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Showing posts with label microcontroller. Show all posts
Showing posts with label microcontroller. Show all posts
Simple Digital clock using 8051 microcontroller (AT89C51)
A digital clock is one that displays time digitally. The circuit explained here displays time with two ‘minutes’ digits and two ‘seconds’ digits on four seven segment displays. The seven segment and switches are interfaced with 8051 microcontroller AT89C51. This circuit can be used in cars, houses, offices etc.
DESCRIPTION :
How to interface 16x2 LCD with 8051 microcontroller (AT89C51)
It is very important to keep a track of the working of almost all the automated and semi-automated devices, be it a washing machine, an autonomous robot or anything else. This is achieved by displaying their status on a small display module. LCD (Liquid Crystal Display) screen is such a display module and a 16x2 LCD module is very commonly used. These modules are replacing seven segments and other multi segment LEDs for these purposes. The reasons being: LCDs are economical, easily programmable, have no limitation of displaying special & even custom characters (unlike in seven segments), animationsand so on. LCD can be easily interfaced with a microcontroller to display a message or status of a device. This topic explains the basics of a 16x2 LCD and how it can be interfaced with AT89C51 to display a character
DESCRIPTION :
A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers.
1. Command/Instruction Register - stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing, clearing the screen, setting the cursor position, controlling display etc.
2. Data Register - stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD.
Commonly used LCD Command codes:
Hex Code
|
Command to LCD Instruction Register
|
1
|
Clear screen display
|
2
|
Return home
|
4
|
Decrement cursor
|
6
|
Increment cursor
|
E
|
Display ON, Cursor ON
|
80
|
Force the cursor to the beginning of the 1st line
|
C0
|
Force cursor to the beginning of the 2nd line
|
38
|
Use 2 lines and 5x7 matrix
|
The pin description of this module is given below.
Pin configuration:
Pin
|
Symbol
|
Description
| |
1
|
VSS
|
Ground
|
0 V
|
2
|
VCC
|
Main power supply
|
+5 V
|
3
|
VEE
|
Power supply to control contrast
|
Contrast adjustment by providing a variable resistor through VCC
|
4
|
RS
|
Register Select
|
RS=0 to select Command Register
RS=1 to select Data Register
|
5
|
R/W
|
Read/write
|
R/W=0 to write to the register
R/W=1 to read from the register
|
6
|
EN
|
Enable
|
A high to low pulse (minimum 450ns wide) is given when data is sent to data pins
|
7
|
DB0
|
To display letters or numbers, their ASCII codes are sent to data pins (with RS=1). Also instruction command codes are sent to these pins.
| |
8
|
DB1
| ||
9
|
DB2
| ||
10
|
DB3
|
8-bit data pins
| |
11
|
DB4
| ||
12
|
DB5
| ||
13
|
DB6
| ||
14
|
DB7
| ||
15
|
Led+
|
Backlight VCC
|
+5 V
|
16
|
Led-
|
Backlight Ground
|
0 V
|
Programming the LCD:
1. Data pin8 (DB7) of the LCD is busy flag and is read when R/W = 1 & RS = 0. When busy flag=1, it means that LCD is not ready to accept data since it is busy with the internal operations. Therefore before passing any data to LCD, its command register should be read and busy flag should be checked.
2. To send data on the LCD, data is first written to the data pins with R/W = 0 (to specify the write operation) and RS = 1 (to select the data register). A high to low pulse is given at EN pin when data is sent. Each write operation is performed on the positive edge of the Enable signal.
3. To send a command on the LCD, a particular command is first specified to the data pins with R/W = 0 (to specify the write operation) and RS = 0 (to select the command register). A high to low pulse is given at EN pin when data is sent.
Displaying single character ‘A’ on LCD
The LCD is interfaced with microcontroller (AT89C51). This microcontroller has 40 pins with four 8-bit ports (P0, P1, P2, and P3). Here P1 is used as output port which is connected to data pins of the LCD. The control pins (pin 4-6) are controlled by pins 2-4 of P0 port. Pin 3 is connected to a preset of 10k? to adjust the contrast on LCD screen. This program uses the above concepts of interfacing the LCD with controller by displaying the character ‘A’ on it
CIRCUIT DIAGRAM :
VIDEO ;
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