Project report

On

Digital clock using LCD display

ACKNOWLEDGEMENT

Apart from the efforts of me, the success of this project depends largely on

the encouragement and guidance of many others. I take this opportunity to

express my gratitude to the people who have been instrumental in the

successful completion of this project.

I would like to show my greatest appreciation to Er.Vishu Grover from

Innovation Research and Development. I can’t say thank you enough for

their tremendous support and help. I feel motivated and encouraged every

time. Without their Encouragement and Guidance this project would not

have materialized.

The guidance and support received from my friend (name) who contributed

and are contributing to this project, was vital for the success of the project. I

am grateful for their constant support and help.

DECLARATION

We hereby declare that the project work entitled (“Digital Clock”) is an

authentic records of my own work carried out at innovation research and

Development. Internship Project for the award of Degree of B.TECH-ECE,

(college name) under the guidance of VISHU GROVER, during July to

December 2010

Name of Student:

Registration Number

ABSTRACT:This project incorporates the functionality of a digital clock and a digital thermometer. The digital clock works in 12 hour mode and is configured by programming the 8051 microcontroller (AT89C51). The program uses a delay function for producing a delay of 1 second. The clock and alarm times can be set through a set of external tactile switches.The digital thermometer employs a temperature sensor LM35. The sensor responds to the temperature change by giving varying output. These analog signals of LM35 are converted to digital equivalent by ADC0804. The reference voltage (Vref) should be set properly corresponding to the desired temperature range. The data bits are taken as input by the microcontroller at port P0. The microcontroller AT89C51 also gives control signals to ADC0804.

This project is a clock that displays the time and date on seven segment led displays. Two buttons are used to set the time and date. The program takes care of changing the date and keeping track of leap years. In this project, we have built a digital clock with 12 hour count time. The clock runs from 00:00 to 11:59 and then back to 00:00. Our display has four digits, two digits for minutes and two for hour. The specialty of this clock is that it has very low power consumption and condensed layout.

SUMMARY:

This project works as a digital clock wherein a user can also set alarm. Additionally, it also works as a digital thermometer to specify the ambient temperature. Both, the clock and temperature are displayed on a 16x2 LCD screen using the 8051 microcontroller (AT89C51). AT89C51 is an eight bit controller which belongs to the 8051 family of microcontrolers.

This clock works in 12 hour mode and is configured by programming the microcontroller AT89C51. The program uses a delay function for producing a delay of 1 second.The connections in the circuit are as following: port P2 of microcontroller is used as data input port which is connected to data pins (7-14) of LCD. P3^0, P3^1 and P3^6 pins of microcontroller are connected to control pins RS, RW and EN of LCD. P1^0, P1^1, P1^2 and P1^3 pins of microcontroller are connected to tactile switches to take manual inputs. On reset, the LCD prompts the user to set time. Only the hour and minute components can be set by pressing the corresponding switches, repeatedly. These switches are made active low and so they provide ground to the corresponding input pins of the controller. The AM/PM mode is set by toggling the switch between ground and Vcc. Ground would set the clock in AM mode while Vcc would set it in PM mode. The clock starts when start pin is connected to Vcc by pressing

the switch. The set time is displayed on LCD screen and changes as the time passes on. Seconds are increased after every one second by making use of delay function. As second reaches 59, minute is incremented by one and second is reset to 0. Similarly, as minute reaches 59, hour is increased by one and minute is set to 0. After hour reaches 11, minute reaches 59 and second reaches 59, all of them are set to 0 and the AM/PM mode is changed accordingly.  

Circuit description    

Components used

Preset A preset is a three legged electronic component which can be made to offer varying resistance in a circuit. The resistance is varied by adjusting the rotary control over it. The adjustment can be done by using a small screw driver or a similar tool. The resistance does not vary linearly but rather varies in exponential or logarithm...

AT89C51 or 89C51 microcontroller AT89C51 is an 8-bit microcontroller and belongs to Atmel's 8051 family. AT89C51 has 4KB of Flash programmable and erasable read only memory (PEROM) ...

LCD LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment...

Interfacing switch with 8051

Lcd interfacing with microcontroller

Introduction

The most commonly used Character based LCDs are based on Hitachi's HD44780 controller or other which are compatible with HD44580. In this tutorial, we will discuss about character based LCDs, their interfacing with various microcontrollers, various interfaces (8-bit/4-

bit), programming, special stuff and tricks you can do with these simple looking LCDs which can give a new look to your application.

For Specs and technical information HD44780 controller Click Here

Pin Description

The most commonly used LCDs found in the market today are 1 Line, 2 Line or 4 Line LCDs which have only 1 controller and support at most of 80 charachers, whereas LCDs supporting more than 80 characters make use of 2 HD44780 controllers.

Most LCDs with 1 controller has 14 Pins and LCDs with 2 controller has 16 Pins (two pins are extra in both for back-light LED connections). Pin description is shown in the table below.

