Dynamite Dan: Routine at FF52

FF52: Get tape signal

Used by the routines at FEAB and FF4E.

Input
B	On input, timing constant. On output, holds the time taken to find an edge change. If found before the timing constant value, a '0' bit was found, otherwise it was a '1' bit.
C	Border colour and previous EAR signal bit

This is similar to the ROM routine LD_EDGE_1 at 05E7.

FF52

LD A,$0B

Wait the required length before sampling a bit

FF54

DEC A

FF55

JR NZ,$FF54

FF57

AND A

Clear carry flag

FF58

INC B

Increment pass counter

FF59

RET Z

Return if a signal wasn't found quickly enough

FF5A

LD A,$7F

Read the tape signal

FF5C

IN A,($FE)

FF5E

RRA

Shift right

FF5F

NOP

The ROM routine returns here; this custom loader does nothing

FF60

XOR C

Mask against expected edge type

FF61

AND $20

Test for the edge

FF63

JR Z,$FF58

Jump back if it wasn't found

At this point, an edge has been found

FF65

LD A,C

Flip border colour

FF66

CPL

FF67

LD C,A

FF68

AND $07

Turn off non-border bits

FF6A

OR $08

Turn off MIC input

FF6C

OUT ($FE),A

Set the border

FF6E

SCF

Set carry flag to denote success

FF6F

RET

All done