The Amstrad's cassette electronics converts the amplitude of the sound (a analogue signal) into a "0" or "1" measurement (a digital signal). This measurement can then be read from bit 7 of port B of the PPI 8255 IC.
[[Image:conv.gif]]
''Fig 8. This image shows the conversion of the audio waveform from the cassette into the digital representation by the Amstrad's cassette electronics. i.e. audio waveform (on cassette) -> Amstrad's cassette electronics -> 0 and 1 measurements''
* if the amplitude is 0..128, then the final measurement will be "1".
* if the amplitude is -128..0 then the final measurement will be "0".
=== Writing ===