Figure 1: Character LCD type HD44780 Pin diagram

Pin No. Name DescriptionPin no. 1 VSS Power supply (GND)Pin no. 2 VCC Power supply (+5V)Pin no. 3 VEE Contrast adjustPin no. 4 RS 0 = Instruction input

1 = Data inputPin no. 5 R/W 0 = Write to LCD module

1 = Read from LCD modulePin no. 6 EN Enable signalPin no. 7 D0 Data bus line 0 (LSB)Pin no. 8 D1 Data bus line 1Pin no. 9 D2 Data bus line 2Pin no. 10 D3 Data bus line 3Pin no. 11 D4 Data bus line 4Pin no. 12 D5 Data bus line 5Pin no. 13 D6 Data bus line 6Pin no. 14 D7 Data bus line 7 (MSB)

Table 1: Character LCD pins with 1 Controller

Pin No. Name DescriptionPin no. 1 D7 Data bus line 7 (MSB)Pin no. 2 D6 Data bus line 6

Pin no. 3 D5 Data bus line 5Pin no. 4 D4 Data bus line 4Pin no. 5 D3 Data bus line 3Pin no. 6 D2 Data bus line 2Pin no. 7 D1 Data bus line 1Pin no. 8 D0 Data bus line 0 (LSB)Pin no. 9 EN1 Enable signal for row 0 and 1 (1stcontroller)Pin no. 10 R/W 0 = Write to LCD module

1 = Read from LCD modulePin no. 11 RS 0 = Instruction input

1 = Data inputPin no. 12 VEE Contrast adjustPin no. 13 VSS Power supply (GND)Pin no. 14 VCC Power supply (+5V)Pin no. 15 EN2 Enable signal for row 2 and 3 (2ndcontroller)Pin no. 16 NC Not Connected

Table 2: Character LCD pins with 2 Controller

Usually these days you will find single controller LCD modules are used more in the market. So in the tutorial we will discuss more about the single controller LCD, the operation and everything else is same for the double controller too. Lets take a look at the basic information which is there in every LCD.

►DDRAM - Display Data RAM

Display data RAM (DDRAM) stores display data represented in 8-bit character codes. Its extended capacity is 80 X 8 bits, or 80 characters. The area in display data RAM (DDRAM) that is not used for display can be used as general data RAM. So whatever you send on the DDRAM is actually displayed on the LCD. For LCDs like 1x16, only 16 characters are visible, so whatever you write after 16 chars is written in DDRAM but is not visible to the user.

Figures below will show you the DDRAM addresses of 1 Line, 2 Line and 4 Line LCDs.

Figure 2: DDRAM Address for 1 Line LCD

Figure 3: DDRAM Address for 2 Line LCD

Figure 4: DDRAM Address for 4 Line LCD

►CGROM - Character Generator ROM

Now you might be thinking that when you send an ascii value to DDRAM, how the character is displayed on LCD? so the answer is CGROM. The character generator ROM generates 5 x 8 dot or 5 x 10 dot character patterns from 8-bit character codes (see Figure 5 and Figure 6 for more details). It can generate 208 5 x 8 dot character patterns and 32 5 x 10 dot character patterns. Userdefined character patterns are also available by mask-programmed ROM.

Figure 5: LCD characters code map for 5x8 dots

Figure 6: LCD characters code map for 5x10 dots

As you can see in both the code maps, the character code from 0x00 to 0x07 is occupied by the CGRAM characters or the user defined characters. If user want to display the fourth custom character then the code to display it is 0x03 i.e. when user send 0x03 code to the LCD DDRAM then the fourth user created charater or patteren will be displayed on the LCD.

►CGRAM - Character Generator RAM

As clear from the name, CGRAM area is used to create custom characters in LCD. In the character generator RAM, the user can rewrite character patterns by program. For 5 x 8 dots, eight character patterns can be written, and for 5 x 10 dots, four character patterns can be written. Later in this tutorial i will explain how to use CGRAM area to make custom character and also making animations to give nice effects to your application.

►BF - Busy Flag

Busy Flag is an status indicator flag for LCD. When we send a command or data to the LCD for processing, this flag is set (i.e BF =1) and as soon as the instruction is executed successfully this flag is cleared (BF = 0). This is helpful in producing and exact ammount of delay. for the LCD processing.

To read Busy Flag, the condition RS = 0 and R/W = 1 must be met and The MSB of the LCD data bus (D7) act as busy flag. When BF = 1 means LCD is busy and will not accept next command or data and BF = 0 means LCD is ready for the next command or data to process.

►Instruction Register (IR) and Data Register (DR)

There are two 8-bit registers in HD44780 controller Instruction and Data register. Instruction register corresponds to the register where you send commands to LCD e.g LCD shift command, LCD clear, LCD address etc. and Data register is used for storing data which is to be displayed on LCD. when send the enable signal of the LCD is asserted, the data on the pins is latched in to the data register and data is then moved automatically to the DDRAM and hence is displayed on the LCD.Data Register is not only used for sending data to DDRAM but also for CGRAM, the address where you want to send the data, is decided by the instruction you send to LCD. We will discuss more on LCD instuction set further in this tutorial.

►Commands and Instruction set

Only the instruction register (IR) and the data register (DR) of the LCD can be controlled by the MCU. Before starting the internal operation of the LCD, control information is temporarily stored into these registers to allow interfacing with various MCUs, which operate at different speeds, or various peripheral control devices. The internal operation of the LCD is determined by signals sent from the MCU. These signals, which include register selection signal (RS), read/write signal (R/W), and the data bus (DB0 to DB7), make up the LCD instructions (Table 3). There are four categories of instructions that:

Designate LCD functions, such as display format, data length, etc.

Set internal RAM addresses Perform data transfer with internal RAM Perform miscellaneous functions

Table 3: Command and Instruction set for LCD type HD44780

Although looking at the table you can make your own commands and test them. Below is a breif list of useful commands which are used frequently while working on the LCD.

