The SST89E5xxRD2 and SST89V5xxRD2 are members of the FlashFlex51 family of 8-bit microcontroller products designed and manufactured with SST's patented and proprietary SuperFlash CMOS semiconductor process technology. The split-gate cell design and thick-oxide tunneling injector offer significant cost and reliability benefits for SST's customers. The devices use the 8051 instruction set and are pin-for-pin compatible with standard 8051 microcontroller devices. The devices come with 16/24/40/72 KByte of on-chip flash EEPROM program memory which is partitioned into 2 independent program memory blocks. The primary Block 0 occupies 8/16/32/64 KByte of internal program memory space and the secondary Block 1 occupies 8 KByte of internal program memory space. The 8-KByte secondary block can be mapped to the lowest location of the 8/16/32/64 KByte address space; it can also be hidden from the program counter and used as an independent EEPROM-like data memory.