ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper introduces a frequency scan/following scan twoway carrier acquisition method for USB and its following scan slope decision algorithm. Some measures are used to improve twoway acquisition speed such as selecting initiation direction and returning to zero in the shortest path, which can be implemented by software. Theoretic analysis, mathematical expression, design method and experiment results are provided. Practical engineering application shows the twoway acquisition using this new method has many advantages such as fast speed, low cost and programmability. The method has been used in Chinese USB system widely.