09-11-2012, 05:02 PM
TUTORIAL ON INTERFACING LCD
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The interfacing of LCD is explained using HD44780U as the Dot Matrix Liquid Crystal Display Controller/Driver. HD44780U is a programmable chip for various LCD display control functions. It drives the dot-matrix liquid crystal display. It can be configured under the control of a microprocessor.
In our example, we will connect the LCD controller to the LPC2148 microcontroller. We will use the GPIO pins of LPC2148 for the purpose of connecting the LCD controller. We will then write a program to output some specific values to the GPIO pins (what values to write – we will discuss about them shortly). This program will be executed in the ARM processor of the LPC2148 microcontroller. The LCD controller, on receiving the bits sent over the GPIO pins, will display characters on the LCD and perform other control functions.
Pins in the LCD Controller
1. DB0 to DB7 – the data bus pins. These signals can be used to send 8 bits of data from the microcontroller to the LCD controller or from the LCD controller to the microcontroller. DB7 can be used a busy flag also. More about Bust flag later.
2. The R/W signal selects between a Read and a Write operation. If R/W is equal to 0, a Write operation will be performed. For a Write operation, DB0 to DB7 will be used to send data from the microcontroller to the LCD controller. If R/W is equal to 1, a Read operation will be performed. For a Read operation, DB0 to DB7 will be used to send data from the LCD controller to the microcontroller.
3. Two of the registers available in the LCD controller are the Instruction Register and the Data Register. More about how these registers are used later. The RS signal selects between these two registers. RS equal to 0 selects the Instruction register for a Write operation. This means that if RS=0 and R/W=0, the data sent over DB0 to DB7 will be put in the Instruction register. RS equal to 0 selects the Busy Flag for Read operation. This means that if RS=0 and R/W=1, the value in the Busy Flag will be sent over DB7. RS equal to 1 selects the Data register for Read and Write operation. This means that if RS=1 and R/W=0, the data sent over DB0 to DB7 will be put in the Data register. If RS=1 and R/W=1, the value in the Data register will be sent over DB0 to DB7.
4. The E signal is used to start data read or write. When the data is sent to the data pins of the LCD, a high to low pulse must be applied to the E signal so that the LCD latches the data present at its pins. Similarly a high to low pulse must be provided to the E signal during a Read operation.
[attachment=38820]
The interfacing of LCD is explained using HD44780U as the Dot Matrix Liquid Crystal Display Controller/Driver. HD44780U is a programmable chip for various LCD display control functions. It drives the dot-matrix liquid crystal display. It can be configured under the control of a microprocessor.
In our example, we will connect the LCD controller to the LPC2148 microcontroller. We will use the GPIO pins of LPC2148 for the purpose of connecting the LCD controller. We will then write a program to output some specific values to the GPIO pins (what values to write – we will discuss about them shortly). This program will be executed in the ARM processor of the LPC2148 microcontroller. The LCD controller, on receiving the bits sent over the GPIO pins, will display characters on the LCD and perform other control functions.
Pins in the LCD Controller
1. DB0 to DB7 – the data bus pins. These signals can be used to send 8 bits of data from the microcontroller to the LCD controller or from the LCD controller to the microcontroller. DB7 can be used a busy flag also. More about Bust flag later.
2. The R/W signal selects between a Read and a Write operation. If R/W is equal to 0, a Write operation will be performed. For a Write operation, DB0 to DB7 will be used to send data from the microcontroller to the LCD controller. If R/W is equal to 1, a Read operation will be performed. For a Read operation, DB0 to DB7 will be used to send data from the LCD controller to the microcontroller.
3. Two of the registers available in the LCD controller are the Instruction Register and the Data Register. More about how these registers are used later. The RS signal selects between these two registers. RS equal to 0 selects the Instruction register for a Write operation. This means that if RS=0 and R/W=0, the data sent over DB0 to DB7 will be put in the Instruction register. RS equal to 0 selects the Busy Flag for Read operation. This means that if RS=0 and R/W=1, the value in the Busy Flag will be sent over DB7. RS equal to 1 selects the Data register for Read and Write operation. This means that if RS=1 and R/W=0, the data sent over DB0 to DB7 will be put in the Data register. If RS=1 and R/W=1, the value in the Data register will be sent over DB0 to DB7.
4. The E signal is used to start data read or write. When the data is sent to the data pins of the LCD, a high to low pulse must be applied to the E signal so that the LCD latches the data present at its pins. Similarly a high to low pulse must be provided to the E signal during a Read operation.