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

Tue Nov 29 2016, 02:49 PM
jaykumar
Dear sir, elevator microprocessor control , the vendor locked the control, pls help me how can we decode the password
Sat Nov 26 2016, 10:24 AM
manikanta B
hello i know about gsm,gps and zigbee but i dont know how to use them while programming. can anyone suggest me how to use them
ExperimenterUK
Sat Nov 19 2016, 07:09 PM
@Protaz.. Really you would be better off asking on one of the many Arduino user sites
Fri Nov 18 2016, 05:39 AM
Protaz
Hi, am new in programing, but I have few skills in electronic. I want to make an automatic timing system for institutions using arduino uno. Any one to assist me how to program the microcontoller?
Tue Nov 15 2016, 04:45 AM
Hemangi patel
hello, i am working on atmega128 board and i want to interface with sd card with using fat32 file system. i am totaly new in this field .so pls anyone can u suggest me some imp links.thanks
Thu Nov 10 2016, 01:40 PM
ajith raj
hi frds i make voice control robot using blutooth module
Wed Oct 26 2016, 08:23 AM
ishalt
is it possible to completly get the robot running from java code
Sun Oct 23 2016, 05:50 PM
mamata thakur
plz send full mini project report for ic 741&ic 555 tester
Wed Oct 19 2016, 03:30 PM
riddhi1296
can you provide an explanation for the inverter 8051 code and how it works
ExperimenterUK
Sat Oct 15 2016, 12:15 AM
@snaya. Create a thread in the 8051 forum for your questions

Downloads

Comments

Jonathan.kei
Mon Nov 21 2016, 04:30 PM
AVRuser1
Sun Nov 20 2016, 06:07 PM
JaguarPaw
Thu Nov 17 2016, 07:44 PM
PeterJohn
Mon Nov 14 2016, 05:54 PM
evigna
Wed Nov 02 2016, 02:03 PM
ozancakiroglu
Thu Oct 27 2016, 01:54 PM
[email protected]
Fri Oct 21 2016, 10:35 PM
Beliwars
Sat Oct 15 2016, 09:40 AM

Online

Guests: 50, Members: 0 ...

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

Members: 37792
Newest member: Jonathan.kei
Forum Activity
Centurio Avatar
Posted By Centurio
Mon Nov 28 2016, 08:46 AM
Hi there,long time ago... i've a short question to...
kirangowle Avatar
Posted By kirangowle
Wed Nov 16 2016, 03:56 PM
Hello Forum members,After a long time i am back to...
Pratik_Suthar Avatar
Posted By Pratik_Suthar
Thu Oct 13 2016, 12:39 PM
@martin the HEX file provided in the project is no...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Oct 06 2016, 06:15 AM
Hi Phil, Do you want to add this to existing proje...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Oct 06 2016, 06:13 AM
CE should be high when you go for reading mode/wai...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Oct 06 2016, 06:03 AM
You can also use ESP8266 with its SDK to write app...
ExperimenterUK Avatar
Posted By ExperimenterUK
Mon Oct 03 2016, 11:15 PM
This is an old thread and the links no longer work...
martinsnc115877 Avatar
Posted By martinsnc115877
Wed Sep 14 2016, 12:51 PM
sir, i did your led scrolling mass display, and it...
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri Sep 09 2016, 11:45 PM
The Hex file for this project is a bit too big for...