Método de alinhamento da frequência de oscilação livre em um terminal de vídeo

摘要

A free running frequency alignment method in a video display having a sync generator comprising a first oscillator having a first frequency and a second oscillator having a second frequency. The first oscillator is phase modulated by the second oscillator which has a free running frequency different from a standard frequency. The free running frequency of the first oscillator is to be controllably aligned to the standard frequency by a method comprising the steps of applying a frequency determining initial control value to the first oscillator and measuring an average free running frequency responsive to the initial control value. An absolute difference frequency is calculated between the average frequency and the standard frequency. The absolute difference frequency is tested for a frequency value less than a predetermined value which signifies an aligned condition. If the difference frequency is less than the predetermined value the alignment is complete. If the difference frequency is greater than the predetermined value the alignment is continued and a new control value is generated responsive to the difference. The new control value is applied to the first oscillator and the steps of average frequency measurement, absolute difference frequency calculation and difference frequency value testing are repeated until alignment is achieved. Upon failure of the difference frequency test, a counter is incremented and the count examined to determine if a predetermined number of alignment attempts have been exceeded. Upon exceeding the predetermined number the alignment is determined to have failed and the alignment is ended.