Dual-port read/write ram with single array

Abstract

A single-array memory employs a novel storage cell providing dual read/write access via either an 'A'-side or a 'B'-side. The storage cell uses a unique circuit in which read current is borrowed during writing into the cell. Asymmetrical read/write delay circuitry is provided to avoid overwriting the contents of a storage cell during the read-to-write transition. Row-selection decoders use Schottky-clamping diodes in a way which provide an equivalent oscillation-damping capacitance at the base of the selected-row driver transistor. The single-array memory can be advantageously used as part of a single-chip VLSI four-port register file permitting simultaneous reading and/or writing of registers from any of two read ports or two write ports, respectively. Unidirectional busses connect each storage cell to each of the four ports.