Memory Organization of 8051 Microcontroller 8051 micro-controller is based on the Harvard architecture, which supports separate program memory and separate data memory. The following paragraph explains the memory supported by 8051. Program Memory 8051 supports 4 KByte internal and 60 KByte external i.e. a total of 64 KByte of program memory. Selection of Program memory 8051 has an external access (EA) for selection of internal or external program memory. When EA=1; internal 4 KByte ROM is first fetched, control automatically transfers to external ROM once internal program memory limit is exceeded. When EA=0; Only the external program memory is accessible. So, the internal program memory is bypassed. Figure 6.1 shows the program memory of 8051   Internal Data Memory 8051 has 256 byte internal data memory of this the

Internal Architecture 8051 Microcontroller: The 8051 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of in-system programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard 8051 instruction set and pinout. The initial version of 8051 used 4 KByte ROM whereas later version employed on-chip flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the 8051 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications. The 8051 provides the following standard features: 4K bytes of ROM 128 bytes of RAM 4 i/o ports

Features of Microcontrollers : Microcontrollers are the system-on-chip devices, where emphasis is on reducing the chip count in the system as a whole. The number of features has been integrated inside it, and is described below: Clocking: They have an internal clocking circuit that allows easy interfacing of an external crystal with few capacitors or with an external clock input. They may also have an internal ring oscillator allowing it to run from the internally generated clock input. These clock inputs are used to synchronize the internal operations and to help in sequencing the execution of instructions as an an instruction cycle require a specific number of states or clock inputs. Internally, 8051 generates a two phase clock requiring the microcontroller six ‘T’