The Microchip Technology Inc. 93LCS56/66 are low voltage Serial Electrically Erasable PROMs with memory capacities of 2K bits/4K bits respectively. A write protect Register is included in order to provide a user defined region of write protected memory. All memory locations greater than or equal to the address placed in the write protect register will be protected from any attempted write or erase operation. It is also possible to protect the address in the write protect register permanently by using a one time only instruction (PRDS). Any attempt to alter data in a register whose address is equal to or greater than the address stored in the protect register will be aborted. Advanced CMOS technology makes this device ideal for low power non-volatile memory applications