1. 8051 Microcontroller Features and its Applications
By:
Prof. Rajiv R Bhandari

2. CONTENTS Microcontrollers Applications Of Microcontrollers
Microprocessor Vs Microcontrollers
History Of 8051 Microcontroller
Features Of Microcontroller
Block Diagram And Pin Description Of 8051
Registers
Memory Mapping In 8051
Timers And Counters
Serial Communication
Interrupts
Applications Of Microcontroller

3. Microcontrollers A single chip
Microcontrollers are small computing systems on a single chip.
A microcontroller will also be referred to as an MCU.
Central Processing Unit (CPU)
Program memory
Random Access Memory (RAM)
EEPROM - Electrically Erasable Programmable Read Only Memory
USARTs, Timer/Counters, ADC, DAC, I/O Ports, CANs, SPIs, etc.
Examples : Motorola’s 6811,Intel’s 8051,Zilog’s Z8 and PIC 16X.
CPU
RAM
ROM
A single chip
Serial
Port
I/O Port
Timer

4. Applications Of Microcontrollers
Cell phone
Pager
Watch
Calculator
Video Games
Alarm clock
Air Conditioner
TV remote
Microwave Oven
Washing Machines
An Electronic Smart Weight Display System
Robotic System
An Anti-Lock Braking System Monitor

6. Applications cont’d

7. Microprocessor vs Microcontroller
CPU is stand-alone, RAM,
ROM, I/O, timer are separate
Designer can decide on the
amount of ROM, RAM and
I/O ports.
Expansive
Versatility
General-purpose
Microcontroller
CPU, RAM, ROM, I/O and
timer are all on a single
chip
Fix amount of on-chip
ROM, RAM, I/O ports
Highly bit addressable
For applications in which cost, power and space are Critical
Single-purpose

8. History of 8051 Microcontroller
In the year Intel corporation introduced an 8 bit
microcontroller called 8051.
It has 4K bytes of ROM,128 Bytes of RAM , a serial port, two 16-bit Timers and 32 I/O pins.
CPU can work with 8 bit of data at a time.
Data larger than 8 bit can be broken into 8 bit pieces to be
processed by the CPU

9. Important Features of 8051 4K bytes ROM 128 bytes RAM
Four 8-bit I/O ports
Two 8/16 bit timers
Serial port
64K external code memory space
64K data memory space
Multiple internal and external interrupt sources

10. Architecture of 8051 Microcontroller
Oscillator and timing
4096 Bytes Program Memory
(ROM)
128 Bytes
Data Memory
(RAM)
Two 16 Bit Timer/Event Counters
Internal data bus
8051 CPU
Programmable I/O
Programmable Serial Port Full Duplex UART Synchronous Shifter
64 K Byte Bus Expansion Control
subsystem interrupts
Parallel ports
Address Data Bus
I/O pins
Control
Serial Output
External interrupts
Serial Input

11. 8051 CPU Registers A (8-bit Accumulator)
B (8-bit register for Mul &Div)
PSW (8-bit Program Status Word)
SP (8-bit Stack Pointer)
PC (16-bit Program Counter)
DPTR (16-bit Data Pointer)

12. Flag Register
Flags are 1-bit registers provided to store the results of certain program instructions
Other instructions can test the condition of the flags and make decisions based on the flag states
Flags are grouped inside the Program Status Word (PSW) and the Power Control (PCON) registers for convenient addressing
Math Flags: respond automatically to the outcomes of math operations (CY, AC, OV, P)
PSW contains the register select bits (RS1, RS0) that identify which of the four general-purpose register banks is currently in use by the program

13. 7 6 5 4 3 2 1 CY AC F0 RS1 RS0 OV -- P Bit Symbol Function 7 CYCY AC F0
RS1
RS0 OV -- P
Bit
Symbol
Function 7 CY
Carry Flag; used in arithmetic, JUMP, ROTATE, and BOOLEAN instruction 6 AC
Auxiliary carry flag; used for BCD arithmetic 5 F0
User flag 0 4
RS1
Register bank select bit 1 3
RS0
Register bank select bit 0 2 OV
Overflow flag; used in arithmetic instructions 1 --
Reserved for future use P
Parity flag; shows parity of register A: 1 = Odd Parity

14. Pin Description of 8051 The 8051 is a 40 pin
device, but out of these 40 pins, 32 are
used for I/O.
24 of these are dual purpose, i.e. they can operate as I/O or a control line or as part of address or data bus.