No. Instruction Hex Decimal1 Function Set: 8-bit, 1 Line, 5x7 Dots 0x30 482 Function Set: 8-bit, 2 Line, 5x7 Dots 0x38 563 Function Set: 4-bit, 1 Line, 5x7 Dots 0x20 324 Function Set: 4-bit, 2 Line, 5x7 Dots 0x28 405 Entry Mode 0x06 66 Display off Cursor off

(clearing display without clearing DDRAM content) 0x08 8 7 Display on Cursor on 0x0E 148 Display on Cursor off 0x0C 129 Display on Cursor blinking 0x0F 1510 Shift entire display left 0x18 24

12 Shift entire display right 0x1C 3013 Move cursor left by one character 0x10 16 14 Move cursor right by one character 0x14 20 15 Clear Display (also clear DDRAM content) 0x01 116 Set DDRAM address or coursor position on display 0x80+add* 128+add*17 Set CGRAM address or set pointer to CGRAM location 0x40+add** 64+add**

Table 4: Frequently used commands and instructions for LCD

* DDRAM address given in LCD basics section see Figure 2,3,4** CGRAM address from 0x00 to 0x3F, 0x00 to 0x07 for char1 and so on..

The table above will help you while writing programs for LCD. But after you are done testing with the table 4, i recommend you to use table 3 to get more grip on working with LCD and trying your own commands. In the next section of the tutorial we will see the initialization with some of the coding examples in C as well as assembly.

Sending Commands to LCD

To send commands we simply need to select the command register. Everything is same as we have done in the initialization routine. But we will summarize the common steps and put them in a single subroutine. Following are the steps:

Move data to LCD port select command register select write operation send enable signal wait for LCD to process the command

Keeping these steps in mind we can write LCD command routine as.

CODE:;Ports used are same as the previous example;Routine to send command to LCD

LCD_command:         mov   LCD_data,A     ;Move the command to LCD port         clr   LCD_rs         ;Selected command register         clr   LCD_rw         ;We are writing in instruction register         setb  LCD_en         ;Enable H->L         clr   LCD_en         acall LCD_busy       ;Wait for LCD to process the command         ret                  ;Return from busy routine

; Usage of the above routine; A will carry the command for LCD; e.g. we want to send clear LCD command;; mov   a,#01H         ;01H is command for clearing LCD; acall LCD_command    ;Send the command

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:void LCD_command(unsigned char var){     LCD_data = var;      //Function set: 2 Line, 8-bit, 5x7 dots     LCD_rs   = 0;        //Selected command register     LCD_rw   = 0;        //We are writing in instruction register     LCD_en   = 1;        //Enable H->L     LCD_en   = 0;     LCD_busy();          //Wait for LCD to process the command}// Using the above function is really simple// var will carry the command for LCD// e.g.//// LCD_command(0x01);

Setting cursor position on LCDTo set the cursor position on LCD, we need to send the DDRAM address...

CODE:Bit7  6   5   4   3   2   1   0 1   AD6 AD5 AD4 AD3 AD2 AD1 AD0

The seventh bit is always 1, and bit 0 to 7 are DDRAM address (See the introduction section of LCD). so if you want to put the cursor on first position the address will be '0000000B' in binary and 7th bit is 1. so address will be 0x80, so for DDRAM all address starts from 0x80.

For 2 line and 16 character LCD. The adress from 0x80 to 0x8F are visible on first line and 0xC0 to 0xCF is visible on second line, rest of the DDRAM area is still available but is not visible on the LCD, if you want to check this thing, then simply put a long sting greater than 16 character and shift the entire display, you will see all the missing character coming from the back.. this way you can make scrolling line on LCD (see more on shifting display in commands section).

Below is an example for setting cursor position on LCD.

CODE:;We are placing the cursor on the 4th position;so the DDRAM address will be 0x03;and the command will be 0x80+0x03 = 0x83mov a,#83H           ;load the commandacall LCD_command    ;send command to LCD

CODE:// to do the same thing is C// as we done beforeLCD_command(0x83);

►Sending Data to LCD

To send data we simply need to select the data register. Everything is same as the command routine. Following are the steps:

Move data to LCD port select data register select write operation send enable signal wait for LCD to process the data

Keeping these steps in mind we can write LCD command routine as.

CODE:;Ports used are same as the previous example;Routine to send data (single character) to LCD

LCD_senddata:         mov   LCD_data,A     ;Move the command to LCD port         setb  LCD_rs         ;Selected data register         clr   LCD_rw         ;We are writing         setb  LCD_en         ;Enable H->L         clr   LCD_en         acall LCD_busy       ;Wait for LCD to process the data         ret                  ;Return from busy routine

; Usage of the above routine; A will carry the character to display on LCD; e.g. we want to print A on LCD;; mov   a,#'A'         ;Ascii value of 'A' will be loaded in accumulator; acall LCD_senddata   ;Send data

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:void LCD_senddata(unsigned char var){     LCD_data = var;      //Function set: 2 Line, 8-bit, 5x7 dots     LCD_rs   = 1;        //Selected data register     LCD_rw   = 0;        //We are writing     LCD_en   = 1;        //Enable H->L     LCD_en   = 0;     LCD_busy();          //Wait for LCD to process the command}// Using the above function is really simple// we will pass the character to display as argument to function// e.g.//// LCD_senddata('A');

Now you have seen that its really easy to send command and data to LCD. Now what if we have a string to send to LCD? how we are going to do that?

