Abstract: The inventive method and apparatus for enabling an operator terminal to control remotely a computer system enables data to be transmitted over long distances in a highly stable manner by deleting a message if a mismatch occurs between the data and error checking information contained in the received data. The computer is then subsequently returned to its last valid state to prevent the system from inadvertently becoming disrupted either by the terminal or the computer being disconnected from the transmission line during an idle condition of the system, or by invalid data being received, such as where the transmission line becomes disrupted inadvertently. A voltage controlled oscillator generates a stable reference clock signal, and a phase detector responds to the stable reference clock signal and to the pixel clock signal for, in turn, controlling the oscillator.