8051 Microcontroller

Sub: Fundamental of Microcontroller and Applications
UNIT: 1 Microcontroller
Prof. P.V.Thokal [ME- EPS]
Asst. Professor
Electrical Engineering Department
Sanjivani College of Engineering , Kopargaon

• Home
– Appliances, intercom, telephones, security systems, garage door
openers, answering machines, fax machines, home computers, TVs,
cable TV tuner, VCR, camcorder, remote controls, video games,
cellular phones, musical instruments, sewing machines, lighting
control, camera, pinball machines, microwave ovens, Washing
machines etc.
• Office
– Telephones, computers, security systems, fax machines, copier,
laser printers, color printers etc.
• Auto
– Engine control, Air bag, ABS, Power window, Button start
– instrumentation, security system, transmission control, music system,
climate control, keyless entry, paint shop robots, welding robots,
CNC ,VNC machines

Why do we need to learn
Microprocessors/controllers?
• The microprocessor is the core of computer
systems.
• Nowadays many communication, digital
entertainment, portable devices, are controlled
by them.
• A designer should know what types of
components he needs, ways to reduce
production costs and product reliable.

Different aspects of a microprocessor/
Microcontroller
Hardware : Interface to the real world
Software : order how to deal with inputs

The necessary tools for a
microprocessor/Microcontroller
 CPU: Central Processing Unit
 I/O: Input /Output
 Bus: Address bus & Data bus
 Memory: RAM & ROM
 Timer
 Interrupt
 Serial Port

CPU
General-
Purpose
Micro-
processor
RAM ROM I/O
Port
Timer
Serial
COM
Port
Data Bus
Address Bus
Microprocessors:
• CPU for Computers
• No RAM, ROM, I/O on CPU chip itself
• Example：Intel’s 8085, 8086
General-purpose microprocessor

RAM ROM
I/O
Port
Timer
Serial
COM
Port
Microcontroller
CPU
• A smaller computer
• On-chip RAM, ROM, I/O ports...
• Example：Motorola’s 6811, Intel’s 8051, PIC 16X, PIC 18X
A single chip
Microcontroller

Difference Microcontroller Vs Microprocessor
Sr.no
.
Microcontroller Microprocessor
1 Microcontroller having inbuilt
RAM or ROM and inbuilt timer.
Do not have inbuilt RAM or ROM
and timer.
2 Input and output ports are
available.
Input and output ports are not
available, requires extra device
like 8155
3 Inbuilt serial port. Do not have inbuilt serial port,
requires 8250 device.
4 Separate memory to store
program and data.
Program and data are stored in
same memory.
5 Many functions pins on the IC. Less multifunction pins on IC.
6 Boolean operation directly
possible.
Boolean operation is not
possible directly.
7 It takes few instructions to read
and write data from external
memory.
It take many instruction to read
and write data from external
memory.
8 Most of the micro controllers
have power saving modes like
idle mode and power saving
mode. This helps to reduce
power consumption even further.
Most of the microprocessors do
not have power saving features
9 Used mainly in washing machine,
MP3 players
Mainly used in personal
computers
10 Micro controllers are based on
Harvard architecture where
program memory and Data
memory are separate
Microprocessors are based on
Von Neumann
model/architecture where
program and data are stored in
same memory module
11 Since external components are
low, total power consumption is
less and can be used with
devices running on stored power
like batteries.
Due to external components, the
entire power consumption is
high. Hence it is not suitable to
used with devices running on
stored power like batteries.

1. Meeting the computing needs of the task
efficiently and cost effectively
speed, the amount of ROM and RAM, the number of I/O
ports and timers, size, packaging, power consumption
easy to upgrade
cost per unit
2. Availability of software development tools
assemblers, debuggers, C compilers, emulator, simulator,
technical support
3. Wide availability and reliable sources of the
microcontrollers.
Three criteria in Choosing a
Microcontroller

Block Diagram of Microcontroller
CPU
On-chip
RAM
On-chip
ROM for
program
code
4 I/O Ports
Timer 1
Serial
PortOSC
Interrupt
Control
External interrupts
Timer 0
Timer/Counter
Bus
Control
TxD RxDP0 P1 P2 P3
Address/Data
Counter
Inputs

Architecture of 8051 microcontroller
P0 - - - - P7

Pins of 8051（1/4）
• Vcc（pin 40）：
-Vcc provides supply voltage to the chip.
-The voltage source is +5V.
• GND（pin 20）：ground
• XTAL1 and XTAL2（pins 19,18）

Figure (a). XTAL Connection to 8051
C2
30pF
C1
30pF
XTAL2
XTAL1
GND
 Using a quartz crystal oscillator
 We can observe the frequency on the XTAL2 pin.