Is simple, we will store the LCD string in the ROM of controller and call the string character by character. A simple exmple is shown below.

CODE:;Sending string to LCD Example

LCD_sendstring:         clr   a                 ;clear Accumulator for any previous data         movc  a,@a+dptr         ;load the first character in accumulator         jz    exit              ;go to exit if zero         acall lcd_senddata      ;send first char         inc   dptr              ;increment data pointer         sjmp  LCD_sendstring    ;jump back to send the next characterexit:         ret                     ;End of routine

; Usage of the above routine; DPTR(data pointer) will carry the address; of string to send to LCD.; e.g. we want to print "LCD Tutorial" on LCD then;; mov   dptr,#my_string   ;my_string is the label where the string is stored; acall LCD_sendstring    ;Send string;; To store a string..; my_string:; DB   "LCD Tutorial", 00H; 00H indicate that string is finished.

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:void LCD_sendstring(unsigned char *var){     while(*var)              //till string ends       LCD_senddata(*var++);  //send characters one by one}// Using the above function is really simple// we will pass the string directly to the function// e.g.//// LCD_sendstring("LCD Tutorial"); 

Now we are ready with sending data and sending command to LCD. Now the last and final section which is creating custom characters or patterns to display on LCD. Please proceed to the next section to read more.

4-bit Initialization

Initialization of LCD is completed only after the reset sequence and basic initialization commands. We have already discussed about the reset sequence of the lcd in the previous section. So lets look at the programming now...

►Assembly Program

CODE:;In this whole 4-bit tutorial LCD is connected to;my controller in following way...;D4 - P3.0;D5 - P3.1;D6 - P3.2;D7 - P3.3;EN - P3.7;RS - P3.5

        lcd_port equ P3         ;LCD connected to Port3        en equ P3.7             ;Enable connected to P3.7        rs equ P3.5             ;Register select to P3.5       lcd_reset:                  ;LCD reset sequence        mov lcd_port, #0FFH        mov delay,#20           ;20mS delay        acall delayms        mov lcd_port, #83H      ;Data = 30H, EN = 1, First Init        mov lcd_port, #03H      ;Data = 30H, EN = 0        mov delay,#15           ;Delay 15mS        acall delayms        mov lcd_port, #83H      ;Second Init, Data = 30H, EN = 1

        mov lcd_port, #03H      ;Data = 30H, EN = 0        mov delay,#5            ;Delay 5mS        acall delayms        mov lcd_port, #83H      ;Third Init        mov lcd_port, #03H        mov delay,#5            ;Delay 5mS        acall delayms        mov lcd_port, #82H      ;Select Data width (20H for 4bit)        mov lcd_port, #02H      ;Data = 20H, EN = 0        mov delay,#5            ;Delay 5mS        acall delayms        ret

lcd_init:        acall lcd_reset         ;Call LCD Reset sequence        mov a,#28H              ;4-bit, 2 line, 5x7 dots        acall lcd_cmd           ;Call LCD command        mov a,#0CH              ;Display ON cursor OFF        acall lcd_cmd           ;Call LCD command        mov a,#06H              ;Set entry mode (Auto increment)        acall lcd_cmd           ;Call LCD command        mov a,#80H              ;Bring cursor to line 1        acall lcd_cmd           ;Call LCD command        ret 

►C Program

CODE://The pins used are same as explained earlier#define lcd_port    P3

//LCD Registers addresses#define LCD_EN      0x80#define LCD_RS      0x20

void lcd_reset(){        lcd_port = 0xFF;        delayms(20);        lcd_port = 0x03+LCD_EN;        lcd_port = 0x03;        delayms(10);        lcd_port = 0x03+LCD_EN;        lcd_port = 0x03;        delayms(1);        lcd_port = 0x03+LCD_EN;        lcd_port = 0x03;        delayms(1);        lcd_port = 0x02+LCD_EN;        lcd_port = 0x02;        delayms(1);}

void lcd_init (){        lcd_reset();         // Call LCD reset        lcd_cmd(0x28);       // 4-bit mode - 2 line - 5x7 font.         lcd_cmd(0x0C);       // Display no cursor - no blink.

        lcd_cmd(0x06);       // Automatic Increment - No Display shift.        lcd_cmd(0x80);       // Address DDRAM with 0 offset 80h. } 

►Sending Dommand/Data to LCD in 4-bit mode►Assembly Program

CODE:lcd_cmd:                  ;LCD command Routine        mov temp,a            ;Save a copy of command to temp        swap a                ;Swap to use higher nibble        anl a,#0FH            ;Mask the first four bits        add a,#80H            ;Enable = 1, RS = 0        mov lcd_port,a        ;Move it to lcd port        anl a,#0FH            ;Enable = 0, RS = 0        mov lcd_port,a        ;Move to lcd port

        mov a,temp            ;Reload the command from temp        anl a,#0FH            ;Mask first four bits        add a,#80H            ;Enable = 1        mov lcd_port,a        ;Move to port        anl a,#0FH            ;Enable = 0        mov lcd_port,a        ;Move to lcd port