15. List of registers

16. List of registers contd..

17. Internal Memory 8051 has internal RAM (128 bytes) and ROM (4Kbytes)
A functioning computer must have memory for program code bytes, commonly in ROM, and RAM memory for variable data that can be altered as the program runs
8051 has internal RAM (128 bytes) and ROM (4Kbytes)
8051 uses the same address but in different memories for code and data
Internal circuitry access the correct memory based on the nature of the operation in progress
Can add memory externally if needed

18. 8051 Internal RAM Organisation07 06 05 04 03 02 01 00 0F 0E 0D 0C 0B 0A 09 08 17 16 15 14 13 12 11 10 1F 1E 1D 1C 1B 1A 19 18
Bank 0
Bank 1
Bank 2
Bank 3 27 26 25 24 23 22 21 20 2F 2E 2D 2C 2B 2A 29 28 7F 6F 5F 4F 3F 2F 1F 0F 30 7F
Working Registers
Bit Addressable
General Purpose

19. Program Status Word (PSW)
Bank Select Bits, RS1, & RS0 to select 1 of 4 register bank

20. Special Function Registers (SFR)
8051 has 21 SFRs which occupy the addresses from 80H to FFH (128bytes)
Not all of the addresses from 80H to FFH are used for SFRs
Attempt to use the “empty” addresses may get unpredictable result

21. Special Function Register Map
Bit addressable

22. Value of SFR at Reset

23. Internal ROM
Internal ROM occupies the code address space from 0000H to 0FFFH (Size = 4K byte)
Program addresses higher than 0FFFH will automatically fetch code bytes from external program memory
Code bytes can also be fetched exclusively from an external memory by connecting the external access pin (EA) to ground

24. Timers /Counters The 8051 has 2 timers/counters: Timer/Counter 0
Used as a time delay generator.
Many microcontroller application requires the counting of external events such as frequency, time delay.

25. Registers Used in Timer/Counter
8051 has two 16-bit Timer registers ,Timer 0 & Timer 1.
As 8051 has 8-bit architecture , each Timer register is treated as two 8-bit registers namely TH0, TL0, TH1, TL1.
One 8-bit mode register -TMOD.
One 8-bit control register-TCON.

26. Timer Set the initial value of registers
Start the timer and then the 8051 counts up.
Input from internal system clock (machine cycle)
When the registers equal to 0 and the 8051 sets a bit to denote time out
8051 P2 P1 to
LCD
Set
Timer 0
TH0
TL0

27. Counter Count the number of events
Show the number of events on registers
External input from T0 input pin (P3.4) for Counter 0
External input from T1 input pin (P3.5) for Counter 1
External input from Tx input pin.
We use Tx to denote T0 or T1.
8051
TH0 P1 to
LCD
TL0
P3.4
a switch T0

28. TMOD Register GATE C/T M1 M0 Timer 1 Timer 0 (MSB) (LSB)
Both Timer 0 &Timer 1 use the Same Mode register TMOD.
It is an-8-bit register .
The lower 4-bits are meant for Timer 0 &the upper 4-bits are meant for Timer 1
It is used similar to any other register of

29. Set for counter operation (input from Tx input pin).
TMod contd….
C/T : Timer or counter selected cleared for timer operation (input from internal system clock).
Set for counter operation (input from Tx input pin).
M1,M0 : Used for mode selection. Because the Timers of 8051 can be set in 4-different modes.
M M Mode Operation
bit timer mode bit THx + 5-bit TLx
bit timer mode bit THx + 8-bit TLx
bit auto reload THx holds a value which is to be
reloaded into TLx each time it overflows.
Split timer mode

30. Gate Every timer has a mean of Starting and Stopping. GATE=0
Internal control
The start and stop of the timer are controlled by way of software.
GATE=1
External control
The hardware way of starting and stopping the timer by software and an external source.
Timer/counter is enabled only while the INT pin is high and the TR control pin is set (TR).

31. TCON Register
Timer control register TMOD is a 8-bit register which is bit addressable and in which Upper nibble is for timer/counter,
lower nibble is for interrupts

32. Tcon contd… TR (Timer run control bit)
TR0 for Timer/counter 0; TR1 for Timer/counter 1.
TR is set by programmer to turn timer/counter on/off.
TR=0 : off (stop)
TR=1 : on (start)
TF (timer flag, control flag)
TF0 for timer/counter 0; TF1 for timer/counter 1.
TF is like a carry. Originally, TF=0. When TH-TL roll over to 0000 from FFFFH, the TF is set to 1.
TF=0 : not reach
TF=1: reach
If we enable interrupt, TF=1 will trigger ISR.

