final 8051 printout

7/27/2019 Final 8051 Printout

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IntroductionBlock Diagram and Pin Description of the 8051

Registers

Memory mapping in 8051

Stack in the 8051

I/O Port ProgrammingTimer

Serial Communication

Interrupt

Contents:


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CPU: Central Processing Unit

I/O: Input /Output

Bus: Address bus & Data bus

Memory: RAM & ROM

Timer

Interrupt

Serial Port

Parallel Port

Necessary tools for processor/controller


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Stand alone general purpose processors No RAM, ROM, I/O on CPU chip itself

ExampleIntels x86, Motorolas 680x0

Microprocessors & Microcontrollers

A smaller computer

On-chip RAM, ROM, I/O ports...

ExampleMotorolas 6811, Intels 8051,Zilogs Z8 and PIC 16X

Microprocessor

Microcontroller


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Microprocessor

CPU is stand-alone, RAM, ROM, I/O ,

timer have to be added externally.

designer can decide on the amount of

ROM, RAM and I/O ports.

general-purpose

ExampleIntels x86, Motorolas 680x0

Microcontroller

CPU, RAM, ROM, I/O and timer are all on a

single chip

fix amount of on-chip ROM, RAM, I/O ports

Single-purpose for applications in which cost,

power and space are critical

ExampleIntels 8051, Motorolas 6811,

Zilog Z80

Microprocessors vs Microcontrollers


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Complex instruction set computer

Large number of complex

instructions, take more clockcycles to execute.

Variable length instructions

hence difficult to implement

pipelining.

Supports memory to memory

addressing modes.

Software design is easy.

Ex:Intel 80X86,

Reduced instruction set computer

Instructions are few and simple,

majority of them are executed in asingle clock cycle

Majority of the instructions are of

same length and pipelining is

effectively achieved.

All operations are register-to-registers.

Load-Store architecture.

Software design is complex.

Programmers have to effectively

utilize the available instructions tocomplete the task.

Ex:ARM,Atmel Avr,Pic

The CISC approach attempts to minimize the number of instructions per program,sacrificing the number of cycles per instruction. RISC does the opposite, reducing thecycles per instruction at the cost of the number of instructions per program.

CISC vs RISC


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ROM(read only memory):Nonvolatile memory used to store the instructions.

PROM(Programmable ROM): Type of ROM memory which is programmed

after manufacturing.

EPROM(Erasable Programmable ROM):Once programmed , an EPROM can

be erased by exposing to UV-rays and can be reprogrammed.

EEPROM(Electrically Erasable Programmable ROM):EEPROM can be erasedand reprogrammed by applying the electrical voltage.

FLASH: It is a specific type of EEPROM memory that is erased and

reprogrammed in large blocks and is comparitively faster than EEPROM.

emory un : Memory is any physical device to store data.


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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 unit2. 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 chossing a Microcontroller


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8051 Basic Component

Feature 8031 8051 8052 8751 8951ROM NO 4kB 8kB 4kB UV Eprom 4KB FLASRAM (Bytes) 128 128 256 128 128TIMERS 2 2 3 2 2I/O PINS 32 32 32 32 32SERIAL PORTS 1 1 1 1 1

INTERRUPT 6 6 8 6 6SOURCES

8 bit controller

4KB of internal ROM and 128 bytes of RAM memory.

Four 8bit I/O ports(P0,P1,P2,P3). Two 16 timers/counters.

One serial port(UART).

8bit data bus and 16bit address bus hence can access 64k of

external memory. 6 Interrupts

8051 family of controllers

l k


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CPU

On-chip

RAM

On-chip

ROM for

program

code

4 I/O Ports

Timer 0

Serial

PortOSC

Interrupt

Control

External interrupts

Timer 1

Timer/Counter

Bus

Control

TxD RxDP0 P1 P2 P3

Address/Data

Counter

Inputs

Block Diagram


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8051 Block diagram

Pi Di f 8051


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Pin Diagram of 8051

Pi D i ti f 8051


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P0: Can be used as 8bit port or multiplexed lower 8bit data

and address bus.P1:Can be used as simple 8bit I/O port.

