Synchronization system for variable line length facsimile transceivers
AssigneeFaxon Communications Corporation
InventorCarl R. Kolker
Life of this patent
Estimating the term…
Abstract
In a facsimile transceiver, an independent, high frequency precision oscillator precisely times the generation of synchronizing pulses which are transmitted to a remote, similar transceiver. An identical precision oscillator assures that the receiver employs the transmitted synchronizing pulse to generate an accurate representation of the information being transmitted. The precision oscillators generate much lower frequency clocking signals, which remain in synchronism during the transmission of a "page" of data.
Claims14
In a raster scan facsimile system utilizing transceivers having means for modulating and demodulating video information on a carrier signal and hving means for creating a raw first signal whose initiation indicates the end of a raster line and whose duration, determined by a predetermined number of cycles of a controllable oscillator, indicates the magnitude of vertical displacement between successive scan lines, successive raw first signals being asynchronous, a combination for better synchronizing a first transceiver functioning in a transmitting mode as a transmitter with a remote transceiver functioning in a receiving mode as a receiver comprising, in each transceiver:
- (a) precision oscillator means for creating a first clock signal whose frequency is an integral fraction of said precision oscillator frequency;
- and a second clock signal whose frequency is an integral fraction of said first clock signal;
- and
- (b) control signal generating means including counting means coupled in the transmitting mode to the controllable oscillator and to said precision oscillator means for generating control signals in response to the raw first signal, the initiation of said control signals being synchronized to said first and second clock signals and the duration of said control signals being related to said first signal, said counting means generating a first operating signal after counting a first predetermined number of first clock signals and a second operating signal after counting a second predetermined number of first clock signals for precise control of the duration of said operating signals;
- and
- (c) whereby the raw first signal is employed only to indicate the approximate start and duration of said control signals in a transceiver when functioning as a transmitter or a received signal when functioning as a receiver, and each scan of the image is controlled by said precision oscillator means for better synchronizing with remote transceivers so that uncertainties as to the time of termination or precise duration of a raw first signal do not affect the generation of control and operating signals.
In a raster scan facsimile system utilizing transceivers having means for modulating and demodulating video information on a carrier signal and having means for creating and transmitting an EOL based signal whose occurrence indicates the end of a raster line and whose duration, determined by a predetermined number of controllable oscillator means cycles, controls the size of the vertical scan increments, successive EOL signals being asynchronous, a combination for better synchronizing a first transceiver functioning as a transmitter with a second transceiver functioning as a receiver comprising, in each transceiver:
- (a) precision oscillator means including means for deriving a first clock signal whose frequency is an integral fraction of said precision oscillator frequency;
- and a second clock signal whose frequency is an integral fraction of said first clock signal;
- (b) counting means connected to said precision clock means for generating an operating signal after the predetermined number of first clock signals;
- (c) vertical scan incrementing means coupled to the controllable oscillator and said counting means, and responsive to the EOL signal when operating as a transmitter and to a received detected delayed SYNC signal derived from a received EOL based signal when operating as a receiver and said first clock signal for producing a vertical gate signal whose duration is determined by said operating signal and is related to the duration of the EOL signal when operating as a transmitter, or to the duration of the detected delayed SYNC signal when operating as a receiver, and;
- (d) horizontal scan control means coupled to the controllable oscillator and said precision clock means and responsive to the EOL signal when operating as a transmitter and to a received detected delayed SYNC signal when operating as a receiver and said second clock signal for synchronizing the start of horizontal sweep to said precision clock signal;
- whereby each scan of the image is referred to said precision clock means for better synchronization with remote transceivers so that each vertical incrementing step and the start of each scan line are under coarse control of an EOL signal and under fine control of said precision clock means.
In a raster scan facsimile system utilizing transceivers having means for modulating and demodulating video information on a carrier signal and having means for creating an EOL signal having a first and second duration range whose initiation indicates the end of a scan line, and duration, determined by a first and second predetermined number of controllable oscillator means cycles, controls the magnitude of vertical displacement between successive scan lines, successive EOL signals being asynchronous, a combination for better synchronizing a first device functioning as a transmitter with a remote device functioning as a receiver, the receiver comprising:
- precision oscillator means for producing a first clock signal whose frequency is an integral fraction of said precision oscillator frequency;
- and a second clock signal whose frequency is an integral fraction of said first clock signal;
- detecting and delay means coupled to receive the output of a device functioning as a transmitter and operable in response to a received SYNC signal related to the EOL signal for producing a detected delayed SYNC signal having a duration range corresponding to the duration range of the received SYNC signal;
- and
- control signal generating means coupled to said detecting and delay means and to said precision clock means for generating a control signal whose initiation is synchronized to at least one of said first and second clock signals, and whose duration is selected by the duration range of said detected delayed SYNC signal,
- whereby each received scan of the image is referred to said precision oscillator for better synchronizing with the remote transmitting device so that uncertainties as to the precise time of termination and duration of the received SYNC signal do not affect the generation of control signals.
In a raster scan facsimile system transceiver capable of alternatively operating as a transmitter and as a receiver, including controllable oscillator means for communicating information between a transmitter and receiver, apparatus to improve synchronism between a transceiver functioning as a transmitter and remote transceivers functioning as receivers comprising, in combination:
- (a) clocking means including precision oscillator means for creating a first clock signal whose frequency is an integral fraction of said precision oscillator frequency;
- and a second clock signal whose frequency is an integral fraction of said first clock signal;
- (b) first signal generating means including means coupled to the controllable oscillator and operable in the transmitting mode to create a raw synchronizing signal (EOL), of a duration corresponding to a first or second predetermined number of controllable oscillator cycles;
- and
- (c) second signal generating means including means coupled to said first signal generating means, the controllable oscillator means and said clocking means and operable in the transmitting mode to create a precision synchronizing signal (SYNC) for transmission to remote transceivers operating as receivers whereby the transmitted synchronizing signal (SYNC) is initiated and terminated under the control of said clocking means.
In a raster scan facsimile system transceiver capable of alternatively operating as a transmitter and as a receiver, including controllable oscillator means for communicating information between a transmitter and receiver, apparatus to improve synchronism between a transceiver functioning as a receiver and a remote transceiver functioning as a transmitter comprising, in combination:
- (a) clocking means including precision oscillator means for creating a first clock signal whose frequency is an integral fraction of said precision oscillator frequency;
- and a second clock signal whose frequency is an integral fraction of said first clock signal;
- (b) first signal generating means coupled to receiving circuits to receive a transmitted synchronizing signal (SYNC) for creating a raw synchronizing signal (DET'D SYNC), of a duration corresponding to a first or second predetermined number of controllable oscillator cycles at the transmitter;
- (c) second signal generating means including delay means coupled to said first signal generating means for creating a delayed synchronizing signal (DET'D DLY'D SYNC);
- and
- (d) third signal generating means coupled to said second signal generating means and said clocking means for producing a precision synchronizing signal (NEW SYNC) in the transceiver operating as a receiver whereby the transmitter synchronizing signal (SYNC) controls the initiation of a precision synchronizing signal that is terminated under the control of said clocking means.
Dependencies are inferred from the claim text.