METHOD AND APPARATUS FOR OPERATING A MICROPROCESSOR IN SYNCHRONISM WITH A VIDEO SIGNAL

摘要

A microprocessor is provided in a television receiver which is responsive to a clock signal phase locked to a recurrent signal component of a composite video signal, such as a horizontal line rate signal component. The clock signal frequency is chosen to be an integer multiple of the recurrent signal component and to enable the microprocessor to execute an integer number of uniform instruction cycles during an integer number of periods of the recurrent signal component. The execution of the instruction cycles is brought into a real time phase alignment with the recurrent signal component by causing the microprocessor to execute an instruction during a time interval which is greater than the time required to execute one of the uniform insturction cycles. The phase of subsequently executed uniform instruction cycles is shifted in this manner until signal sampling indicates that the desired phase relationship has been achieved.