spandsp 3.0.0
Asynchronous bit stream processing

What does it do?

The asynchronous processing module converts between hard bit streams, containing start-stop framed asynchronous characters, and actual characters.

It supports:

  • 5, 6, 7, 8 or 9 bit characters.
  • Odd, even, mark, space or no parity.
  • 1 or 2 stop bits.
  • V.14 rate adaption.

V.14 rate adaption is a mechanism where some stop bits may be omitted within a data burst. This is needed to make inherently synchronous modems, like V.22 up to V.34, behave like an asynchronous modem, and interface to the "RS232C" world. Currently it only supports this for bit stream to character conversion.

Soft bit processing is outside the scope of this module. For truly asynchronous modems, such as V.21, soft bit processing can produce more robust results, and may be preferrable.

The transmitter

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The receiver

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Because the input to this module is a hard bit stream, any symbol synchronisation and decoding must occur before this module, to provide the hard bit stream it requires.