Zero fall-through time asynchronous fifo buffer with nonambiguous

Abstract

A First In First Out shift register memory system (10) with a plurality of memory word registers (50) having data inputs connected to a common data-in bus (16), and a plurality of data outputs connected to a common data-out bus (22). A read address ring counter (36) and write address ring counter (32) are responsive to respective read and write pulses to sequentially perform memory read and write operations. A comparator (40) compares the address outputs of the ring counters (36, 32) for equality. A read and a write signal generator (80, 60) are provided for producing respective read and write pulses in response to input transitions of read and write commands. A last operation R/W flip-flop (70) maintains an account of the last read and write memory operation processed by the system. Read and write enable latches (90, 66) are responsive to the comparator (40) output indication of address equality, and responsive to the last operation R/W flip-flop (70) output indication of the last memory operation to prevent the reading of the memory (48) by read pulses when empty, and the writing of the memory (48) by write pulses when full.