Abstract: A digital data recovery apparatus for extracting phase encoded data from mass storage devices is disclosed. By selective strobing of the data string at a frequency determined by the incoming data rate of data already read, a continuously updated data "window" is generated. The data synchronization, clock control and frequency averaging of the previously read data is accomplished without the use of any analog circuitry.

Abstract: A programmable data envelope detector indicates the presence of phase encoded data being transmitted to or received from a data storage medium. The detector generates an output signal at a predetermined time after detecting the presence of data and continues to provide such output signal for a predetermined time after detecting the end of data. The detector comprises a data pulse detector, three-count up-down counter, two multicount four-bit up-down counters, a microprogrammable control store and decoder, a compare circuit, and a latch circuit. The time periods at which the latch circuit generates the output signal are different depending upon the nature of the data transfer operation, such time periods corresponding to different microinstructions in the control store.