2	JP Z,$8116	Jump if so
80E5	JP $0000	Otherwise reset the Spectrum