Synchronizing means

Synchronising means for synchronising with a periodically repeating reference signal the change of level of an input signal capable of assuming either one of a first and second level, comprising a source of said periodically repeating reference signal, a source of said input signal, a bistable device having first and second inputs and an output and capable of assuming a first stable state in response to the first level of input signal applied to said first input and of assuming a second stable state in response to the second level of input signal applied to said first input and enabled periodically by said reference signal applied to said second input to respond to the level of the input signal, said bistable device producing at said output an output signal having a first level representing said first stable state and a second level different from said first level and representing said second stable state, means responsive to a level of output signal intermediate said first and second levels representing an unstable condition of said bistable device, resulting from a level of input signal intermediate said first and second levels of input signal during the period the bistable device is enabled to respond, to generate a stop signal and means for applying said stop signal to said source of periodically repeating reference signal to interrupt the reference signal at a predetermined point in its periodicity and before the bistable device is next enabled, until the bistable device assumes a stable condition.