Monitor adjustment by data manipulation

An apparatus for providing display data to a monitor comprising:

• a frame memory for storing one or more frames of display data for display on a display screen;
• an output clock configured to provide timing for reading display data from the frame memory;
• and
• an output clock control means for varying the timing of the output clock according to a reference waveform applied to the output clock, wherein the varying the timing of the output clock comprises the steps of:
• (a) generating output clock pulses for reading display data out of the frame memory, the timing and frequency of the output clock pulses being a function of two separate input signals;
• (b) frequency dividing the output clock pulses and producing an output horizontal sync pulse every predetermined number of clock pulses;
• (c) phase comparing both an input horizontal clock signal from an external source that also supplies the display data to the frame memory and the output horizontal sync pulse to produce a phase error signal representing the difference in phase between the output horizontal sync pulse and the horizontal clock signal and supplying the phase error signal as a first one of the two separate input signals for step (a);
• and applying a reference signal as a second one of the two separate input signals for step (a) for varying the period and timing of the clock pulses as a function of the waveform of the reference signal.

A method for manipulating an image displayed on a monitor comprising the steps of:

• storing at least one frame of display data in a frame memory;
• displaying an image on a display screen by reading and displaying the display data at a rate of an output clock;
• varying the timing of the output clock according a reference waveform, wherein the varying the timing at which the display data are read out from the frame memory to the display screen comprises the steps of:
• (a) generating output clock pulses for reading display data out of the frame memory, the timing and frequency of the output clock pulses being a function of two separate input signals;
• (b) frequency dividing the output clock pulses and producing an output horizontal sync pulse every predetermined number of clock pulses;
• (c) phase comparing both an input horizontal clock signal from an external source that also supplies the display data to the frame memory and the output horizontal sync pulse to produce a phase error signal representing the difference in phase between the output horizontal sync pulse and the horizontal clock signal and supplying the phase error signal as a first one of the two separate input signals for step (a);
• and applying a reference signal as a second one of the two separate input signals for step (a) for varying the period and timing of the clock pulses as a function of the waveform of the reference signal.