P2: Can be used as 8bit port or higher 8bit address bus.

P3:It is multifunctional port used as normal port or as special

port for serial communication, interrupts, timers and for

external read write signals.

VCCVcc provides supply voltage(+5v) to the chip.

GND

ground(0v)

XTAL1 & XTAL2: A quartz crystal

oscillator is connected accross XTAL1

&XTAL2, which provides the clock source for the controller.

Pin Description of 8051

Pi D i ti f 8051


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DPTR 0000

Reset ValueRegister

RAM are all zero.

RESET: It is an active high (normally low) input signal used to reset

the controller. Upon applying a high pulse to this pin the controller

will reset and starts the execution from first(from memory location0000h), this is often referred as power on reset(POR).

SP 07PSW 00

B 00

ACC 00PC 0000

Pin Description of 8051

Reset values of some 8051 Registers


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8051 IC

D Q

Clk Q

Vcc

Load(L1)

Readlatch

Read pin

Write to latch

Internal CPU

bus

M1

P1.X

pinP1.X

TB1

TB2

P0.x

A Pin of Port1

W itin 1 t O tp t Pin P1 x


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Writing 1 to Output Pin P1.x

Writing 0 to Output Pin P1.x

Reading high at Intput Pin P1 x


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Reading high at Intput Pin P1.x

Reading low at Intput Pin P1.x


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D Q

Clk Q

Read latch

Read pin

Write to latch

Internal CPUbus

M1

P0.X

pinP1.X

TB1

TB2

P0.0P0.1P0.2P0.3P0.4P0.5P0.6P0.7

DS5000

8751

8951

Vcc10 K

Port

0

A Pin of Port0

Port0 with Pull Up Resistors


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A

B

R0

R1

R3

R4

R2

R5

R7

R6

DPH DPL

PC

DPTR

Some 8051 16-bit RegisterSome 8-bit Registers of

the 8051

CY AC F0 RS1 RS0 OV _ P

PSW:Program Status Word

Programmers Model Of 8051


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ROM memory map in 8051

family

0000H

0FFFH

0000H

1FFFH

8751

AT89C518752

AT89C52

4k 8k

AtmelCorporation

7FH

30H

2FH

20H

1FH

17H10H

0FH

07H

08H

18H

00H

Register Bank 3

Bit-Addressable RAM

Scratch pad RAM

Register Bank 2

Register Bank 1

Register Bank 0

RAM memory map in

8051 family

Memory mapping of 8051

SFR(special function re isters


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SFR(special function registers

Stack of 8051


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Stack is a part of RAM used by CPU to store the information. This information could be dataor address. Usually it is used to store the return address in case of call instruction.

The register used to access the stack is called SP (stack pointer) .

The stack pointer in the 8051 is only 8 bits wide, which means that it can take value 00 toFFH. When 8051 powered up, the SP register contains value 07.

Instructions used to access the stack memory are PUSH & POP.

The storing of a CPU register in the stack is called a PUSH. SP is pointing to the last

used location of the stack(top of stack).As we push data onto the stack, the SP is

incremented by one.

Loading the contents of the stack back into a CPU register is called a POP. Withevery pop, the top byte of the stack is copied to the register specified by the

instruction and the stack pointer is decremented once

Stack of 8051

Programming Environment


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Programming Environment


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Different ways of accessing the data is known as addressing modes.

Immediate addressing mode: In this mode the data is provided

within the instruction itself.(#) indicates immediate mode.

Ex: mov a,#20h, add a,#30h

Register addressing mode: Here both the source and destination are

cpu registers.

Ex: mov a,r0 mov r0,a add a,r0.

Direct addressing mode: Here the data is stored in the memory

whose address will be provided in the instruction itself.

Ex: mov a, addr mov a,50h mov 40h,a

Indirect addressing mode: Here the data is stored in the memory

whose address will be stored in one of the cpu registers(R0,R1,DPTR)

Ex: mov a,@r0 mov @r1,a mov a,@dptr.

Here @ indicates indirect mode.

Addressing modes

8051 I t ti S t


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An assembly language instruction consist of four fields.

