LCD Initialization

Before using the LCD for display purpose, LCD has to be initialized either by the internal reset circuit or sending set of commands to initialize the LCD. It is the user who has to decide whether an LCD has to be initialized by instructions or by internal reset circuit. we will dicuss both ways of initialization one by one.
Initialization by internal Reset Circuit
An internal reset circuit automatically initializes the HD44780U when the power is turned on. The following instructions are executed during the initialization. The busy flag (BF) is kept in the busy state until the initialization ends (BF = 1). The busy state lasts for 10 ms after VCC rises to 4.5 V.
  • Display clear
  • Function set:
    DL = 1; 8-bit interface data
    N = 0; 1-line display
    F = 0; 5 x 8 dot character font
  • Display on/off control:
    D = 0; Display off
    C = 0; Cursor off
    B = 0; Blinking off
  • Entry mode set:
    I/D = 1; Increment by 1
    S = 0; No shift


Note: If the electrical characteristics conditions listed under the table Power Supply Conditions Using Internal Reset Circuit are not met, the internal reset circuit will not operate normally and will fail to initialize the HD44780U. For such a case, initial-ization must be performed by the MCU as explained in the section, Initializing by Instruction.

As mentioned in the Note, there are certain condtions that has to be met, if user want to use initialization by internal reset circuit. These conditions are shown in the Table 5 below.


Table 5: Power Supply condition for Internal Reset circuit

Figure 7 shows the test condition which are to be met for internal reset circuit to be active.


Figure 7: Internal Power Supply reset



Now the problem with the internal reset circuit is, it is highly dependent on power supply, to meet this critical power supply conditions is not hard but are difficult to achive when you are making a simple application. So usually the second menthod i.e. Initialization by instruction is used and is recommended most of the time.

Initialization by instructions
Initializing LCD with instructions is really simple. Given below is a flowchart that describles the step to follow, to initialize the LCD.


Figure 8: Flow chart for LCD initialization



As you can see from the flow chart, the LCD is initialized in the following sequence...

  1. Send command 0x30 - Using 8-bit interface
  2. Delay 20ms
  3. Send command 0x30 - 8-bit interface
  4. Delay 20ms
  5. Send command 0x30 - 8-bit interface
  6. Delay 20ms
  7. Send Function set - see Table 4 for more information
  8. Display Clear command
  9. Set entry mode command - explained below

The first 3 commands are usually not required but are recomended when you are using 4-bit interface. So you can program the LCD starting from step 7 when working with 8-bit interface. Function set command depends on what kind of LCD you are using and what kind of interface you are using (see Table 4 in LCD Command section).
LCD Entry mode:
From Table 3 in command section, you can see that the two bits decide the entry mode for LCD, these bits are:
a) I/D - Increment/Decrement bit
b) S - Display shift.
With these two bits we get four combinations of entry mode which are 0x04,0x05,0x06,0x07 (see table 3 in LCD Command section). So we get different results with these different entry modes. Normally entry mode 0x06 is used which is No shift and auto incremement. I recommend you to try all the possible entry modes and see the results, I am sure you will be surprised.

Programming example for LCD Initialization
LCD_data equ P2    ;LCD Data port
LCD_D7   equ P2.7  ;LCD D7/Busy Flag
LCD_rs   equ P1.0  ;LCD Register Select
LCD_rw   equ P1.1  ;LCD Read/Write
LCD_en   equ P1.2  ;LCD Enable

LCD_init:
         mov   LCD_data,#38H  ;Function set: 2 Line, 8-bit, 5x7 dots
         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
         mov   LCD_data,#0FH  ;Display on, Curson blinking command
         clr   LCD_rs         ;Selected instruction 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
         mov   LCD_data,#01H  ;Clear LCD

         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
         mov   LCD_data,#06H  ;Entry mode, auto increment with no shift
         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 routine

Now we can do the same thing in C, I am giving example using Keil C. Similar code can be written for SDCC.

