Digital decoder for multiple frequency telephone signalling

Claim 3

A method as defined in claim 1 comprising the further step of: inhibiting steps (a) to (d) in the presence of a signal having a period which exceeds a predetermined time.

Claim 6

An electronic circuit for identifying, within predetermined frequency limits, a signal selected from a family of signals having distinctly different predetermined frequencies, comprising: counting means for counting each cycle of the signal, timing means for generating a timing signal having a time interval, after a predetermined plurality of cycles have been counted by said counting means, said timing means including means for inhibiting said counting means at the end of said time interval, decoding means for decoding the output of the counting means so that the frequency of the signal is identified as being within said limits when the counted total of cycles falls within one of a plurality of permissible count ranges in a series of count ranges.

Claim 7

An electronic circuit for identifying, within predetermined frequency limits, a signal selected from a family of signals having distinctly different predetermined frequencies, comprising: counting means for counting each cycle of the signal, timing means for generating a timing signal having a time interval, after a predetermined plurality of cycles have been counted by said counting means, said timing means including means for inhibiting said counting means at the end of said time interval, decoding means for decoding the output of the counting means so that the frequency of the signal is identified as being within said limits when the counted total of cycles falls within one of a plurality of permissible count ranges in a series of count ranges.

Claim 8

An electronic circuit as defined in claim 4 further comprising: reset means for resetting the counting means and the timing means in the absence of the signals having cycles of less than a predetermined duration of time.

Claim 9

An electronic circuit for idenfitying, within predetermined frequency limits, a pair of lower and upper signalling frequency signals received from a telephone transmission facility, wherein the lower signalling frequency signal is one of a predetermined plurality of signals in a lower frequency group and the upper signalling frequency signal is one of a predetermined plurality of signals in an upper frequency group, comprising: filtering means for segregating the lower and upper signalling frequency signals, one from the other, a lower group counting means for counting the cycles of the lower signal for storing the resultant count on receiving a first inhibit signal and for resetting to a 0 output on receiving a reset signal, a first timing means for generating a first timing signal having a first time interval in response to a predetermined plurality of cycles of the lower signal being counted, and for providing the first inhibit signal at the end of the first time interval, a first reset means for resetting the lower group counting means and the first timings means in the absence of a lower signal having cycles of less than a first predetermined duration of time, an upper group counting means for counting the cycles of the upper signal, for storing the resultant count on receiving a second inhibit signal, and for resetting to a 0 count on receiving a second reset signal, a second timing means for generating a second timing signal having a second time interval, in response to a predetermined plurality of cycles of the upper signal being counted and for Providing the second inhibit signal at the end of the second time interval, a second reset means for resetting the upper group counting means and the second timing means in the absence of an upper signal having cycles of less than a second predetermined period of time, decoding means for identifying said lower and upper signalling frequencies according to a translation of the respective counts associated therewith, after the first and second time intervals and in the continuance of lower and upper signals being received by the lower and upper group identifying circuits.

Claim 10

An electronic circuit for idenfitying, within predetermined frequency limits, a pair of lower and upper signalling frequency signals received from a telephone transmission facility, wherein the lower signalling frequency signal is one of a predetermined plurality of signals in a lower frequency group and the upper signalling frequency signal is one of a predetermined plurality of signals in an upper frequency group, comprising: filtering means for segregating the lower and upper signalling frequency signals, one from the other, a lower group counting means for counting the cycles of the lower signal for storing the resultant count on receiving a first inhibit signal and for resetting to a 0 output on receiving a reset signal, a first timing means for generating a first timing signal having a first time interval in response to a predetermined plurality of cycles of the lower signal being counted, and for providing the first inhibit signal at the end of the first time interval, a first reset means for resetting the lower group counting means and the first timings means in the absence of a lower signal having cycles of less than a first predetermined duration of time, an upper group counting means for counting the cycles of the upper signal, for storing the resultant count on receiving a second inhibit signal, and for resetting to a 0 count on receiving a second reset signal, a second timing means for generating a second timing signal having a second time interval, in response to a predetermined plurality of cycles of the upper signal being counted and for Providing the second inhibit signal at the end of the second time interval, a second reset means for resetting the upper group counting means and the second timing means in the absence of an upper signal having cycles of less than a second predetermined period of time, decoding means for identifying said lower and upper signalling frequencies according to a translation of the respective counts associated therewith, after the first and second time intervals and in the continuance of lower and upper signals being received by the lower and upper group identifying circuits.