ABSTRACT
This chapter examines the architecture and memory organization of the 8051 microcontroller. It also discusses all subsystems which are available in the standard versions. The 8051 microcontroller has 4K bytes on-chip Program Memory (factory mask-programmable ROM). The device also possesses 128 bytes of internal Data Memory. The 8031 microcontroller lacks internal Program Memory. All microcontrollers possess at least 128 bytes of internal Data Memory. Microcontrollers which possess internal Program Memory can execute instructions either from it or from external memory components. In contrast to a general purpose microprocessor, the 8051 microcontroller integrates peripheral devices and they need control and status registers. Logically, all microcontroller's registers, general purpose and related to embedded peripherals, are placed in a common group. The microcontroller subsystem which converts the parallel data into a serial bit stream and vice versa is called a serial port. The serial port is alternatively labelled Universal Asynchronous Receiver Transmitter.