        mov delay,#1          ;delay 1 ms        acall delayms        ret

lcd_dat:                  ;LCD data Routine        mov temp,a            ;Keep copy of data in temp        swap a                ;We need higher nibble        anl a,#0FH            ;Mask first four bits        add a,#0A0H           ;Enable = 1, RS = 1        mov lcd_port,a        ;Move to lcd port        nop        clr en                ;Enable = 0

        mov a,temp            ;Reload the data from temp        anl a,#0FH            ;we need lower nibble now        add a,#0A0H           ;Enable = 1, RS = 1        mov lcd_port,a        ;Move to lcd port        nop        clr en                ;Enable = 0

        mov delay,#1          ;Delay 1mS        acall delayms        ret 

►C Program

CODE:void lcd_cmd (char cmd){        lcd_port = ((cmd >> 4) & 0x0F)|LCD_EN;

        lcd_port = ((cmd >> 4) & 0x0F);

        lcd_port = (cmd & 0x0F)|LCD_EN;        lcd_port = (cmd & 0x0F);

        delayus(200);        delayus(200);}

void lcd_data (unsigned char dat){        lcd_port = (((dat >> 4) & 0x0F)|LCD_EN|LCD_RS);        lcd_port = (((dat >> 4) & 0x0F)|LCD_RS);               lcd_port = ((dat & 0x0F)|LCD_EN|LCD_RS);        lcd_port = ((dat & 0x0F)|LCD_RS);

        delayus(200);        delayus(200);

 Basic Circuit for 8051 

                                                                                                   

           

8051 PIN OUT 

  Power - Vcc, Vss Reset - RST Crystal - XTAL[1,2] External device interfacing      – EA, ALE, PSEN, WR, RD  I/O Port      – P0[7;0], P1[7:0], P2[7:0], P3    P3 is shared with control lines        – Serial I/O RxD, TxD,         – external interrupts INT0,  INT1         – Counter control T0, T1    P0 and P2 are multiplexed with Address and Data bus  

 

BASIC CIRCUIT -THAT MAKES 8051 WORKS.

 

                                                     

EA/VP PinThe EA on pin 31 is tied high to make the 8051 executes program from Internal ROM

 

Reset CircuitRESET is an active High input  When RESET is set to High, 8051 goes back to the power on state.The 8051 is reset by holding the RST high for at least two machine cycles and then returning it low.

  Power-On Reset

    - Initially charging of capacitor makes RST High    - When capacitor charges fully it blocks DC.

  Manual reset

     -closing the switch momentarily will make RST High.

 After a reset, the

program counter is loaded with 0000H but the content of on-chip RAM is not affected. 

 

 

 

 

 

 

Note: content of on-chip RAM is not affected by Reset.

 

Oscillator Circuit

The 8051 uses the crystal for precisely that: to synchronize it’s operation. Effectively, the 8051 operates using what are called "machine cycles." A single machine cycle is the minimum amount of time in which a single 8051 instruction can be executed. although many instructions take multiple cycles. 

8051 has an on-chip oscillator. It needs an external crystal thats decides the operating frequency of the 8051.

 This can be achieved in two ways,,

The crystal is connected to pins 18 and 19 with stabilizing capacitors. 12 MHz (11.059MHz) crystal is often used and the capacitance ranges from 20pF to 40pF.

The oscillator can also be a TTL clock source connected with a NOT gate as shown

Register Content

Register Content

Program counter 0000h IP XXX00000b

Accumulator 00h IEv 0XX00000b

B register 00h All timer registers 00h

PSW 00h SCON 00hSP 07h SBUF 00h

DPTR 0000h PCON (HMOS)

0XXXXXXXbv

All ports FFh PCON (CMOS)v 0XXX0000b

 

How fast 8051 works ?

A cycle is, in reality, 12 pulses of the crystal. That is to say, if an instruction takes one machine cycle to execute, it will take 12 pulses of the crystal to execute. Since we know the crystal is pulsing 11,059,000 times per second and that one machine cycle is 12 pulses, we can calculate how many instruction cycles the 8051 can execute per second:

11,059,000 / 12 = 921,583

Why is such an oddball crystal frequency?

11.0592 MHz crystals are often used because it can be divided to give you exact clock rates for most of the common baud rates for the UART, especially for the higher speeds (9600, 19200). Despite the "oddball" value, these crystals are readily available and commonly used.

 

Power Supply

 

C1-1000 mf ,C2-100 mf

The 78L05 is a 5V regulator. The input voltage ranges

from 7V to 35V and the output voltage is about 5V.

 

 

Using Ports for I/O Operation

8051 is TTL logic device. TTL logic has two levels: Logic "High" (1) and logic "Low" (0). The voltage and current involved for the two levels are as follows:

 

Level 

 Voltage Current

High Above 2.4V

Virtually no current flow

Low Below 0.9V

1.6mA Sinking current from TTL input to ground(Depends on logic family)

 

 Port functions

Ports   Function

Port 0(Pin 32-39)

Dual-purpose port- 1. general purpose I/O Port.                                 2. multiplexed address & data bus                                                           Open drain outputs

Port 1(Pin 1-8) 

 Dedicated I/O port – Used solely  for interfacing to external devices                                               Internal pull-ups

Port 2(Pin 21-28) 

Dual-purpose port-  1. general purpose I/O port.                                   2. a multiplexed address & data bus.                                  Internal pull-ups

Port 3(Pin 10-17) 

Dual-purpose port-  1. general purpose I/O port.                                  2. pins have alternate purpose related to special features of the 8051                                                Internal pull-ups 

 

The 8051 internal ports are partly bi-directional (Quasi-bi-directional). The following is the internal circuitry for the 8051 port pins:

                                       

1.Configuring for output

P0 is open drain.– Has to be pulled high by external 10K resistors.– Not needed if P0 is used for address lines

Writing to a port pin loads data into a port latch that drives a FET connected to the port pin.