Label: mnemonic operands ;comment

Label: This field is used to refer a particular line of code, usually used inbranching and call instruction to jump to a particular label.

Mnemonic: Specifies the operation like add, mov, mul etc.

Operands: An entity on which the operation is performed. Here the

number of operands depends on the type of instruction.Comment:Used to document the program, these are written at the end of

the line following a semicolon(;) and are ignored by assembler.

8051 instructions are grouped into 5 groups

1)Data transfer instructions 2)Arithmetic instructions

3)Logical instructions 4)Branching instructions

5)Boolean instructions

8051 Instruction Set

D t t f i t ti


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Immediate mode

MovA, #dataMov B, #data

Mov Rn, #data

Mov DPTR, #data(16bit)

Direct modeMovA, addr

Mov addr, A

Mov Rn, addr

Mov addr, Rn

Register modeMovA, Rn

Mov Rn, A

Indirect mode

MovA, @RiMov @Ri, AMov @Ri, #dataMov @Ri, addr

Mov A, @DPTRMov @DPTR, AMovc A, @A+DPTRMovc A, @A+PC

Movx A, @DPTRMovx A, @RiMovx @DPTR, AMovx @Ri, A

Data transfer instructions

A ith ti i t ti


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Immediate modeADDA, #data

SUBB A, #data

ADDC A, #data

SUBB A, #data

Direct modeADDA, addr

SUBB A, addr

INC addr

DEC addr

Register modeADD A, B

ADD A, Rn

ADDC A, B

SUBB A, B

MUL AB

DIV AB

INC A

INC Rn (n=0-7)

DEC

Indirect modeADDA, @Ri

ADD A, @DPTR

ADDCA, @RiINC @Rn (n=0 or 1)

DEC @Rn

Arithmetic instructions

L i l i t ti


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Immediate mode

ANL A, #dataORL A, #data

XRLA, #data

Direct modeANL A, Addr

ORL A, Addr

XRL A, Addr

ANL Addr, A

ORL Addr, A

XRL Addr, ARegister modeANL A, RnORL A, Rn

XRL A, Rn

RL A

RR ARLC A

RRC A

SWAP A

Indirect modeANL A, @Rn (n=0 or 1)

ORL A, @Rn

XRL A, @Rn

Logical instructions

P t l/B hi i t ti


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Conditional JumpCJNE A, #data, rel

CJNE Rn, #data, relCJNE @Ri, #data, rel

CJNE A, Addr, rel

JZ/JNZ reladdrJC/JNC reladdr

JB/JNB bitaddr, reladdr

DJNZ Rn, reladdr

DJNZ direct, reladdr

Unconditional JumpJMP @A+DPTR

SJMP reladdr

AJMP codeaddr

LJMP codeaddr

LCALL codeaddr

ACALL codeaddr

RET

RETI

Program control/Branching instructions


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8051

timer/counter

Tim s/C nt s P mmin


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The 8051 has 2 timers(Timer0 & Timer1),they can be used as

1. Timers to generate delays or.

2. Event counters to count events happening outside the microcontroller.Theseevents could represent the number of people passing through an entrance, orthe number of wheel rotations, or any other event that can be converted topulses.

Registers Used in Timer/Counter

1. TH0, TL0, TH1, TL1 (To hold the timer value)

2. TMOD (Timer mode register)3. TCON (Timer control register)

Both Timer 0 and Timer 1 are 16 bits wide,Since 8051 has an 8-bitarchitecture, each16-bits timer is accessed as two separate registers of lowbyte and high byte.These can be accessed like any other 8-bit registers.

MOV TL0,#26hMOV TH0,#50h

MOV TL1,#0ABh

MOV TH1,#0FFh

Timers/Counters Programming

Timers/Counters Pro rammin


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Timers/Counters Programming

Timer/Counter Block Diagram


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Once the timer is started it increments for every clock cycle until it reaches

FFFFh and for the next clock it rolls to 0, raising the timer overflow flag(TF0=1).

Timer/Counter Block Diagram


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Timer modes


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Timer modes

Mode1: 16-bit mode

Mode0: 13-bit mode

Mode2: 8-bit autoreload.

TCON Register


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TCON :Timer control register:

Upper nibble for timer/counter, lower nibble for interrupts.