Pins of 8051（2/4）
• RST（pin 9）：reset
–It is an input pin and is active high
（normally low）.
• The high pulse must be high at least 2
machine cycles.
– It is a power-on reset.
• Upon applying a high pulse to RST, the
microcontroller will reset and all values in
registers will be lost.
• Reset values of some 8051 registers

Pins of 8051（3/4）
 /EA（pin 31）：external access. It can’t be left
unconnected
– There is no on-chip ROM in 8031 and 8032 .
– The /EA pin is connected to GND to indicate the code
is stored externally.
– /PSEN ＆ ALE are used for external ROM.
– For 8051, /EA pin is connected to Vcc.
– “/” means active low.
 /PSEN（pin 29）：program store enable
– Reads the external program memory. This is an output
pin and is connected to the OE pin of the ROM.

Pins of 8051（4/4）
ALE（pin 30）：Address Latch Enable
–It is an output pin and is active high.
–8051 port 0 provides both address and
data.
• I/O port pins
–The four ports P0, P1, P2, and P3.
–Each port uses 8 pins.

RAM memory space allocation in the 8051
7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H
Register Bank 0
(Stack) Register Bank
1
Register Bank 2
Register Bank 3
Bit-Addressable RAM
(16 bytes)
Scratch pad RAM
(80 bytes)

Stack in the 8051
• The register used to access
the stack is called SP (stack
pointer) register.
• The stack pointer in the 8051
is only 8 bits wide, which
means that it can take value
00 to FFH. When 8051
powered up, the SP register
contains value 07.
7FH
30H
2FH
20H
1FH
17H
10H
0FH
07H
08H
18H
00H
Register Bank 0
(Stack) Register Bank
1
Register Bank 2
Register Bank 3
Bit-Addressable RAM
Scratch pad RAM

Registers
A
B
R0
R1
R3
R4
R2
R5
R7
R6
DPH DPL
PC
DPTR
PC
Some 16-bit Registers
Some 8-bit
Registers of the
8051

RESET Value of Some 8051 Registers
0000DPTR
0007SP
0000PSW
0000B
0000ACC
0000PC
Reset ValueRegister
RAM are all zero.

Pins of I/O Port
The 8051 has four I/O ports
– Port 0 （pins 32-39）：P0（P0.0～P0.7）
– Port 1（pins 1-8）：P1（P1.0～P1.7）
– Port 2（pins 21-28）：P2（P2.0～P2.7）
– Port 3（pins 10-17）：P3（P3.0～P3.7）
– Each port has 8 pins.
• Named P0.X （X=0,1,...,7）, P1.X, P2.X, P3.X
• Ex：P0.0 is the bit 0（LSB）of P0
• Ex：P0.7 is the bit 7（MSB）of P0
• These 8 bits form a byte.
Each port can be used as input or output (bi-direction).

Special Function Registers (SFR'S)
There are 21 Special function registers (SFR)
in 8051 microcontroller and this includes
Register A, Register B, Program Status Word
(PSW), PCON etc. There are 21 unique
locations for these 21 special function
registers and each of these register is of 1
byte size. Some of these special function
registers are bit addressable (which means
you can access 8 individual bits inside a
single byte), while some others are only byte
addressable.

Stack Pointer
 Stack pointer is an 8 bit register, the direct
address of SP is 81H and it is only byte
addressable, which means you cant
access individual bits of stack pointer.
 Usually after a system reset SP is
initialized as 07H and data can be stored
to stack from 08H onwards. This is usually
a default case and programmer can
alter values of SP to suit his needs.

