The X88064 is a high speed byte wide microperipheral device with eight 1K byte blocks of E2PROM and can be directly connected to industry standard high performance microprocessors. This peripheral provides two levels of memory write control, the standard Software Data Program (SDP) control and Block Lock. Block Lock provides a higher level of memory write control above SDP. This allows the software developer to partition any or all of the eight 1K byte blocks as In-Circuit Programmable ROM (ICPROM). Once locked, a block of memory must first be unlocked before being written. Not even a write operation using the SDP sequence will change the contents of a locked block. Since a distinct, 6 byte, software command sequence locks and unlocks the memory, the software developer has complete control of the memory contents.