ModulationScheme

Versaload uses a symmetrical pulse system with multiple pulse lengths, in a similar way to all existing ZX Spectrum, Commodore and Amstrad tape loading systems.

ZX Spectrum ROM tape loader

 ___
|   |___|         489μs, '0' symbol
 _______
|       |_______| 977μs, '1' symbol

ZX Spectrum commercial turbo tape loader (Microsphere)

 _
| |_|               244μs, '0' symbol
 ___
|   |___|           489μs, '1' symbol

Versaload

  __    _    _    __
_|  |__|  or  |__|  |_ '0' symbol
  _____      _       _
_|     |_ or  |_____|  '1' symbol

Note the following important features

1. There is always a signal inversion every bit period.
2. '0' symbols have a signal inversion mid-period too.
3. The '1' symbol is transmitted in half the time of the ROM loader, for the same timings.
4. Versaload meets the DC balance requirements of the audio path.