The MCS@51 controllers are optimized for control applications. Byte-processing and numerical operations on small data structures are facilitated by a variety of fast addressing modes for accessing the internal RAM. The instruction set provides a convenient menu of 8-bit arithmetic instructions, including multiply and divide instructions. Extensive on-chip support is provided for one-bit variables as a separate data type, allowing direct bit manipulation and testing in control and logic systems that require Boolean processing. The 8751H is an EPROM version of the 8051AH. It has 4 Kbytes of electrically programmable ROM which can be erased with ultraviolet light. His fully compatible with the 8051AH but incorporates one additional feature: a Program Memory Security bit that can be used to protect the EPROM against unauthorized readout. The 8751 H-8 is identical to the 8751 H but only operates up to 8 MHz. The 8051AHP is identical to the 8051AH with the exception of the Protection Feature. To incorporate this Protection Feature, program verification has been disabled and external memory accesses have been limited to 4K.