Power Management Register (PCON)

Program Status Word (PSW)

Program Status Word (PSW) Continued....

Hardware Structure of I/O Pin
• Each pin of I/O ports
– Internal CPU bus：communicate with CPU
– D latch store the value of this pin
• D latch is controlled by “Write to latch”
– Write to latch＝1：write data into the D latch
– 2 Tri-state buffer：
• TB1: controlled by “Read pin”
– Read pin＝1：really read the data present at the pin
• TB2: controlled by “Read latch”
– Read latch＝1：read value from internal latch
– A transistor M1 gate
• Gate=0: open
• Gate=1: close

A Pin of Port 1
8051 IC
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P1.X
pinP1.X
TB1
TB2

Writing “1” to Output Pin P1.X
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P1.X
pinP1.X
2. output pin is
Vcc1. write a 1 to the pin
1
0 output 1
TB1
TB2

Writing “0” to Output Pin P1.X
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P1.X
pinP1.X
2. output pin is
ground1. write a 0 to the pin
0
1 output 0
TB1
TB2

Reading “High” at Input Pin
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU bus
M1
P1.X pin
P1.X
8051 IC
2. MOV A,P1
external pin=High
1. write a 1 to the pin MOV
P1,#0FFH
1
0
3. Read pin=1 Read latch=0
1
TB1
TB2

Reading “Low” at Input Pin
D Q
Clk Q
Vcc
Load(L1)
Read latch
Read pin
Write to latch
Internal CPU bus
M1
P1.X pin
P1.X
8051 IC
2. MOV A,P1
external pin=Low1. write a 1 to the pin
MOV P1,#0FFH
1
0
3. Read pin=1 Read latch=0
0
TB1
TB2

Other Pins
• P1, P2, and P3 have internal pull-up resisters.
– P1, P2, and P3 are not open drain.
• P0 has no internal pull-up resistors and does not
connects to Vcc inside the 8051.
– P0 is open drain(used in MOS)
• However, for a programmer, it is the same to
program P0, P1, P2 and P3.
• All the ports upon RESET are configured as
output.

A Pin of Port 0
8051 IC
D Q
Clk Q
Read latch
Read pin
Write to latch
Internal CPU
bus
M1
P0.X
pinP0.X
TB1
TB2
1. write a 1 to the pin
1
0
Output pin
floating

Port 0 with Pull-Up Resistors
P0.0
P0.1
P0.2
P0.3
P0.4
P0.5
P0.6
P0.7
Vcc
10 K
Port0

Addressing Modes
 Addressing modes specifies where the
data (operand) is. They specify the
source or destination of data (operand)
in several different ways, depending
upon the situation.
 Addressing modes are used to know
where the operand located is.

 There are 5 types of addressing modes:
1. Register (direct) addressing.
2. Direct addressing.
3. Register indirect addressing.
4. Immediate addressing.
5. Index addressing.

1.Register (Direct) Addressing Mode
 In register addressing mode; the source and/or
destination is a register.
 In this case; data is placed in any of the 8
registers(R0-R7); in instructions it is specified with
letter Rn (where ‘n’ indicates 0 to 7).
 For example;
1.MOV A, Rn (This is general instruction).
2.ADD A, R5 (This instruction will add the contents
of register R5 with the accumulator contents).

2.Direct Addressing Mode
 In direct addressing mode; the address of memory
location containing data to be read is specified in
instruction.
 In this case; address of the data is given with the
instruction itself.
 E.g.: MOV A, 25H (This instruction will read/move
the data from internal RAM address 25H and store
it in the accumulator.
25H (address) 1F To ACC. (A)

3.Register Indirect Addressing Mode
 In register indirect addressing mode; the
contents of the designated register are used
as a pointer to memory.
 In this case; data is placed in memory, but
address of memory location is not given
directly with instruction
 e.g.: MOV A,@R0 This instruction moves
the data from the register whose address is
in the R0 register into the accumulator.
R0 20H(address) 2F To ACC.(A)

4.Immediate Addressing Mode
 In immediate addressing mode, the data is
given with the instruction itself.
 In this case; the data to be stored in memory
immediately follows the opcode.
 e.g.: MOV A, #25H (This instruction will
move the data 25H to accumulator.
 ‘#’ means immediate
25H To ACC (A)