P0: Note that the pull-up is absent on Port 0 except when functioning as the external address/data bus. When a "0" is written to a bit in port 0, the pin is pulled low. But when a "1" is written to it, it is in high impedance (disconnected) state. So when using port 0 for output, an external pull-up resistor is  needed, depending on the input characteristics of the device driven by the port pin P1, P2, P3 have internal pull-ups: When a "0" is written to a bit in these port , the pin is pulled low ( FET-ON) ,also when 1 is written  to a bit in these port pin becomes high (FET-OFF) thus using port P1,P2,P3 is simple.

2. Configuring for input

At power-on all are output ports by defaultTo configure any port for input, write all 1’s (0xFF) to the port     Latch bit=1, FET=OFF, Read Pin asserted by read instruction

You can used a port for output any time. But for input, the FET must be off. Otherwise, you will be reading your own latch rather than the signal coming from the outside. Therefore, a "1" should be written to the pin if you want to use it as input, especially when you have used it for output before. If you don't do this input high voltage will get grounded through FET so you will read pin as low and not as high. An external device cannot easily drive it high

so, you should not tide a port high directly without any resistor. Otherwise, the FET would burn.

Be Careful :

Some port pins serve multiple functions. Be careful writing to such ports. For example, P3.0 is the UART RXD (serial input), and P3.1 is the UART TXD (serial output). If you set P3.0 to a '0', an external buffer (such as an RS232 level translator) cannot drive it high. Therefore you have prevented receiving any serial input.

If an external interrupt such as EX1 on P3.3 is enabled, and set to be level sensitive, and you clear this pin's output latch to a zero, guess what? You've just caused a perpetual interrupt 1. The pin's input buffer will read the output of it's latch as always low. Your controller will spend all of its time in the interrupt handler code and will appear to have crashed, since it will have very little time for other tasks. In fact, it will get to execute a single instruction before re-entering the interrupt handler, so the rest of your program will execute very, very slowly.

Program code

// Program to make a digital clock using LCD

#include<reg51.h>

#define cont_port P3

#define port P1

#define dataport P2 // Data port for LCD

#define m_sec 10

sbit rs = cont_port^0;

sbit rw = cont_port^1;

sbit en = cont_port^6;

sbit dig_hr1=port^0;

sbit dig_min1=port^1;

sbit start=port^2;

sbit am_pm=port^3;

int hr ,hr1=0;

int min,min1=0;

int sec,sec1=0,dig_am_pm=0;

void delay(unsigned int msec) // Time delay funtion

{

int i,j ;

for(i=0;i<msec;i++)

for(j=0;j<1275;j++);

}

void lcd_cmd(unsigned char item) // Function to send command on LCD

{

dataport = item;

rs= 0;

rw=0;

en=1;

delay(1);

en=0;

return;

}

void lcd_data(unsigned char item) // Function to send data on LCD

{

dataport = item;

rs= 1;

rw=0;

en=1;

delay(1);

en=0;

return;

}

void lcd_data_string(unsigned char *str) // Function to send string on LCD

{

int i=0;

while(str[i]!='\0')

{

lcd_data(str[i]);

i++;

delay(1);

}

return;

}

lcd_data_int(int time_val) // Function to send number on LCD

{

int int_amt;

int_amt=time_val/10;

lcd_data(int_amt+48);

int_amt=time_val%10;

lcd_data(int_amt+48);

}

void lcd(unsigned char str1[10]) // Function to initialize LCD

{

lcd_cmd(0x38); //2 LINE, 5X7 MATRIX

lcd_cmd(0x0e); //DISPLAY ON, CURSOR BLINKING

delay(m_sec);

lcd_data_string(str1);

}

void set_hr1() // Function to set hour

{

hr1++;

if(hr1>11)

hr1=0;

lcd_cmd(0xc3);

lcd_data_int(hr1);

lcd_data(':');

}

void set_min1() // Function to set minute

{

min1++;

if(min1>59)

min1=0;

lcd_cmd(0xc6);

lcd_data_int(min1);

}

void main()

{

int k;

start=1;

dig_hr1=1;

dig_min1=1;

lcd_cmd(0x01);

lcd_cmd(0x83);

lcd("SET TIMING");

lcd_cmd(0xc3);

lcd_data_int(hr1);

lcd_data(':');

lcd_data_int(min1);

while(start==0)

{

delay(10);

if(dig_hr1==0)

set_hr1();

if(dig_min1==0)

set_min1();

}

if(am_pm==0)

{

lcd_cmd(0xc8);

  lcd_data_string("am");

  dig_am_pm=0;

}

if(am_pm==1)

{

  lcd_cmd(0xc8);

  lcd_data_string("pm");

  dig_am_pm=1;

}

delay(200);

lcd_cmd(0x01);

while(1)

{

  for(k=0;k<2;k++)

  {

   for(hr=hr1;hr<12;hr++)

   {

    for(min=min1;min<60;min++)

     {

      for(sec=0;sec<60;sec++)

      {

       lcd_cmd(0x82);

       delay(1);

       lcd_data_int(hr);

       lcd_data(':');

       lcd_data_int(min);

       lcd_data(':');

       lcd_data_int(sec);

       if(dig_am_pm==0)

       {

        lcd("am");

       }

       else

       {

        lcd("pm");

       }

       lcd_data_string("    ");

       delay(100);

      }

     }

    min1=0;

    }

  if(dig_am_pm==0)

  dig_am_pm=1;

  else

  dig_am_pm=0;

  hr1=0;

  }

}

}

Overview to Keil compiler

Keil development tools for the 8051 Microcontroller Architecture support every level of software developer from the professional applications engineer to the student just learning about embedded software development.

