Mode recognition for vertical countdown

In a method for vertical synchronization of a television system which digitally locally develops vertical sync pulses, derives vertical sync pulses from a received television signal, and selectively applies the locally developed sync pulses or the derived sync pulses to a vertical sweep system of the television system, the improvement comprising:

• maintaining a first count representing accumulated vertical field time intervals and resetting said count periodically.
• maintaining a second count representing accumulated derived vertical sync pulses;
• resetting said second count in response to said first count reaching a first predetermined number;
• toggling a logic device in response to said first count reaching said first predetermined number;
• resetting said logic device in response to said second count reaching a second predetermined number;
• and
• signaling said television receiver to apply the locally developed sync pulses in response to said logic device being toggled to a predetermined one of its states, whereby said signaling will occur unless said second predetermined number of derived sync pulses is reached before said first predetermined number is reached.

In a method for vertical synchronization of a television system which digitally locally develops vertical pulses, derives vertical sync pulses from a received television signal, and selectively applies the locally developed sync pulses or the derived sync pulses to a vertical sweep system of the television system, the improvement comprising:

• detecting noise in said received signal including defining a first time window during each of a plurality of vertical fields, detecting any of said derived vertical sync pulses from said received television signal which occur during said first time window, and actuating a logic device to provide a noisy signal indication in response to the detection of said pulses during said first time window;
• detecting a low sync pulse signal strength in said received signal, including defining a second time window having a relationship to the vertical sync frequency of the television system, detecting any of the derived vertical sync pulses which occur during said second time window and an absence of a first predetermined number of said derived vertical sync pulses which occur during said second time window, and actuating said logic device in response to the detection of said absence of pulses;
• and
• signalling said television system to apply said locally generated sync pulses to said vertical sweep system in response to said logic device being actuated, whereby the logic device is used for signaling a condition when either the noise or low signal strength is detected.

In a vertical synchronization system for a television system which digitally locally develops vertical sync pulses and derived vertical sync pulses from a received television signal and includes means for selectively applying the locally developed sync pulses or the derived sync pulses to a vertical sweep system of the television, the improvement comprising:

• means for defining a time window having a beginning and an end, said means for defining a time window including means for accumulating a count of vertical field time intervals and means for resetting said count when it reaches a predetermined number;
• means for detecting derived vertical sync pulses which occur during said time window and for detecting whether a predetermined number of said derived vertical sync pulses occur during said time window, said means for detecting including means for accumulating a count of derived vertical sync pulses occurring during said time window and means for resetting said count of derived vertical sync pulses to a preset starting count at the close of said time window;
• means responsive to said means for detecting for signaling said television system to apply said locally developed sync pulses to said vertical sweep system;
• said means for detecting including a logic device, means for enabling said logic device in response to the beginning of said time window and for triggering said logic device to generate a signal when said time window ends.

In a vertical synchronization system for a television system which digitally locally develops vertical sync pulses and derived vertical sync pulses from a received television signal and includes means for selectively applying the locally developed sync pulses or the derived sync pulses to a vertical sweep system of the television, the improvement comprising:

• means for defining a time window having a beginning and an end, said means for defining a time window including means for accumulating a first count of vertical field time intervals and means for resetting said count when it reaches a first predetermined number;
• means for detecting derived vertical sync pulses which occur during said time window and for detecting whether a second predetermined number of said derived vertical sync pulses occur during said time window;
• and
• means responsive to said means for detecting for signalling said television system to apply said locally developed sync pulses to said vertical sweep system;
• said means for detecting including a logic device, means for enabling said logic device in response to the beginning of said time window and for triggering said logic device to generate a signal when said time window ends,
• said means for defining including a first counter coupled to receive signals at the vertical field rate and providing said first count and means for resetting said first counter periodically;
• said means for detecting including a second counter coupled to receive the derived vertical sync pulses, means for resetting said second counter in response to said first count reaching said first predetermined number, said logic device having at least two states, means for toggling said logic device in response to said first count reaching said first predetermined number, means for resetting said logic device to one state in response to said second counter reaching said second predetermined number, said logic device providing an output to said means for signaling said television system in response to said logic device reaching another state, whereby said signalling occurs unless said second predetermined number of derived sync pulses is counted before said first number of vertical field time intervals is counted after said logic device is reset.