TV Receiver with multiplexed microprocessor keyboard scanning and channel number display

摘要

A system eliminates digital switching video noise by performing several microprocessor controlled operations in a television receiver during the vertical retrace interval. A microprocessor maintained in an idle state until detection of a vertical retrace pulse initiates channel selector keyboard scan, channel number display update, and phase locked loop tuning information update during the vertical interval by multiplexing control outputs therefrom on a limited number of microprocessor IC pins. This approach provides for the regular and continuous updating of television receiver operating parameters while eliminating digital switching noise from the receiver's video display generated by the transfer of digital data representing the aforementioned operating parameters.