TR(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. If we enable interrupt, TF=1 will trigger ISR.

TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0

Timer 1 Timer0 for Interrupt

(MSB) (LSB)

TCON Register

Steps for timer programming


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1.Configure the TMOD register indicating which timer (timer 0 or timer 1) is to be used

and which timer mode (0 or 1) is selected.

MOV TMOD,#01h TMOD=0x01

2. Load registers TL and TH with initial count value.

MOV TH0,#12 TH0=0x01

MOV TL0,#34 TL0=0x34

3. Start the timer.

SETB TR0 TR0=1

4. Keep monitoring the timer flag (TF) to see if it is raised, Get out of the loop when TF

becomes high.

here: JNB TF0,here while(!TF0); or while(TF0==0);

5. Stop the timer & clear the overflow flag for next operation

CLR TR0 TR0=0

CLR TF0 TF0=0

7. Go back to Step 2 to load TH and TL again.

Steps for timer programming

Timer delay calculation


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The timer works with a clock frequency of 1/12 of the XTAL frequency; therefore, we have

11.0592 MHz / 12 = 921.6 kHz as the timer frequency. As a result, each clock has a period

T = 1/921.6kHz = 1.085us. In other words, Timer increments for every1.085 us resulting in

delay = number of counts 1.085us.

STEPS:

Assume that XTAL = 11.0592 MHz .

And we know desired delay

how to find the values for the TH,TL ?

1. Divide the delay by 1.085 s and get n.2. Perform 65536 n3. Convert the result of Step 2 to hex (yyxx )4. Set TH = yy and TL = xx.

Timer delay calculation

Program to generate 500hz square wave on P2.0


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g m g q .

1ms

2ms

8051

P2.0

Assuming XTAL = 11.0592 MHz,

Solution:1. The period of the square wave1 / 500 = 2ms.2. The high or low portion of thesquare wave = 1 ms.3. 1ms / 1.085 s = 9214. 65536 921 = 64614 in decimal= FC66 in hex.5. TL1 = 0x66h and TH1 = 0xFCh.

Program to generate 500hz square wave on P2.0


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g g q

ORG 0000HMOV TMOD,#01H

Back: SETB P2.0LCALL delayCLR P2.0LCALL DelaySJMP Back

Delay: MOV TH0,#0FCh

MOV TL0.#66hSETB TR0

Here: JNB TF1, HereCLR TR0CLR TF0RET

END

#includeSbit sqr_wave=P2^0;

Void delay(){TH0=0xFC;TL0=0x66;TR0=1;

while(!TF0);TR0=0;TF0=0;

}

Void main(){TMOD=0x11;while(1)

{

sqr_wave=1;delay();

sqr_wave=0;delay();

}

}


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Serial

Communication



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Parallel Often 8 or more lines are used to

transfer the data in chunks of bytes.

Hence a lot of data is transmitted.

Used for short distance

communication.

Expensive

Ex: Computer to Printer

Serial

Here the data is transmitted bit by

bit on a single wire.

Used for long distance

communication. Cheaper compared to parallel.

Ex: Internet.

Computers transfer data in two methods:



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Serial CommunicationModes of communication

Simplex: Here the data is transmitted in only one

direction. Ex: PrinterHalf Duplex :Here the data is transmitted in both the

directions but not at the same time.

Ex: Walkie-Talkie

Full Duplex: Here the data is transmitted in both the

directions at the same time. Ex: mobile

Serial data communication uses two methods:

Synchronous: Here both transmitter and receiver are synchronized with respect to aclock. It is used to transmit a block of data.

Asynchronous : Here both transmitter and receiver generate their own clock(Baud-rate)

Universal Serial Protocols:

USRT: Universal Synchronous Receiver Transmitter.

UART: Universal Asynchronous Receiver Transmitter.



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Serial CommunicationBasics of serial communication: At the transmitting end, the byte of data

must be converted to serial bits usingparallel-in-serial-out shift register.

At the receiving end, there is aserial-in-parallel-out shift register

to receive the serial data

and pack them into byte.

