Start bit detection circuit

Claim 1

In a receiver of serial asynchronous electrical data signals, the signals being communicated to the receiver through a transmission medium containing ambient electrical noise signals having polarities identical to those of the data signals, amplitudes greater than a minimum established for the data signals and durations substantially less than a minimum established for the data signals, a circuit for selectively detecting a first data signal in a chain thereof, the circuit comprising: timing means operably coupled to a transmission medium for initiating a timed period, represented by a timing pulse, in response to the leading edge of an electrical signal having the same polarity as a data signal and having an amplitude greater than an established data signal minimum, the timing pulse having a duration less than an established data signal minimum but greater than the duration of a typical noise signal, said timing means being a monostable multivibrator triggerable to an unstable state by an electrical signal having the same polarity as a data signal and having an amplitude greater than the established data signal minimum, said timing means also being responsive to any subsequent electrical signal occurring within the timed period to thereby extend the timing pulse one full timed period from the instant the latter electrical signal is applied to said timing means; pulse shaping means operably coupled to said timing means for generating a pulse of relatively short duration at the trailing edge of a timing pulse initiated by said timing means; gating means operably coupled to the transmission medium and to said pulse shaping means for generating a start pulse upon the coincidence of a signal from the transMission medium and a pulse from said shaping means, the start pulse being indicative of the receipt of the first in a chain of incoming data signals; and a trigger inhibitor responsively coupled to said gating means and operably coupled to said timing means to prevent the retriggering of said timing means subsequent to the generation of a start pulse by said gating means for a predetermined time.