A power supply lockout circuit that prevents corruption of non-volatile writable memory data is described. The power supply (112) lockout circuit monitors the power supply signals from several power supplies. The power supply lockout circuit locks out commands writing to the non-volatile writable memory when any one of the monitored power supply signals coupled to the non-volatile writable memory is below a specified signal level. The power supply lockout circuit includes a detector (102) which provides a lockout signal to the non-volatile writable memory when a power supply signal is less than a prespecified voltage. The power supply lockout circuit also includes a sampling circuit (110) which provides other lockout signals to the non-volatile writable memory when a different power supply signal is less than a reference voltage.