When the distance is short, the digital signals can be transferred as it is on a

simple wire and requires no modulation. Ex: keyboard,mouse

If data is to be transferred on the telephone line, it must be converted

from 0s and 1s to audio tones, this conversion is performed by a device called amodem, Modulator/demodulator. Ex: internet

Shift Register Clock

Shift Register Clock

Parallel data in

serial data out

serial data in

Parallel data out



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Serial CommunicationPackaging (Framing):

Block-oriented data transfers use the synchronous method where as

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

The start bit is always one bit, but the stop bit can be one or two bits.

Start and Stop Bits:

The start bit is always a 0 (low) and the stop bit(s) is 1 (high)

RS232 St d d


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RS232 Standard Introduced in 1960 by Electronics

Industries Association (EIA).

Logic 1 is represented by -3 to -25 volt

Logic 0 is represented by 3 to 25 volt

To Connect TXD to RXD and RXD to

TXD from pc to 8051 we must use

max232 to convert signal from TTL levelto RS232 level

1 DCD

2 RD

3 TD

4 DTR

5 GND

6 DSR

7 RTS

8 CTS

9 RI



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Serial CommunicationBaud Rate and Bit Rate:

Baud Rate: It is defined as the number of signal changes per second. In

modems there are occasions where a single change of signal transfersseveral bits of data.

Bit Rate: It is defined as the number of bits transferred per second.

Both baud rate and bit rate are measured in bits per second(bps).

To allow the data transfer between two systems(8051 & PC) without anyerror, the baud rate of two systems should match.

Some of the standard baud rates supported by IBM PC:



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Serial CommunicationBaud Rate Generation:



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Serial CommunicationSBUF Register

SBUF is an 8-bit register used solely for serial communication.

For a byte of data to be transferred via theTxD line, it must be placed in the

SBUF register the moment a byte is written into SBUF, it is framed with the start

and stop bits and transferred serially via the TxD line.

SBUF holds the byte of data when it is received by 8051 RxD line.

When the bits are received serially via RxD, the 8051 deframes it by

eliminating the stop and start bits, making a byte out of the data received,

and then placing it in SBUF.

MOV SBUF,#A ;load SBUF=41H(65), ASCII of A

MOV SBUF,A ;copy accumulator into SBUF

MOV A,SBUF ;copy SBUF into accumulator

S i l t l (SCON) R i t


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Serial control (SCON) Register

SM2: used for multi processor communication.

REN: receive enable (by software enable/disable).

TB8 : transmit bit 8.RB8 : receive bit 8.

TI : transmit interrupt flag, set by HW once data is transmitted, and cleared by SW

RI : receive interrupt flag, set by HW after data is received ,and cleared by SW

SM0 RITIRB8TB8RENSM2SM1

7 6 5 4 3 2 1 0

SM0 SM1 MODE operation transmit rate0 0 0 shift register fixed (xtal/12)0 1 1 8-bit data 1 start variable (timer1)

and 1 stop bit.1 0 2 9 bit UART fixed (xtal/32 or xtal/64)1 1 3 9 bit UART variable (timer1)

SM0: mode specifier

SM1: mode specifier



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Steps to transfer character bytes serially:

1. Configure Timer1 in mode2(8-bit auto-reload) to generate the baud rate.

TMOD=0x20;

2. The TH1 is loaded with one of the values to set baud rate for serial data transfer.

TH1=0xFD; or TH1=-3; for 9600 baud rate.

3. Configure SCON register in mode1(8-bit data, 1-start and 1-stop bit).

SCON=0x50;

4. Start timer1 to generate the baud rate.

TR1=1;

5. Load the character byte to be transferred serially into SBUF register.SBUF=A; or SBUF=65 ;SBUF is loaded with the ascii value of A.

6. Wait till data is transmitted(ie Wait till TI becomes 1).

here: JNB TI, here or while(!TI) or while(TI==0);

7.Clear TI and go to step 5 to transfer the next byte.