5.Index Addressing Mode
 Offset (from accumulator) is added to the base
index register( DPTR OR Program Counter) to
form the effective address of the memory location.
 In this case; this mode is made for reading tables
in the program memory.
 For example;
MOVC A, @ A + DPTR ( This instruction moves
the data from the memory to accumulator; whose
address is computed by adding the contents of
accumulator and DPTR)

Data Transfer Instructions
Mnemonic Description Byte
• MOV A, Rn Move register to accumulator 1
• MOV A, direct Move direct byte to acc. 2
• MOV A, @Ri Move indirect RAM to acc. 1
• MOV A, #data Move immediate data to acc. 2
• MOV Rn, A Move acc. to register 1
• MOV Rn, direct Move direct byte to register 2
• MOV Rn, #data Move immediate data to acc. 2
• MOV direct, A Move acc. to direct byte 2
• MOV direct, Rn Move register to direct byte 2

 MOV direct, direct Move direct byte to direct 3
 MOV direct, @ Ri Move direct RAM to direct byte 2
 MOV direct, # data Move immediate data to direct byte 3
 MOV @ Ri, A Move Acc. to indirect RAM 1
 MOV @ Ri, direct Move direct byte to indirect RAM 2
 MOV @ Ri, #data Move immediate data to indirect RAM 2
 MOV DPTR, #data Move immediate data to DPTR 3
 MOVC A @ A+DPTR Move code byte relative to DPTR to acc. 1
 MOVC A@ A+PC Move code byte relative to PC to acc. 1

 MOVX A,@ Ri Move external RAM to acc. 8 bit 1
 MOVX A, @ DPTR Move external RAM to acc 16 bit 1
 MOVX @Ri, A Move acc. to external RAM 8 bit 1
 MOVX @DPTR, A Move acc. to external RAM 16 bit 1
 PUSH direct Push direct byte onto stack 2
 POP direct Pop direct byte from stack 2
 XCH A, Rn Exchange register with acc. 1
 XCH A, direct Exchange direct byte with acc.2
 XCH A, @Ri Exchange indirect RAM with acc. 1

Arithmetic Instructions
 ADD A, Rn Add register to acc. 1
 ADD A, direct Add direct byte to acc. 2
 ADD A, @ Ri Add indirect RAM to acc. 1
 ADD A, # data Add immediate data to acc. 2
 ADDC A, Rn Add register to acc with carry 1
 ADDC A , direct Add direct byte to acc with carry 2
 ADDC A, @ Ri Add indirect RAM to acc with carry 1
 ADDC A, # data Add immediate data to acc with carry 2
 SUBB A, Rn Subtract register from acc with borrow 1

 SUBB A, direct Subtract direct byte from acc with borrow 2
 SUBB A, @ Ri Subtract Indirect RAM from acc with borrow 1
 SUBB A, # data Subtract immediate data from acc with borrow 2
 INC A Increment accumulator 1
 INC Rn Increment register 1
 INC direct Increment direct byte 2
 INC @ Ri Increment indirect RAM 1
 DEC A Decrement acc. 1
 DEC Rn Decrement register 1
 DEC direct Decrement direct byte 2
 DEC @ Ri Decrement indirect RAM 1
 INC DPTR Decrement data pointer 1
 MUL AB Multiply A and B 1
 DIV AB Divide A by B 1

Logical Instructions
 ANL A, Rn AND register to acc 1
 ANL A, direct AND direct byte to acc 2
 ANL A,@ Ri AND indirect RAM to acc 1
 ANL A, # data AND immediate data to acc 2
 ANL direct, A AND acc to direct byte 2
 ANL direct,# data AND immediate data to direct byte 3
 ORL A, Rn OR register to acc 1
 ORL A, direct OR direct byte to acc 2
 ORL A, @ Ri OR indirect RAM to acc 1
 ORL A, # data OR immediate data to acc 2
 ORL direct, A OR acc to direct byte 2
 ORL direct, #data OR immediate data to direct byte 3

