The document discusses the 8051 microcontroller. It provides details about: - The 8051 microcontroller was developed by Intel in 1980 and was very popular due to features like serial communication, timers, interrupts, and RISC architecture. - The 8051 has features like an 8-bit ALU, 8-bit accumulator, 128 bytes of RAM, 4KB of ROM, four 8-bit I/O ports, two 16-bit timers/counters, and UART serial communication. - The pin configuration of the 8051 microcontroller depends on the package but commonly uses a 40-pin DIP package. The pin functions include the I/O and memory ports as well as power

1. 8051
Microcontroller
Dr. Tarun Chaudhary
Assistant Professor
ECE, NIT Jalandhar

2. The Microcontroller
• A microcontroller is a compact integrated circuit designed to govern a specific
operation in embedded system.
• An Embedded system is a combination of a computer hardware and software designed
for a specific function or functions. E.g. Mobile phone, AC, washing machine,
microwave oven, ATM machine, medical devices and vending machines etc…
• Microcontrollers can be considered as self-contained systems with a processor,
memory and I/O ports.

3. • Technically called as Intel MCS-51 Architecture, the 8051-microcontroller series was
developed by Intel in the year 1980 and were very popular in the 80’s (still are popular).
• 8051 Microcontroller has many features like Serial Communication, Timers, Interrupts,
Harvard architecture and uses RISC.
• Even though 8051 Microcontroller might seem a little bit out of fashion, but it is one of the
best platforms to get started with Microcontrollers, Embedded Systems and Programming
(both C and Assembly).
• The AVR (Advanced virtual RISC) microcontroller developed by Atmel in 1996.
• Programmable interface controller (PIC) from Microchip Technology.
• Various licensed Advanced RISC Machines (ARM) microcontrollers.
• ARM7- The best in class Microcontroller for smartphone users.

4. Difference Between Microprocessor and Microcontroller
MICROPROCESSOR MICROCONTROLLER
Microprocessor assimilates the function of a central processing unit (CPU) on to a single
integrated circuit (IC).
Microcontroller can be considered as a small computer which has a processor and some
other components in order to make it a computer.
Microprocessors are mainly used in designing general purpose systems from small to
large and complex systems like super computers.
Microcontrollers are used in automatically controlled devices.
Microprocessors are basic components of personal computers. Microcontrollers are generally used in embedded systems
Computational capacity of microprocessor is very high. Hence can perform complex
tasks.
Less computational capacity when compared to microprocessors. Usually used for
simpler tasks.
A microprocessor based system can perform numerous tasks. A microcontroller based system can perform single or very few tasks.
Microprocessors have integrated Math Coprocessor. Complex mathematical
calculations which involve floating point can be performed with great ease.
Microcontrollers do not have math coprocessors. They use software to perform floating
point calculations which slows down the device.
Generally microprocessors are not used in real time systems as they are severely
dependent on several other components.
Microcontrollers are used to handle real time tasks as they are single programmed, self
sufficient and task oriented devices.
The main task of microprocessor is to perform the instruction cycle repeatedly. This
includes fetch, decode and execute.
In addition to performing the tasks of fetch, decode and execute, a microcontroller
also controls its environment based on the output of the instruction cycle.
In order to build or design a system (computer), a microprocessor has to be
connected externally to some other components like Memory (RAM and ROM) and
Input / Output ports.
The IC of a microcontroller has memory (both RAM and ROM) integrated on it along
with some other components like I / O devices and timers.
The overall cost of a system built using a microprocessor is high. This is because of the
requirement of external components.
Cost of a system built using a microcontroller is less as all the components are readily
available.
Generally power consumption and dissipation is high because of the external devices.
Hence it requires external cooling system.
Power consumption is less.

5. The clock frequency is very high usually in the order of Giga
Hertz.
Clock frequency is less usually in the order of Mega Hertz.
Instruction throughput is given higher priority than interrupt
latency.
In contrast, microcontrollers are designed to optimize
interrupt latency.
Have few bit manipulation instructions Bit manipulation is powerful and widely used feature in
microcontrollers. They have numerous bit manipulation
instructions.