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Program to transfer letter A serially at 9600 baud, continuously.MOV TMOD,#20H ; timer 1,mode 2(auto reload)

MOV TH1,# -3 ; 9600 baud rate

MOV SCON,#50H ; 8-bit, 1 stop, REN enabledSETB TR1 ; start timer1 to generate the baud rate

AGAIN: MOV SBUF,#A ; letter A to be transmitted

HERE: JNB TI,HERE ; wait till data is transmitted

CLR TI ; clear TI for next char

SJMP AGAIN ; keep sending A

Void main()

{

TMOD=0x20;

TH1=0xfd;

SCON=0x50;

TR1=1;

while(1)

{

SBUF=A;

while(TI==0);

TI=0;

}

}




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Steps to Receive and transfer character bytes serially:

1. Configure Timer1 in mode2(8-bit auto-reload) to generate the baud rate.

2. The TH1 is loaded with one of the values to set baud rate for serial data transfer.

3. Configure SCON register in mode1(8-bit data, 1-start and 1-stop bit).

4. Start timer1 to generate the baud rate.

5. Wait till data is received (ie Wait till RI becomes 1).

6. Clear RI and copy the received data from SBUF into accumlator.

7. Load the received data into SBUF register for transmission.

8. Wait till data is transmitted(ie Wait till TI becomes 1).

9.Clear TI and go to step 5 to continue the process.


Ser a ommun cat on


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Program to receive and transfer characters serially at 9600 baud, continuously.MOV TMOD,#20H ; timer 1,mode 2(auto reload)

MOV TH1,# -3 ; 9600 baud rate

MOV SCON,#50H ; 8-bit, 1 stop, REN enabled

SETB TR1 ; start timer1 to generate the baud rate

HERE: JNB RI,HERE; wait till data is receivedCLR RI ; clear RI to receive next char

MOV A, SBUF; copy the received char into accumlator.

AGAIN: MOV SBUF, A ; transmit the received char.

WAIT : JNB TI,WAIT ; wait till data is transmitted.

CLR TI ; clear TI for next char

SJMP HERE; continue the process

Void main()

{ char ch;

TMOD=0X20;

TH1=0XFD;

SCON=0X50;

TR1=1;

while(1)

{while(RI==0);

RI=0;

ch=SBUF;

SBUF=ch;

while(TI==0);

TI=0;

}

}

Ser a ommun cat on


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Interrupts Programming



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n rrup r gr mm ng An in terruptis an external or internal event that interrupts the

microcontroller to inform it that a device needs its service. The program

which is associated with the interrupt is called the in terrupt service rout in e

(ISR) orin terrupt handler.

Interrupts vs. Polling

A single microcontroller can serve several devices. There are two ways to do that:

Polling:

The microcontroller continuously monitors the status of the device to checkwhether it needs service and provides the service if required.

After that it moves on to monitor the next device until every one is serviced.

The polling method is not efficient, since it wastes much of the controllers time

by polling devices that do not need service.

Interrupts:

Here the device itself informs (interrupts) the controller whenever it needs the

service.

Each device can get the attention of the controller based on the priority. Where as

Polling uses Round-Robin fashion hence it is not possible to assign the priority.



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p g mm gClassification of interrupts: Interrupts can be classified as

1: Maskable and Non-Maskable interrupts

Maskable interrupts : The service can be delayed or rejected by the controller just bydisabling the interrupts.

Non-Maskable interrupts : The service cannot be rejected but it may be delayed

depending on the priority of the other interrupts.

2: Vectored and non-vectored interrupts. Vectored interrupts : The address of the interrupt service routine is hardwired or fixed.

Non- Vectored interrupts : Here the device has to provide the address of the service

routine.

For every interrupt, there must be an interrupt service routine (ISR),or interrupt handler.

When an interrupt is invoked, the microcontroller runs the interrupt service

routine.

For every interrupt, there is a fixed location in memory that holds the address

of its ISR. The group of memory locations set aside to hold the addresses of ISRs is

called interrupt vector table.