33. 8051- SERIAL COMMUNICATION

34. RxD and TxD pins in the 8051
The 8051 has two pins for transferring and receiving data by
serial communication. These two pins are part of the
Port3(P3.0 &P3.1)
These pins are TTL compatible and hence they require a line
driver to make them RS232 compatible
Max232 chip is one such line driver in use.
Serial communication is controlled by an 8-bit register called
SCON register, it is a bit addressable register.

35. SCON (Serial control) register

36. SM0 , SM1
These two bits of SCON register determine the framing of data
by specifying the number of bits per character and start bit and stop bits.
There are 4 serial modes.
SM SM1
Serial Mode 0
Serial Mode 1, 8 bit data,
1 stop bit, 1 start bit
Serial Mode 2
Serial Mode 3

37. REN, TI, RI REN (Receive Enable) also referred as SCON.4.
When it is high, it allows the 8051 to receive data on the RxD pin. So to receive and transfer data REN must be set to 1.
When REN=0,the receiver is disabled.

38. TI,RI Contd… TI (Transmit interrupt)
It is the D1 bit of SCON register.
When 8051 finishes the transfer of 8-bit character, it raises the TI flag to indicate that it is ready to transfer another byte.
The TI bit is raised at the beginning of the stop bit.
RI (Receive interrupt)
It is the D0 bit of the SCON register.
When the 8051 receives data serially ,via RxD, it gets rid of the start and stop bits and places the byte in the SBUF register.
Then it raises the RI flag bit to indicate that a byte has been received and should be picked up before it is lost.
RI is raised halfway through the stop bit.

39. Interrupt Sources 8051 has 6 sources of interrupts Reset
Timer 0 overflow
Timer 1 overflow
External Interrupt 0
External Interrupt 1
Serial Port events (buffer full, buffer empty, etc)

40. Interrupt Enable Register
Upon reset all Interrupts are disabled and do not
respond to the Microcontroller
These interrupts must be enabled by software in
order for the Microcontroller to respond to them.
This is done by an 8-bit register called Interrupt
Enable Register (IE).

41. EA : Global enable/disable.
: Undefined.
ET2 : Enable Timer 2 interrupt.
ES : Enable Serial port interrupt.
ET1 : Enable Timer 1 interrupt.
EX1 : Enable External 1 interrupt.
ET0 : Enable Timer 0 interrupt.
EX0 : Enable External 0 interrupt.

42. Interrupt Priorities
If two interrupt sources interrupt at the same time ,the
interrupt with the highest PRIORITY gets serviced first.
All interrupts have a power on default priority order.
External interrupt 0 (INT0)
Timer interrupt0 (TF0)
External interrupt 1 (INT1)
Timer interrupt1 (TF1)
Serial communication (RI+TI)
Priority can also be set to “high” or “low” by IP reg.

43. Interrupt Priorities (IP) Register
---
PX0
PT0
PX1
PT1 PS
PT2
IP.7: reserved IP.6: reserved IP.5: Timer 2 interrupt priority bit (8052 only) IP.4: Serial port interrupt priority bit IP.3: Timer 1 interrupt priority bit IP.2: External interrupt 1 priority bit IP.1: Timer 0 interrupt priority bit IP.0: External interrupt 0 priority bit

44. Interrupt inside an interrupt
---
PX0
PT0
PX1
PT1 PS
PT2
A high-priority interrupt can interrupt a low-priority interrupt
All interrupt are latched internally
Low-priority interrupt wait until 8051 has finished servicing
the high-priority interrupt

45. Applications of 8051 microcontroller
Embedded system
Industrial
Computer networking
Power input to the 8051 is very simple and straight forward.
8051 could be used in low-power applications.

46. Applications cont’d
The 8051 has been in use in a wide number of devices, mainly because it is easy to integrate into a project or build a device around.
Energy Management:
Efficient metering systems help in controlling energy usage in homes and industrial applications.
These metering systems are made capable by incorporating microcontrollers.

47. Applications cont’d Touch screens: Automobiles:
A high number of microcontroller providers incorporate touch-sensing capabilities in their designs.
Portable electronics such as cell phones, media players and gaming devices are examples of microcontroller-based touch screens.
Automobiles:
The 8051 finds wide acceptance in providing automobile solutions.
They are widely used in hybrid vehicles to manage engine variants.
Functions such as cruise control and anti-brake system have been made more efficient with the use of microcontrollers.

48. Applications cont’d Medical Devices:
Portable medical devices such as blood pressure and glucose
monitors use microcontrollers will to display data, thus
providing higher reliability in providing medical results.

49. Thank you