 XRL A, Rn EX-OR register to acc 1
 XORL A, direct EX-OR direct byte to acc 2
 XORL A,@ Ri EX-OR indirect RAM to acc 1
 XORL A, # data EX-OR immediate data to acc 2
 XORL direct, A EX-OR acc to direct byte 2
 XORL direct, # data EX-OR immediate data to direct byte 3
 CLR A Clear accumulator 1
 CPL A Complement accumulator 1
 SWAP A Swap nibble within acc 1
 RL A Rotate acc left 1
 RLC A Rotate acc left through carry 1
 RR A Rotate acc right 1
 RRC A Rotate acc right through carry 1

Logical Instructions On Bits
 CLR C Clear carry 1
 CLR bit Clear direct bit 2
 SETB C Set carry 1
 SETB bit Set direct bit 2
 CPL C Complement carry 1
 CPL bit Complement direct bit 2
 ANL C, bit AND direct bit to carry 2
 ANL C,/bit AND complement of direct bit to carry 2
 ORL C, bit OR direct bit to carry 2
 ORL C,/bit OR complement direct to bit to carry 2
 MOV C, bit Move direct bit to carry 2
 MOV bit, C Move carry to direct bit 2

MOV instruction
 MOV destination, source ; copy source to destination
 MOV instruction copies data from one location to another.
This instruction tells the CPU to copy the source operand
to the destination operand.
 “MOV A, R0” copies the contents of register R0 to acc.
 After this instruction is executed, register A will have the
same value as register R0.
MOV A, #55H ; Load value 55H into register A
(A=55H)
MOV R0, A ; copy contents of A into R0
(A=R0=55H)

ADD instruction
• ADD A, source ; ADD the source operand to
acc
MOV A, #20H ; load 20H into A
MOV R0, #30H ; load 30H into R0
ADD A, R0 ; add R0 to acc
; (A=A+R0)
OR
MOV A, #20H ; Load one operand into A
ADD A, #30H ; add the second operand 30H to
A

Some important terms
 Machine language: “A program consists of
0s and 1s is called as machine language”
 Assembly language programs must be
translated into machine code by a program
called an “assembler”
 Assembly language is referred to as a “Low-
level language”, it deals directly with the
internal structure of CPU.
 To program in Assembly language, the
programmer must know all the registers of
the CPU and size of each, also other details.

• C, C++, Java and numerous other languages
are called “High-level languages” because
the programmer does not have to be
concerned with internal details of CPU.
• “Assembler” is used to translate an
Assembly language program into machine
code(sometimes also called object code or
opcode or operation code)
• “High level languages are translated into
machine code by a program called a
compiler”.

Steps to create a program
Myfile.lst
EDITOR
PROGRAM
ASSEMBLER
PROGRAM
LINKER
PROGRAM
OH
PROGRAM
Myfile.asm
Other .obj
fileMyfile.obj
Myfile.abs
Myfile.hex

Unconditional Jump Instructions
 All conditional jumps are short jumps
– Target address within -128 to +127 of PC
 LJMP (long jump): 3-byte instruction
– 2-byte target address: 0000 to FFFFH
– Original 8051 has only 4KB on-chip ROM
 SJMP (short jump): 2-byte instruction
– 1-byte relative address: -128 to +127

Call Instructions
 LCALL (long call): 3-byte instruction
– 2-byte address
– Target address within 64K-byte range
 ACALL (absolute call): 2-byte instruction
– 11-bit address
– Target address within 2K-byte range

Basics of Serial Communication
• Computers transfer data in two ways:
– Parallel: Often 8 or more lines (wire conductors) are
used to transfer data to a device that is only a few feet
away.
– Serial: To transfer to a device located many meters away,
the serial method is used. The data is sent one bit at a
time.

