INITIALIZING THE LCD
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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:
SETB EN
CLR RS
MOV DATA,#38h
CLR EN
LCALL WAIT_LCD
Programming Tip: The LCD command 38h is really the sum of a number of option bits. The instruction itself is the instruction 20h ("Function set"). However, to this we add the values 10h to indicate an 8-bit data bus plus 08h to indicate that the display is a two-line display.
We've now sent the first byte of the initialization sequence. The second byte of the initialization sequence is the instruction 0Eh. Thus we must repeat the initialization code from above, but now with the instruction. Thus the next code segment is:
SETB EN
CLR RS
MOV DATA,#0Eh
CLR EN
LCALL WAIT_LCD
Programming Tip: The command 0Eh is really the instruction 08h plus 04h to turn the LCD on. To that an additional 02h is added in order to turn the cursor on.
The last byte we need to send is used to configure additional operational parameters of the LCD. We must send the value 06h.
SETB EN
CLR RS
MOV DATA,#06h
CLR EN
LCALL WAIT_LCD
Programming Tip: The command 06h is really the instruction 04h plus 02h to configure the LCD such that every time we send it a character, the cursor position automatically moves to the right.
So, in all, our initialization code is as follows:
INIT_LCD:
SETB EN
CLR RS
MOV DATA,#38h
CLR EN
LCALL WAIT_LCD
SETB EN
CLR RS
MOV DATA,#0Eh
CLR EN
LCALL WAIT_LCD
SETB EN
CLR RS
MOV DATA,#06h
CLR EN
LCALL WAIT_LCD
RET
Having executed this code the LCD will be fully initialized and ready for us to send display data to it.
