Memory cell with known state on power-up

Abstract

Apparatus for forcing a memory cell to a known state upon power-up includes circuitry for providing two signals PWRUP and PWRUPB which are used during chip power-up. At power-up, as V.sub.CC rises from 0 volt to 3.5 volts, the PWRUP signal follows V.sub.CC and the PWRUPB signal maintains 0 volts. The PWRUP and PWRUPB signals are used to drive the gates of P-Channel and N-Channel MOS transistors, respectively, including pass gates connected between word line driver circuits and bit line driver circuits driving the word lines and bit lines associated with the memory cells. In addition, the PWRUPB signal is used to drive P-Channel MOS pullup transistors connected between the word lines and V.sub.CC and the bit lines and V.sub.CC. During power-up, the pass gates are disabled, disconnecting the word lines and bit lines from their drivers. The word lines and bit lines are forced to follow the rise of V.sub.CC by the P-Channel pullup transistors. When V.sub.CC reaches its desired value, the PWRUP signal goes to 0 volts and the PWRUPB signal goes to V.sub.CC, thus turning on the pass gates to connect the word line and bit line driver circuits to the word lines and bit lines. The V.sub.CC final PWRUPB signal turns off the P-Channel MOS pullup transistors connected between the word lines and V.sub.CC and the bit lines and V.sub.CC.