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.

Share it! Like it!

Conversation

ExperimenterUK
Tue Jul 19 2016, 05:59 PM
@mhammad 64 bits is 8 bytes.
Tue Jul 19 2016, 07:56 AM
mhammad kassem
hello! i want to know how to use UART in mikroc , I want to receive 64 bits from another microcontroller and i dont know how to start my code to receive the 64 bits...any help?
ExperimenterUK
Mon Jul 18 2016, 08:32 PM
@meena.. are you still having trouble ?
Sat Jul 16 2016, 10:19 AM
Meena
problem in loading email address while registering.Please help
Sun Jul 10 2016, 02:50 PM
shockwave
could you please provide a sample code that controling LED using bluetooth HC-05 interfacing pic16f877a thank you!
Sun Jul 10 2016, 02:49 PM
shockwave
Help!
ExperimenterUK
Sat Jul 09 2016, 05:25 PM
@Santhana krishnan post in forum to discuss your problem
Thu Jul 07 2016, 09:26 AM
Santhana krishnan
Hi i program atmega 32 it was functiining corectly but now aref pins voltage 2.56 is droped to .85 volts also a ports input viltage also dropped so anologe inpit not funcitonig please help me to find out the problem
Thu Jul 07 2016, 09:24 AM
Santhana krishnan
Hi i program the atmega 32
Thu Jul 07 2016, 09:24 AM
Santhana krishnan
Hi

Downloads

Comments

adithyapaip
Thu Jul 21 2016, 05:45 PM
celu
Thu Jul 21 2016, 05:27 PM
Aiko
Wed Jul 20 2016, 01:51 PM
JorgeG
Sat Jul 16 2016, 07:19 PM
Piotrekk
Wed Jul 06 2016, 09:35 AM
dyoussef
Wed Jun 29 2016, 07:29 PM
sung7333
Tue Jun 28 2016, 06:23 AM
Bonolai
Fri Jun 24 2016, 06:02 AM

Online

Guests: 48, Members: 0 ...

most ever online: 182184
(Members: , Guests: 182184) on 06 Aug 2010: 05:37 AM

Members: 37775
Newest member: adithyapaip
Forum Activity
ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Jul 23 2016, 07:14 PM
I found this datasheet, it is a type of driver.It ...
Piotrekk Avatar
Posted By Piotrekk
Fri Jul 22 2016, 10:12 AM
I found an old box of electronic components in the...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Jul 21 2016, 07:37 PM
That is curious, but very likely a co-incidence.Th...
adithyapaip Avatar
Posted By adithyapaip
Thu Jul 21 2016, 07:18 PM
I am using keil to do everthing in 8051,when I was...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Jul 21 2016, 07:14 PM
By far the easiest and cheapest way to talk to the...
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Jul 21 2016, 07:04 PM
The crystal on the programmer does not affect the ...
adithyapaip Avatar
Posted By adithyapaip
Thu Jul 21 2016, 06:06 PM
Hi Guys..i have a 8051 programmer which has 4mhz c...
Aiko Avatar
Posted By Aiko
Wed Jul 20 2016, 01:56 PM
ankitbajaj01 Avatar
Posted By ankitbajaj01
Wed Jul 20 2016, 04:49 AM
Dear All,Greetings!!!I want to develop Online moni...
sairfan1 Avatar
Posted By sairfan1
Tue Jul 19 2016, 09:56 PM
Now a days there are many smart locks available li...