Mechanism for automatically adjusting the phase of a transmission strobe

Abstract

A transmission strobe clock signal control mechanism continuously monitors DTE data and transmission strobe clock signals used to strobe the DTE data onto a serial communication link, and automatically adjusts the phase of the transmission strobe clock signal in response to a misalignment between the two signals that exceeds acceptable limits. In a first embodiment, the DTE data signal is sampled by a high speed clock and clocked through a `data sample` shift register. Selected stages of the register, associated with a timing window that contains a transmission strobe clock signal edge, are coupled to an exclusive logic operation circuit, whose output indicates whether all of the data samples in the selected stages of the shift register are the same or not. If not, it is inferred that a data transition too close to the transmission strobe clock signal edge has occurred, necessitating an adjustment of the phase of the transmission strobe clock signal. In a second embodiment, a counter is clocked by high speed clock pulses between transitions in the transmission strobe clock signal and the data signal. A phase control circuit adjusts the phase of the transmission strobe clock signal in response to the number of high speed clock pulses counted not being between prescribed limits.