The industry-standard Keil C Compilers, Macro Assemblers, Debuggers, Real-time Kernels, Single-board Computers, and Emulators support all 8051 derivatives and help you get your projects completed on schedule.

Tool OverviewThe Keil 8051 Development Tools are designed to solve the complex problems facing embedded software developers. When starting a new project, simply select the microcontroller you use from

the Device Database and the µVision IDE sets all compiler, assembler, linker, and memory options for you.

Numerous example programs are included to help you get started with the most popular embedded 8051 devices.

The Keil µVision Debugger accurately simulates on-chip peripherals (I²C, CAN, UART, SPI, Interrupts, I/O Ports, A/D Converter, D/A Converter, and PWM Modules) of your 8051 device. Simulation helps you understand hardware configurations

and avoids time wasted on setup problems. Additionally, with simulation, you can write and test applications before target hardware is available.

When you are ready to begin testing your software application with target hardware, use the MON51, MON390, MONADI, or FlashMON51 Target Monitors, the ISD51 In-System Debugger, or the ULINK USB-JTAG Adapter to download and test program code on your target system

Interfacing to 8051 I/O ports.

 

 

SWITCH ON I/O PORTS 

 

Good CircuitIt is always best connecting the switch to ground with a pull-up resistor as shown in the "Good" circuit. When the switch is open, the 10k resistor supplies very small current needed for logic 1. When it is closed, the port pin is short to ground. The voltage is 0V and all the sinking current requirement is met, so it is logic 0. The 10k resistor will pass 0.5 mA (5 Volt/10k ohm). Thus the circuits waste very little current in either state. The drawback is that the closure of switch gives logic 0 and people like to think of a switch closure gives logic 1. But this is not a matter because it is easy to handle in software. Fair circuitThe "Fair" circuit requires that the pull-down resistor be very small. Otherwise, the pin will rise above 0.9V when the resistor passes the 1.6mA sinking current. When the switch is closed, the circuit waste a large current since virtually no current flows into the pin. The only advantage is that a switch closure gives logic 1. Poor circuitIn the "Poor" circuit, the logic 1 is stable when the switch is closed. But when the switch is open, the input floats to a noise-sensitive high rather than a low. An open TTL pin is usually read as logic 1 but the pin may picks up noise like an antenna.

To conclude, driving a TTL input should always consider current sinking (pulling input to 0V).

 

LED ON I/O PORTS

                                                                                      

Since TTL outputs is designed to feed multiple TTL inputs, they are good at current sinking but poor at current sourcing. The Standard TTL can sink up to 16mA and source 250uA. The LS logic family can sink 8mA and source 100uA. The 8051 port pin can sink 1.6mA (3.2mA for port 0) and source 60uA. Therefore, if you drive significant current, try to arrange your circuits to use current sinking.

Unlike diodes, Light-emitting diodes have a forward voltage drop from 1.7 to 2.5 volts and most of them flow a forward current 20mA.

Poor circuitsince  the TTL output can't source above 1mA so the LED will be very dim. Fair circuitThe LED will conduct heavily at about 2V and the extra 3V has to be dropped in the TTL circuitry. This causes high power dissipation in the TTL or the LED fails. Good circuitThe resistor limits the current. The resistance can be calculated by assuming its voltage is about 2.5V and the TTL output is 0.9V. For 2.2V LED, 1.9V is across the resistor so the 220ohm would limit the current to 8.6mA (1.9/220). For 1.7V LED, 2.4V is across the resistor so it would limit the current to 10.9mA (2.4/220). The resistor should not less than 100ohm or the LED would fail.   

 CODE EXAMPLE Connection -Switch -P1.0 , LED - P2.0  Condition - Turn on LED when switch is pressed. 

ASSEMBLY LANGUAGE C LANGUAGE             (SPJ )

SETB P1.0       ;  input pin.LOOP:

BIT button p1.0  / * Using BIT keyword for p1.0 definition*/BIT LED p2.0

JB P2.0, LOOP  ; not grounded  then stay in loopCLR P0.0 ;To clear pin P0.0 when P1.0 is at 0 v

void main ( )

while (1) {LED = button ; /* Note LED=button is wrong */

 

RELAY ON I/O PORT (2CO Relay)

                                               

In A, NPN transistor  (say a BC337 or BC338) is being used to control a relay with a 5 V coil. Series base resistor R1 is used to set the base current for Q1, so that the transistor is driven into saturation (fully turned on) when the relay is to be energized. That way, the transistor will have minimal voltage drop, and hence dissipate very little power as well as delivering most of the 5V to the relay coil.