6. Architecture
• Von Neuman and Harvard: These two architecture are based on
how memory is used in the system.
• RISC and CISC: The fundamental difference between the two is that
RISC has less number of instructions, with each one capable of
performing a single operation, while CISC has a large number of complex
instructions capable of carrying out multiple internal operations.
Von Neuman
Harvard

7. Features od 8051 Microcontroller
• 8051 Microcontroller Features
• 8 – Bit ALU: ALU or Arithmetic Logic Unit is the heart of a microcontroller. It performs arithmetic and
bitwise operation on binary numbers. The ALU in 8051 is an 8 – Bit ALU i.e. it can perform operations on 8 –
bit data.
• 8 – Bit Accumulator: The Accumulator is an important register associated with the ALU. The accumulator in
8051 is an 8 – bit register.
• RAM: 8051 Microcontroller has 128 Bytes of RAM which includes SFRs and Input / Output Port Registers.
• ROM: 8051 has 4 KB of on-chip ROM (Program Memory).
• I/O Ports: 8051 has four 8 – bit Input / Output Ports which are bit addressable and bidirectional.
• Timers / Counters: 8051 has two 16 – bit Timers / Counters.
• Serial Port: 8051 supports full duplex UART Communication.
• External Memory: 8051Microcontroller can access two 16 – bit address line at once: one each for RAM and
ROM. The total external memory that an 8051 Microcontroller can access for RAM and ROM is 64KB
(216 for each type).
• Additional Features: Interrupts, on-chip oscillator, Boolean Processor, Power Down Mode, etc.

8. Pin configuration
• 8051 Microcontroller is available in a variety of IC Packaging Types. The most popular and commonly
used 8051 Microcontroller Packaging is Dual in-line or DIP. It is often available as a 40 – pin PDIP or
Plastic DIP IC.
• The other common packaging type is 44 – Lead PLCC (Plastic Leaded Chip Carrier). It is a kind of
surface mount package.
• Another surface mount packaging for 8051 microcontroller is 44 – Lead TQFP (Thin Quad Flat
Package).
• 8051 Microcontroller is available in a variety of packages like 40 – pin DIP or 44 – lead PLCC and
TQFP.
• The pin orientation of an 8051 Microcontroller may change with the package but the Pin Configuration
is same

9. • The following image shows the
8051 Microcontroller Pin Diagram
with respect to a 40 – pin Dual In-
line Package (DIP). Since it is a 40
– pin DIP IC, each side contains 20
Pins.
• There are other packages of
8051also, like the 44 – Lead PLCC
and the 44 – Lead TQFP. The
following image shows the 8051
Microcontroller Pin Diagram for
these packages specifically.

10. 8051 Microcontroller
Pin Description
• The Pin Description or Pin Configuration of the 8051
Microcontroller will describe the functions of each pins of
the 8051 Microcontroller. Let us now see the pin
description.
• Pins 1 – 8 (PORT 1): Pins 1 to 8 are the PORT 1 Pins of
8051. PORT 1 Pins consists of 8 – bit bidirectional Input /
Output Port with internal pull – up resistors. In older 8051
Microcontrollers, PORT 1 doesn’t serve any additional
purpose but just 8 – bit I/O PORT.
• In some of the newer 8051 Microcontrollers, few PORT 1
Pins have dual functions. P1.0 and P1.1 act as Timer 1 and
Timer 2 Trigger Input respectively.
• P1.5, P1.6 and P1.7 act as In-System Programming Pins i.e.
MOSI, MISO and SCK respectively.

11. • Pin 9 (RST): Pin 9 is the Reset Input Pin. It
is an active HIGH Pin i.e. if the RST Pin is
HIGH for a minimum of two machine
cycles, the microcontroller will be reset.
During this time, the oscillator must be
running.
• Pins 10 – 17 (PORT 3): Pins 10 to 17 form
the PORT 3 pins of the 8051
Microcontroller. PORT 3 also acts as a
bidirectional Input / Output PORT with
internal pull-ups. Additionally, all the PORT
3 Pins have special functions. The following
table gives the details of the additional
functions of PORT 3 Pins.

12. • Pins 18 & 19: Pins 18 and 19 i.e. XTAL 2 and XTAL 1 are the pins for connecting
external oscillator. Generally, a Quartz Crystal Oscillator is connected here.
• Pin 20 (GND): Pin 20 is the Ground Pin of the 8051 Microcontroller. It represents
0V and is connected to the negative terminal (0V) of the Power Supply.
• Pins 21 – 28 (PORT 2): These are the PORT 2 Pins of the 8051 Microcontroller.
PORT 2 is also a Bidirectional Port i.e. all the PORT 2 pins act as Input or Output.
Additionally, when external memory is interfaced, PORT 2 pins act as the higher
order address byte. PORT 2 Pins have internal pull-ups.
• Pin 29 (PSEN): Pin 29 is the Program Store Enable Pin (PSEN). Using this pins,
external Program Memory can be read.
• Pin 30 (ALE/PROG): Pin 30 is the Address Latch Enable Pin. Using this Pins,
external address can be separated from data (as they are multiplexed by 8051).
• During Flash Programming, this pin acts as program pulse input (PROG).
• Pin 31 (EA/VPP): Pin 31 is the External Access Enable Pin i.e. allows external
Program Memory. Code from external program memory can be fetched only if this
pin is LOW. For normal operations, this pins is pulled HIGH.
• During Flash Programming, this Pin receives 12V Programming Enable Voltage
(VPP).

