Hazard-free circuitry for determining full and empty conditions in

Abstract

In a first-in-first out memory, at least one data item is stored, and a write counter is incremented in response to the storing of each data item as it is stored into the memory. A full condition counter is also incremented in response to the writing of each data item. The at least one data item is also read from the memory, and a read counter is incremented in response to the reading of each data item from the memory. An empty condition counter is also incremented in response to the reading of each data item from the memory. In order to assure that the empty and full flag signals are not generated simultaneously, the full flag signal is generated in response to a count within the full condition counter that leads a count within the empty condition counter by a first prescribed difference. The empty flag signal is generated in response to the count within the full condition counter lagging the count within the empty condition counter by a second prescribed difference. As a result, the full flag signal and the empty flag signal are never simultaneously generated so long as the full condition counter and the empty condition counter each have at least one more state than the read counter and the write counter.