#include <AT89X51.H>
.
#define LCD_data P2
#define LCD_D7   P2_7
#define LCD_rs   P1_0
#define LCD_rw   P1_1
#define LCD_en   P1_2

void LCD_init()
{
     LCD_data = 0x38;     //Function set: 2 Line, 8-bit, 5x7 dots
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->
L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
     LCD_data = 0x0F;     //Display on, Curson blinking command
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->
L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
     LCD_data = 0x01;     //Clear LCD
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->
L
     LCD_en   = 0;
     LCD_busy();          //Wait for LCD to process the command
     LCD_data = 0x06;     //Entry mode, auto increment with no shift
     LCD_rs   = 0;        //Selected command register
     LCD_rw   = 0;        //We are writing in data register
     LCD_en   = 1;        //Enable H->
L
     LCD_busy();

}

With the help of the above code, you are able to initialize the LCD. Now there is a function/subroutine coming in the code i.e. LCD_busy, which is used to put delay for LCD so that there should not be any command or data sent to the LCD untill it finish executing the command. More on this delay routine is explained in the next section.

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ExperimenterUK
Wed May 25 2016, 05:05 AM
@ Ramanjaneyulu, post in forum,explain your problem
Mon May 23 2016, 11:34 PM
Ramanjaneyulu
Hi, I Am using at89c4051 for my application, I want 5u sec dely.. Up to 1milli sec iam able to producing delay. Beyond the 1milli second, I am unable to produce the acceurate dely. Plz any one help me
Sat May 21 2016, 09:51 PM
A K
i want to mak an auto dialer using gsm and atmega 16. please helpe me how to write a code to auto dial a number saved in sim
Sat May 21 2016, 10:42 AM
Alec
Hi im trying to program my 89s51 with a usbasp so any ideas on the circuit?
Wed May 18 2016, 10:08 AM
Tashu joshi
anyone know how to develop
Wed May 18 2016, 10:07 AM
Tashu joshi
i'm working for resporatry system using 8051,
Wed May 18 2016, 10:06 AM
Tashu joshi
i'm developing a respiratory system using Arduino
Fri May 13 2016, 11:03 AM
MEGHANA
i need c code for counting frequency of two sensors and compare these frequencies and it has to give high/ low signal after comparision
ExperimenterUK
Tue May 10 2016, 05:02 PM
@Suren ..create a thread in the 8051 Discussion Forum to discuss your problem
Tue May 10 2016, 04:04 PM
Suren Avushyan
how can I increment address not the content of it, like 0x70 and get 0x71

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zaft93
Sun May 15 2016, 01:52 AM
CELEBI
Thu May 12 2016, 08:28 AM
Suro1996
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ExperimenterUK Avatar
Posted By ExperimenterUK
Sun May 15 2016, 10:58 PM
zaft93 Avatar
Posted By zaft93
Sun May 15 2016, 01:55 AM
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Posted By ExperimenterUK
Fri May 13 2016, 07:59 PM
If you want only one relay to be on at a time the ...
CELEBI Avatar
Posted By CELEBI
Fri May 13 2016, 06:16 AM
Yes. It must be as you said. It must be 1.5 second...
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Posted By ExperimenterUK
Thu May 12 2016, 08:35 PM
Here is one way.If you have the Keil compiler you ...
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Posted By ExperimenterUK
Thu May 12 2016, 05:20 PM
Sorry I don't understand what you want.Is that 1.5...
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Posted By CELEBI
Thu May 12 2016, 08:53 AM
Hello Guys, I want to make a Project with 89s51 bu...
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Posted By ExperimenterUK
Wed May 11 2016, 09:28 PM
No this is all I've got, the algorithm I think is ...
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Posted By Suro1996
Wed May 11 2016, 09:27 PM
Is this all the code you have ?As it is, it will n...
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Posted By Suro1996
Wed May 11 2016, 07:31 PM
Hello, I am new to assembly programming and I am h...