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Steps in executing an interrupt

Upon activation of an interrupt, the microcontroller goes

through the following steps It finishes the instruction it is executing and saves the address of the

next instruction (PC) on the stack

It also saves the current status of all the interrupts internally (i.e: not onthe stack)

It jumps to a fixed location in memory, called the interrupt vector table,

that holds the address of the ISR. The microcontroller gets the address of the ISR from the interrupt

vector table and jumps to it and starts to execute the interrupt servicesubroutine until it reaches the last instruction of the subroutine which isRETI (return from interrupt)

Upon executing the RETI instruction, the microcontroller returns to theplace where it was interrupted. First, it gets the program counter (PC)address from the stack by popping the top two bytes of the stack intothe PC and then it starts to execute from that address



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p g gSix interrupts are allocated as follows: Reset : power-on- reset.

Two interrupts are set aside for the timers one for timer 0 and one for timer 1.

Two interrupts are set aside for hardware external interrupts. P3.2 and P3.3 are

for the external hardware interrupts INT0 (or EX1), and INT1 (or EX2).

Serial communication has a single interrupt that belongs to both receive and

transfer.

Interrupt Vectors:Each interrupt has a specific place in code memory where program execution

(interrupt service routine) begins.



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p g g

Upon reset, all interrupts are disabled (masked), meaning that none will be

responded to by the microcontroller if they are activated. The interrupts must be

enabled by software in order for the microcontroller to respond to them. There is aregister called IE (interrupt enable) that is responsible for enabling (unmasking)

Interrupt Enable (IE) register



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p g gBy bit operation

SETB EA EA=1 ;Enable AllSETB ET0 ET0=1 ;Enable Timer0 ovrf

SETB ET1 ET1=1 ;Enable Timer1 ovrfSETB EX0 EX0=1 ;Enable INT0SETB EX1 EX1=1 ;Enable INT1SETB ES ES=1 ;Enable Serial port

By mov instructionMOV IE, #10010110B;

SETB IE.7

SETB IE.1

SETB IE.3

SETB IE.0

SETB IE.2

SETB IE.4

Asm program to generate 500hz and 2khz square waveson P1 0 & P1 1


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on P1.0 & P1.1ORG 0000H

LJMP MAINORG 000BH

LJMP T0ISR

ORG 001BHLJMP T1ISR

ORG 0030HMAIN: MOV TMOD,#11H

MOV TH0,#0FChMOV TL0,#066h

MOV TH1,#0FFhMOV TL1,#019hSETB TR0SETB TF1MOV IE,#8AHSJMP $

T0ISR: MOV TH0,#0FChMOV TL0,#066hCPL P1.0RETI

T1ISR: MOV TH1,#0FFhMOV TL1,#19hCPL P1.1

RETIEND

0.25ms

0.5ms

1ms

2ms

P1.1

8051

P1.0

Notice that

There is no need for a CLR TFxinstruction in timer ISR ,8051

automatically clears the TF internally

upon jumping to ISR.

C program to generate 500hz and 2khz square waves onP1 0 & P1 1 simultanously


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P1.0 & P1.1 simultanously

#includeSbit Sqr1=P1^0;Sbit sqr2=P1^1;

Void timer0_isr() interrupt 1{sqr1=!sqr1;TH0=0xFC;TL0=0x66;

}Void timer1_isr() interrupt 3{sqr2=!sqr2;TH1=0xFF;TL1=0x19;

}

Void main(){TMOD=0x11;TH0=0xFC; TL0=0x66;TH1=0xFF; TL1=0x19;IE=0x8A;while(1);}

Timer calculation for 500hz:

1. T = 1 / 500 = 2 ms, period of square wave.

2. 1 / 2 of it for the high and low portion of the

pulse is 1 ms.

3. 1ms / 1.085 us = 9216 and 65536 9216 =

56320 in decimal, and in hex it is DC00H.

4. TL = 00 and TH = DC (hex).

Timer calculation for 2khz:

1. T = 1 / 2000 = .5 ms, period of square wave.

2. 1 / 2 of it for the high and low portion.

ie pulse width=0.25 ms.

1. 0.25ms / 1.085 us = 9216 and 65536 9216 =

56320 in decimal, and in hex it is DC00H.

2. TL = 00 and TH = DC (hex).


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Led Interfacing


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g

Common anode: Here all the anode terminals of leds are shorted(made common)

and connected to VCC, so to turn on a particular led a logic 0(0V) has to be

applied.

