1

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.

2

Differences between Microprocessors and Microcontrollers

1. Microprocessors contain no ROM, no RAM, no I/O ports, while microcontrollers contain ROM, RAM, I/O ports, timers and other peripherals.

2. Microcontroller systems are cheaper and more cost effective.

3. The computing power of microprocessors is higher.

3

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

4

Commercial 8-bit Microcontrollers

1. Intel’s 8051 Family

2. Microchip’s PIC Family

3. Motorola’s 6811 Family

4. Zilog’s Z8 Family

8051 Family Manufacturers

• Intel (Original)

• Atmel

• Philips/Signetics

• AMD

• Infenion (Formally Siemens)

• Dallas Semiconductors

5

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 PackageSMD

Package

6

8051 Pin Configuration

7

8051 Family Members

MicrocontrollerOn-chip ROMOn-chip RAMTimers

80514K ROM128 bytes2

80310128 bytes2

87514K EPROM128 bytes2

89514K Flash ROM128 bytes2

80528K ROM256 bytes3

80320256 bytes3

87528K EPROM256 bytes3

89528K Flash ROM256 bytes3

8

8051 IC Minimum Connections

1 Machine Cycle = 12 Clock Periods = 12/ fck

fck = Clock frequency (4MHz – 30MHz)

9

8051 Memory Architecture

• The 8051 microcontroller uses the Harvard Architecture

• In Harvard Model the program memory is separated from data memory

10

Memory Organization

Internal RAM Memory Map

Internal and External Memories

On-chip ROM Address Space

11

Code Memory

12

Memory Expansion

13

Special Function Registers (SFRs)

14

The 8051 Basic Registers

15

PSW Register (Flag Register)

16

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