13. • Pins 32 – 39 (PORT 0): Pins 32 to 39 are PORT 0 Pins. They are also bidirectional Input / Output Pins
but without any internal pull-ups. Hence, we need external pull-ups in order to use PORT 0 pins as I/O
PORT.
• In addition to acting as I/O PORT, PORT 0 also acts as lower order address/data bus when external
memory is accessed.
• Pin 40 (VCC): Pin 40 is the power supply pin to which the supply voltage is given (+5V).

14. 8051 Microcontroller Basic Circuit
• Now that we have seen the 8051
Microcontroller Pin Diagram and
corresponding Pin Description, we will proceed
to the basic circuit or schematic of the 8051
Microcontroller. The following image shows
the basic circuit of the 8051 Microcontroller.

15. • This basic circuit of 8051 microcontroller is the minimal
interface required for it to work. The basic circuit includes a
Reset Circuit, the oscillator circuit and power supply. Let us
discuss a little bit deeper about this basic circuit of 8051
Microcontroller.
• First is the power supply. Pins 40 and 20 (VCC and GND) of
the 8051 Microcontroller are connected to +5V and GND
respectively.
• Next is the Reset Circuit. A logic HIGH (+5V) on Reset Pin for
a minimum of two machine cycles (24 clock cycles) will reset
the 8051 Microcontroller. The reset circuit of the 8051
Microcontroller consists of a capacitor, a resistor and a push
button and this type of reset circuit provides a Manual Reset
Option. If you remove the push button, then the reset circuit
becomes a Power-On Reset Circuit.

16. • The next part of the basic circuit of the 8051 Microcontroller is the Oscillator Circuit
or the Clock Circuit. A Quartz Crystal Oscillator is connected across XTAL1 and
XTAL2 pins i.e. Pins 19 and 18. The capacitors C1 and C2 can be selected in the
range of 20pF to 40pF.
• As mentioned in the 8051 Microcontroller Pin Description, PORTS 1, 2 and 3, all
have internal pull – ups and hence can be directly used as Bidirectional I/O Ports.
But, we need to add external Pull – ups for PORT 0 Pins in order to use it as an I/O
Port.
• Generally, a 1KΩ Resistor Pack of 8 Resistors is used as a Pull – up for the PORT 0
of the 8051 Microcontroller.

17. Architecture of Intel’s 8051 microcontroller
• Features
 8051 microcontroller is designed by Intel in 1981
 The data width is 8 bits
 Registers are 8 bits
 4kb of ROM storage and 128 bytes of RAM storage
 It consists of four parallel 8-bit ports, which are programmable as well as per the requirement.
 An on-chip crystal oscillator is integrated in the microcontroller having crystal frequency of
12MHz.

20. Bus:
• Bus is a group of wires which is used to transfer data.
• The buses comprise 8, 16 or more cables. There are two types of buses:
 Address Bus: Microcontroller 8051 consists of 16-bit address bus.
 Data Bus: Microcontroller 8051 comprise of 8 bit data bus. It is employed to cart data.

21. • Register A accumulator: It is an 8 bit register. It holds a source operand and receives the
result of the arithmetic instructions (Addition, Subtraction, Multiplication and Division).
• B registers: B register is used during multiply and divide operations which can be performed
only upon numbers stored in the A and B registers. All other instructions in the program can use
this register as a spare accumulator (A).
• 8-bit ALU:

22. • Data Memory
 Data memory is often called as RAM, which a type of
volatile memory. Program written into it will not be
retained when power is down or the system is reset.
 Data memory is used to store temporary data,
intermediate results.
• Program Memory
 It is usually implemented a ROM.
 Program written in to it will be retained even when the
power is down or the system is reset.
 The instructions are stored in the program memory.

23. Oscillator:
• An on-chip crystal oscillator is integrated in the
microcontroller having crystal frequency of 12
MHz.
• It provides time source for CPU (Central
Processing Unit).

24. Need of Ports