Serial data communication
 Serial data communication uses two methods
– Asynchronous method
– Synchronous method
 There are special IC’s made by many
manufacturers for serial communications.
– UART (universal asynchronous Receiver
transmitter)
– USART (universal synchronous-asynchronous
Receiver-transmitter)

Asynchronous – Start & Stop Bit
 Asynchronous serial data communication is
widely used for character-oriented transmissions
– Each character is placed in between start and
stop bits, this is called framing.
– Block-oriented data transfers use the
synchronous method.
 The start bit is always one bit, but the stop bit can
be one or two bits
 The start bit is always a 0 (low) and the stop bit(s)
is 1 (high)

Asynchronous – Start & Stop Bit
41H

Data Transfer Rate
The rate of data transfer in serial data
communication is stated in bps (bits per second).
Another widely used terminology for bps is baud
rate.
– It is modem terminology and is defined as the number of
signal changes per second
– In modems, there are occasions when a single change
of signal transfers several bits of data
As far as the conductor wire is concerned, the baud
rate and bps are the same.

Machine cycle calculation
 1 machine cycle = 12 clock cycles

MAX232 (Serial interface with PC)

Baud Rate
• No. of signal changes per second is
called as Baud Rate
• The rate of data transfer in serial data
communication is stated in BPS(Bits Per
Second)
• As far as conductor wire is concerned,
the baud rate and bps are the same
• The 8051’s serial communication UART
circuitry divides the machine cycle
frequency of 921.6 KHz by 32 gives
28800Hz.

SCON (Serial control) register

SBUF Register
 Serial Buffer is an 8 bit register.
 For a byte (8 bit) of data to be transferred
via the TXD line, it must be placed in the
serial buffer register.
 Similarly SBUF register holds the byte of
data when it is received by the 8051’s RXD
line.

Operating Modes
SM0 SM1 Trans. format Baud Rate
0 0 Serial Mode 0, , 8 bits 1/12
* 0 1 Serial Mode 1,8 bit data, variable
1 stop bit, 1 start bit(10bits)
1 0 Serial Mode 2 1/32 or 1/64
11 bits(1 start, 1 stop, 8 bit data, 9th bit programmble)
1 1 Serial Mode 3 variable
11 bits(1 start, 1 stop, 8 bit data, 9th bit programmble)

Steps to write a program
1) Load TMOD register with the value 20H, indicating the use of
timer 1,mode 2
(8 bit auto - reload) to set the baud rate.
2) Then TH1 is loaded with one of the values shown in Table 10-4
3) SCON is loaded with value 50 H, indicating serial mode 1.
4) TR1 is set to 1 to start timer 1
5) Charact. To be transferred is written into SBUF
6) TI is flag is monitored with the use of the information
“JNB TI ,xx”
7) TI is cleared by “CLR TI” instruction
8) Keep sending “A”

Programming the 8051 to transfer data
serially

Baud rates for SMOD=0
Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz
and
921.6 kHz / 32 = 28,800 Hz since SMOD = 0

Doubling the baud rate in the 8051
 By Doubling the crystal frequency
 By making SMOD= 1 of PCON register

Timer/Counter
8051 has two timers/Counters. They can be
used either as Timer to generate time delay. Or
as Counter to Count Events outside
microcontroller.
Timer 0 (T0) : 16 bit wide TH0(8) TL0(8)
Timer 1 (T1): 16 bit wide TH1(8) TL1(8)

Mode 1 programming
1.Loaded value into TL and TH
2.”SETB TR0” for timer 0 ;”SETB TR1” for timer 1
3.If TF (timer flag) = high “CLR TR0” or “CLR TR1”
4.Reloaded TH and TL value, TF reset to 0

References
Sr.
No.
Title of Book Authors Publication House
1 “8051Microcontroller” Scott Mackenzie Pearson Education.
2 “8051 microcontroller” Subrata Ghoshal, Pearsons Publishers.
3
“Microprocessor and
Microcontroller”
Theagrajan BS Publication
Text books :
Sr. No. Title of Book Authors Publication House
1
“The 8051 Microcontroller and
Embedded Systems”
Muhammad Ali Mazidi, J.G.
Mazidi
Pearsons Publishers
2
“8051 Microcontroller, Hardware,
software and applications”
V Udayashankara and M S
MallikarjunaSwamy
TATA McGraw Hill
3 “Microcontroller 8051” Ajay Deshmukh TATA McGraw Hill.
4
“The 8051 Microcontrollers-
Architecture, Programming and
Applications”
K. J. Ayala
Peram International
Publications
Reference books:

8051 Microcontroller

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