Frequency independent asynchronous clock crossing fifo

Abstract

A clock crossing FIFO capable of functioning regardless of relative clock frequencies on the write and read sides. Toggle signals are utilized to cross the clock boundaries. The number of write counts which have been accrued but not acknowledged by the read side are tracked, and this number is stored as of the issuance of a write toggle. Upon toggle receipt on the read side, this number is latched as a measure of the number of data units which can be read from the FIFO. At the same time, the toggle is returned to the write side for decrementing the number of write counts outstanding by the number conveyed to the read side. Similar circuitry is employed for conveying to the write side circuitry the number of data units which have been read by the read side circuitry. The presently disclosed FIFO and associated circuitry operates independent of relative clock speeds, and the particular size of the FIFO is scalable.