Routines
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FEAB: Load a block with leading tone.
Used by the routine at FE45. This is mainly a copy of the ROM loading routine.
FEAB INC D Reset zero flag and remember AF
FEAC EX AF,AF'
FEAD DEC D
FEAE DI Disable interrupts while loading (although they are already disabled)
FEAF LD A,$0F Set border to white
FEB1 OUT ($FE),A
FEB3 IN A,($FE) Read the EAR signal
FEB5 RRA
FEB6 AND $20
FEB8 OR $02 Add red border
FEBA LD C,A Remember this state
FEBB CP A Set the zero flag
FEBC RET NZ Return if load abandoned
FEBD CALL $FF52 Get a tape edge
FEC0 JR NC,$FEBC Bail out if we couldn't find one
FEC2 LD HL,$0415 Wait for a while before checking a tape signal. This length is identical to the ROM routine.
FEC5 DJNZ $FEC5
FEC7 DEC HL
FEC8 LD A,H
FEC9 OR L
FECA JR NZ,$FEC5
FECC CALL $FF4E Get a tape edge again
FECF JR NC,$FEBC Bail out if we didn't find one
At this point a leading tone has been found
FED1 LD B,$9C Timing constant
FED3 CALL $FF4E Get a tape edge
FED6 JR NC,$FEBC Bail out if there was none
FED8 LD A,$C6 Was an edge found soon enough?
FEDA CP B
FEDB JR NC,$FEBD No, so loop back again to find one
FEDD INC H Increase the edge pair count
FEDE JR NZ,$FED1 Loop back if more edge pairs need to be retrieved
Get the sync pulse
FEE0 LD B,$C9 Timing constant
FEE2 CALL $FF52 Get a tape edge
FEE5 JR NC,$FEBC Bail out if there wasn't one
FEE7 LD A,B Were two tape edges close enough together to be considered a sync pulse?
FEE8 CP $D4
FEEA JR NC,$FEE0 No, so loop round and check again
The tape block is in sync, so load data
FEEC CALL $FF52 Get a tape edge
FEEF RET NC Exit if there wasn't one
FEF0 LD A,C Switch borders to blue + yellow
FEF1 XOR $03
FEF3 LD C,A
FEF4 LD H,$00 Initialise byte to collect
FEF6 LD B,$E1 Timing constant.
FEF8 JR $FF12 Jump forward to the loading routine
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