How do  work out the value of R1?.  Let us say RLY1 needs 50mA of coil current to pull in and hold reliably, and has a resistance of 24 Ohms so it draws this current from 5V. Our BC337/338 transistor will need enough base current to make sure it remains saturated at this collector current level. To work this out, we simply make sure that the base current is greater than this collector current divided by the transistors minimum DC current gain hFE. So as the BC337/338 has a minimum hFE of 100 (at 100mA), we'll need to provide it with at least 50mA/100 = 0.5mA of base current.In practice, you give it roughly double this value, say 1mA of base current, just to make sure it does saturate. So if your resistance will be  TTL Logic High Voltage (Min) /1ma ( 1K approx) 

  EXAMPLE                                                                 

Connection -Port 0 is connected to eight LEDs, each of them is connected to 5V through a 330ohm resistor. Port 1 is connected to a DIP switch and a 10Kohm resistor

Condition - Corresponding led should light up when switch pressed , i.e.  if Switch at 1.0 is pressed -> LED at P0.0 should light up.

 

ASSEMBLY LANGUAGE   C LANGUAGE             (SPJ SIDE51)

       

LOOP:mov p1,#0ffh ; To configure port for input.mov a,p1mov p0 ,asjmp LOOP  ; Stay in infinite loop  

  .

 

 

 

 

1.

void main() {    while (1) {        P0 = P1; /* Note P1=P0 will not work    }}

2.

voided main() {

    char port_value;    while (1) {        port_value = P1;        P0 = port_value;    }}

CODE EXAMPLE

 

 1 THE CIRCUIT The circuit to be simulated is shown here, consisting of a PIC 16F877 microcontroller unit (MCU), input push buttons and output LEDs which will display a binary count. An external adjustable CR clock circuit is used. The push buttons are not used in the simple program BIN1. Make a folder to hold the project files called BIN1. 

Circuit Schematic

 2 THE SCHEMATIC The ISIS user interface is shown here, consisting of edit, overview and object select windows, with edit toolbars. Components are added to the object list from the libraries provided, dropped onto the schematic, and connected up using virtual wiring. Components can be labelled and their simulation properties modified.  Save the schematic as BIN1.DSN in the project folder. 

ISIS Screen 

  3 SELECT COMPONENTS Components are found in the libraries accessed via the ‘pick’ button P in the object select window. The MCU is selected from ‘Microprocessors ICs’ category, ‘PIC16 Family’ sub-category. The other components are added to the pick list from the appropriate categories. These are then selected and dropped on the schematic within the blue border.  

Component selection dialogue 

Save the design file BIN1.DSN in the project folder.

   4 WRITE PROGRAM The MCU needs a program to work as required. From the ‘Source’ menu, select ‘add source file’, ‘new’ and open the source file BIN1.ASM in folder BIN1. Select code generation tool MPASM. Open the source edit window by selecting the new file from the source menu, and enter the source code listed here. It is a minimal program which produces a binary count at Port B (06). Save the source file code file BIN1.ASM in the project folder.   

Program Source Code   PROCESSOR 16F877  MOVLW 00 TRIS 06  CLRF 06again INCF 06 GOTO again  END

  5 ASSEMBLE PROGRAM Save the source code when complete. From the Source menu, select Build All. The message window should confirm build OK. If not, correct syntax errors in the source code by reference to PIC programming rules. A hex file is produced as shown, BIN1.HEX, which contains the MCU machine code. The machine code program BIN1.HEX is stored automatically in the project folder with the source code. 

Machine Code Program   :020000040000FA:0A000000003066008601860A03281E:00000001FF  

  6 ATTACH PROGRAM This hex file must be attached to the MCU in the schematic. Right click, then left click on the PIC chip to open the Edit Component dialogue. Click on the Program File folder tab and select the BIN1.HEX file from the project folder. Set the Processor Clock Frequency to 40kHz. Note that the external components do not affect the simulation clock frequency. The Port

MCU properties dialogue 

B output LEDs should operate when the run/step/pause/stop controls are clicked (the buttons on the schematic have no effect with this program).  Save the completed design file. 

   7 TEST PROGRAM Pause the program and from the Debug menu check the PIC CPU Source Code option to display the program with the execution point highlighted. Use the ‘Step Into’ button in the source code window to single step the program. Note that the initialisation instructions are executed once, and the loop then repeats endlessly – this is the usual program operating sequence for control applications. The source code window has buttons to run, single step (into, over and out of subroutines) and set breakpoints. Correct any logical program errors detected.

Source code debug window 

   8 DEBUG PROGRAM To monitor program progress, the MCU registers can be displayed, and other changes monitored, using: 

        Special function register display        RAM register display        Register watch window        Execution clock        Simulation logs

 The effect of the program on the registers and status flags, and program timing can thus be checked. Save the test window arrangement using ‘save preferences’. 

Program debug windows 

  

 9 DOWNLOAD PROGRAM When all logical errors have been resolved, the program can be downloaded to the real hardware using the programming tools in MPLAB, for example, using the Mpstart programmer unit. Alternatively, the ICD system allows in-circuit programming and debugging, requiring the purchase of the MPLAB ICD2 module. 

Development System  See www.microchip.com 

 

PC +PROTEUS+ MPLAB

ICDmodule

REFRENCES

www.altavista.comwww.8051.netwww.8051.infowww.freewebs.comwww.innovationrnd.inwww.google.comwww.scribd.comwww.esnips.com