LED (Light emitting diode): It is a type of diode which emits

the light whenever it is connected in forward bias.Led can be

Connected in two fashions ie.common anode & commoncathode.

Common cathode: Here all the cathode terminals of leds

areshorted(made common) and connected to GND, so to

turn on a particular led a logic 1(5V) has to be applied.

GND(0v)

Common cathode Common anode.

VCC(5v)

Program to blink the Led continuously


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g y#include

#define LED P2

void delay(unsigned int n){

while(n--);

}

void main()

{while(1)

{

LED=0xff ; //turn on the leds

delay(50000);

LED=0x00 ; //turn off the ledsdelay(50000);

}

}

Seven Segment Display


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g p y1. It is composed of 8 LEDs arranged as a

rectangle.

2. Segments are marked with the lettersfrom a to g, plus dp, as shown in figure.

3. Here the chars are displayed just by

turning on/off the respective leds. To

display a particular digit a seven segmentcode has to be generated and sent to the

port as shown in the figure.To display 5

we have to turn ON a,c,d,f,g and OFF

b,e,dp(Assuming the segment to be of

common cathode).

4. Useful for displaying the digits 0 through

9, and some characters.

Seven Segment Display Code for common cathode


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a

b

c

f

ed

f

e

a

b

e

g

d

a

b

c

g

d

b

c

fg

a

c

fg

d

a

c

f

e

g

d

a

b

c

a

b

c

f

e

g

d

a

b

c

fg

d

BCD p g f e d c b a

7_seg

hex

0000 0 0 1 1 1 1 1 1 3f

0001 0 0 1 1 0 0 0 0 30

0010 0 1 0 1 1 0 1 1 5b

0011 0 1 0 0 1 1 1 1 4f

0100 0 1 1 0 0 1 1 0 660101 0 1 1 0 1 1 0 1 6d

0110 0 1 1 1 1 1 0 1 7d

0111 0 0 0 0 0 1 1 1 07

1000 0 1 1 1 1 1 1 1 7f

1001 0 1 1 0 1 1 1 1 6f

7-segment displays come in 2 configurations:

Common cathode: Logic 1 (5v) should

be provided to turn on a particularsegment.

Common Anode Common Cathode.

Common anode: Logic 0 (0v) should be

provided to turn on a particular segment.

Program to display decimal upcounter(0-9)


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#include

#define seven_segment P2

void main(){

char a[]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,

0x7d,0x07,0x7f,0x6f};

unsigned int i,j;

while(1){

for(i=0;i


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g g p y

LCD Interfacing


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1. Liquid Crystal Displays (LCDs)

2. cheap and easy way to display all letters of

alphabet, greek letters, punctuation marks,

mathematical symbols etc.3. Available in Various configurations (1 line by

20 char upto 8 lines X 80 chars ).

g

E

R/W

RS

DB7DB0

LCD

controller

communications

bus

Microcontroller

8

LCD Module

Pinout8 data pins D7:D0RS: Data or Command Register Select

R/W: Read or WriteE: Enable (Latch data)

RS Register SelectRS = 0 Command RegisterRS = 1 Data Register

R/WRead/WriteR/W = 0 writeR/W= 1 Read

E EnableUsed to latch the data present on the datapins.

D0 D7Bi-directional data/command pins.

Alphanumeric characters are sent in ASCIIformat.

LCD Interfacing


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g

LCD Commands


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Program to display hello, world on lcd


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Steps to send command to lcd:1. Send the command to lcd databus.

databus=cmd;

2. Select the command Register.RS=0;

3. Write operation.

RW=0;

4. High-to-Low pulse at the enable pin.

EN=1

delay();

EN=0;

Steps to send Data to lcd:1. Send the ASCII value of data to lcd databus.

databus=dat;

2. Select the Data Register.

RS=1;

3. Write operation.RW=0;

4. High-to-Low pulse at the enable pin.

EN=1

delay();

EN 0

#include

#define databus P2

sbit rs= P0^0;

sbit rw= P0^1;

sbit en= P0^2;

void lcd_cmd( char cmd)

{

unsigned int i;

databus=cmd;

rs=0;

rw=0;en=1;

for(i=0;i

final 8051 printout

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