The 8051 Microcontroller Architecture A microcontroller (μC) is a single integrated circuit that executes a user program for controlling some device. A microcontroller has a CPU in addition to a fixed amount of RAM, ROM, I/O ports, serial port, and a timer all on a single chip. An embedded system uses a microcontroller to do one task and one task only. Microcontrollers are found in devices such as microwave ovens, automobiles, keyboards, CD players, cell phones, security systems, electronic toys, garage door openers, answering machines, … etc.

Differences between Microprocessors and Microcontrollers Microprocessors contain no ROM, no RAM, no I/O ports, while microcontrollers contain ROM, RAM, I/O ports, timers and other peripherals. Microcontroller systems are cheaper and more cost effective. The computing power of microprocessors is higher.

Factors Influencing the Selection of Microcontroller Chips Speed Packaging Power consumption Amount of RAM and ROM on-chip Number of I/O pins How easy to upgrade to higher performance versions Cost per unit

Commercial 8-bit Microcontrollers Intel’s 8051 Family Microchip’s PIC Family Motorola’s 6811 Family Zilog’s Z8 Family 8051 Family Manufacturers Intel (Original) Atmel Philips/Signetics AMD Infenion (Formally Siemens) Dallas Semiconductors

The 8051 Microcontroller 8-bit CPU 128B on-chip RAM 4KB on-chip ROM 2 Timers Four I/O Ports (Each 8-bits wide) One Serial Port DIP Package SMD Package

8051 Pin Configuration

8051 Family Members Timers On-chip RAM On-chip ROM Microcontroller 2 128 bytes 4K ROM 8051 8031 4K EPROM 8751 4K Flash ROM 8951 3 256 bytes 8K ROM 8052 8032 8K EPROM 8752 8K Flash ROM 8952

8051 IC Minimum Connections 1 Machine Cycle = 12 Clock Periods = 12/ fck fck = Clock frequency (4MHz – 30MHz)

8051 Memory Architecture The 8051 microcontroller uses the Harvard Architecture In Harvard Model the program memory is separated from data memory

Memory Organization Internal and External Memories Internal RAM Memory Map On-chip ROM Address Space

Code Memory

Memory Expansion

Special Function Registers (SFRs)

The 8051 Basic Registers

PSW Register (Flag Register)

8051 I/O Ports The 8051 contains 4 I/O Ports Each port has 8-lines Each port can be programmed for input or output of data Port 0 and Port 2 can be used data and address lines for external memory interfacing Port 3 has alternate functions for external connections Port 0 should be connected to pull-up resistors before using it for data input or output Port 1 is solely designed for I/O data exchange