15-06-2012, 11:03 AM
Interfacing an LCD to 8051 Microcontroller :: LCD Programming
[attachment=24512]
Introduction to LCD Programming
SUMMARY
This tutorial has presented the underlying concepts of programming an LCD display. Obviously it has not addresses all issues. The 44780 LCD controller offers many other functions which are accessed using other commands, and some of the commands already presented include other options that were not discussed here. However, this tutorial should get you going in the right direction.
LCD Backgorund
Frequently, an 8051 program must interact with the outside world using input and output devices that communicate directly with a human being. One of the most common devices attached to an 8051 is an LCD display. Some of the most common LCDs connected to the 8051 are 16x2 and 20x2 displays. This means 16 characters per line by 2 lines and 20 characters per line by 2 lines, respectively.
Fortunately, a very popular standard exists which allows us to communicate with the vast majority of LCDs regardless of their manufacturer. The standard is referred to as HD44780U, which refers to the controller chip which receives data from an external source (in this case, the 8051) and communicates directly with the LCD.
AN EXAMPLE HARDWARE CONFIGURATION
As we've mentioned, the LCD requires either 8 or 11 I/O lines to communicate with. For the sake of this tutorial, we are going to use an 8-bit data bus--so we'll be using 11 of the 8051's I/O pins to interface with the LCD.
Let's draw a sample psuedo-schematic of how the LCD will be connected to the 8051.
HANDLING THE EN CONTROL LINE
As we mentioned above, the EN line is used to tell the LCD that you are ready for it to execute an instruction that you've prepared on the data bus and on the other control lines. Note that the EN line must be raised/lowered before/after each instruction sent to the LCD regardless of whether that instruction is read or write, text or instruction. In short, you must always manipulate EN when communicating with the LCD. EN is the LCD's way of knowing that you are talking to it. If you don't raise/lower EN, the LCD doesn't know you're talking to it on the other lines.
Thus, before we interact in any way with the LCD we will always bring the EN line low with the following instruction.
INITIALIZING THE LCD
Before you may really use the LCD, you must initialize and configure it. This is accomplished by sending a number of initialization instructions to the LCD.
The first instruction we send must tell the LCD whether we'll be communicating with it with an 8-bit or 4-bit data bus. We also select a 5x8 dot character font. These two options are selected by sending the command 38h to the LCD as a command. As you will recall from the last section, we mentioned that the RS line must be low if we are sending a command to the LCD. Thus, to send this 38h command to the LCD we must execute the following 8051 instructions.
[attachment=24512]
Introduction to LCD Programming
SUMMARY
This tutorial has presented the underlying concepts of programming an LCD display. Obviously it has not addresses all issues. The 44780 LCD controller offers many other functions which are accessed using other commands, and some of the commands already presented include other options that were not discussed here. However, this tutorial should get you going in the right direction.
LCD Backgorund
Frequently, an 8051 program must interact with the outside world using input and output devices that communicate directly with a human being. One of the most common devices attached to an 8051 is an LCD display. Some of the most common LCDs connected to the 8051 are 16x2 and 20x2 displays. This means 16 characters per line by 2 lines and 20 characters per line by 2 lines, respectively.
Fortunately, a very popular standard exists which allows us to communicate with the vast majority of LCDs regardless of their manufacturer. The standard is referred to as HD44780U, which refers to the controller chip which receives data from an external source (in this case, the 8051) and communicates directly with the LCD.
AN EXAMPLE HARDWARE CONFIGURATION
As we've mentioned, the LCD requires either 8 or 11 I/O lines to communicate with. For the sake of this tutorial, we are going to use an 8-bit data bus--so we'll be using 11 of the 8051's I/O pins to interface with the LCD.
Let's draw a sample psuedo-schematic of how the LCD will be connected to the 8051.
HANDLING THE EN CONTROL LINE
As we mentioned above, the EN line is used to tell the LCD that you are ready for it to execute an instruction that you've prepared on the data bus and on the other control lines. Note that the EN line must be raised/lowered before/after each instruction sent to the LCD regardless of whether that instruction is read or write, text or instruction. In short, you must always manipulate EN when communicating with the LCD. EN is the LCD's way of knowing that you are talking to it. If you don't raise/lower EN, the LCD doesn't know you're talking to it on the other lines.
Thus, before we interact in any way with the LCD we will always bring the EN line low with the following instruction.
INITIALIZING THE LCD
Before you may really use the LCD, you must initialize and configure it. This is accomplished by sending a number of initialization instructions to the LCD.
The first instruction we send must tell the LCD whether we'll be communicating with it with an 8-bit or 4-bit data bus. We also select a 5x8 dot character font. These two options are selected by sending the command 38h to the LCD as a command. As you will recall from the last section, we mentioned that the RS line must be low if we are sending a command to the LCD. Thus, to send this 38h command to the LCD we must execute the following 8051 instructions.