The CMOS bq2204A SRAM Non-volatile Controller Unit provides all necessary functions for converting up to four banks of standard CMOS SRAM into nonvolatile read/write memory. A precision comparator monitors the 5V VCC input for an out-of-tolerance condi-tion. When out-of-tolerance is detected, the four conditioned chip-enable outputs are forced inactive to write-protect up to four banks of SRAM. During a power failure, the external SRAMs are switched from the VCC supply to one of two 3V backup sup-plies. On a subsequent power-up, the SRAMs are write-protected until a power-valid condition exists. During power-valid operation, a two-input decoder transparently selects one of up to four banks of SRAM.