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 8751H-8 is identical to the 8751H 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.
The 8052AH is an enhanced version of the 8051AH. It is backwards compatible with the 8051AH and is fabricated with HMOS II technology. The 8052AH enhancements are listed in the table below. Also refer to this table for the ROM, ROMless and-EPROM versions of each product.

■ High Performance HMOS Process
■ Internal Timers/Event Counters
■ 2-Level interrupt Priority Structure
■ 32 1/0 Lines (Four 8-Bit Ports)
■ 64K External Program Memory Space
■ Security Feature Protects EPROM Parts Against Software Piracy
■ Boolean Processor
■ Bit-Addressable RAM
■ Programmable Full Duplex Serial Channel
■ 111 Instructions (64 Single-Cycle)
■ 64K External Data Memory Space
■ Extended Temperature Range (–40”C to +85”C)