Introduction to 4-bit Mode

Till now whatever we discussed in the previous part of ths LCD tutorial, we were dealing with 8-bit mode. Now we are going to learn how to use LCD in 4-bit mode. There are many reasons why sometime we prefer to use LCD in 4-bit mode instead of 8-bit. One basic reason is lesser number of pins are needed to interface LCD.

In 4-bit mode the data is sent in nibbles, first we send the higher nibble and then the lower nibble. To enable the 4-bit mode of LCD, we need to follow special sequence of initialization that tells the LCD controller that user has selected 4-bit mode of operation. We call this special sequence as resetting the LCD. Following is the reset sequence of LCD.
  1. Wait for abour 20mS
  2. Send the first init value (0x30)
  3. Wait for about 10mS
  4. Send second init value (0x30)
  5. Wait for about 1mS
  6. Send third init value (0x30)
  7. Wait for 1mS
  8. Select bus width (0x30 - for 8-bit and 0x20 for 4-bit)
  9. Wait for 1mS

The busy flag will only be valid after the above reset sequence. Usually we do not use busy flag in 4-bit mode as we have to write code for reading two nibbles from the LCD. Instead we simply put a certain ammount of delay usually 300 to 600uS. This delay might vary depending on the LCD you are using, as you might have a different crystal frequency on which LCD controller is running. So it actually depends on the LCD module you are using. So if you feel any problem running the LCD, simply try to increase the delay. This usually works. For me about 400uS works perfect.

LCD connections in 4-bit Mode




Above is the connection diagram of LCD in 4-bit mode, where we only need 6 pins to interface an LCD. D4-D7 are the data pins connection and Enable and Register select are for LCD control pins. We are not using Read/Write (RW) Pin of the LCD, as we are only writing on the LCD so we have made it grounded permanently. If you want to use it.. then you may connect it on your controller but that will only increase another pin and does not make any big difference. Potentiometer RV1 is used to control the LCD contrast. The unwanted data pins of LCD i.e. D0-D3 are connected to ground.

LCD connections in 4-bit Mode

We will now look into the common steps to send data/command to LCD when working in 4-bit mode. As i already explained in 4-bit mode data is sent nibble by nibble, first we send higher nibble and then lower nibble. This means in both command and data sending function we need to saperate the higher 4-bits and lower 4-bits.


The common steps are:
  1. Mask lower 4-bits
  2. Send to the LCD port
  3. Send enable signal
  4. Mask higher 4-bits
  5. Send to LCD port
  6. Send enable signal

We are done with the theory part now, In the next section we will take a look at the programming microcontroller to control LCD in 4-bit mode.

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Conversation

Mon Mar 27 2017, 04:09 AM
priyanja awate
my project is greenhouse monitering and controlling using 8051 .can u give me the program of this project
ExperimenterUK
Sat Mar 25 2017, 09:56 PM
@Noreen I suggest you log in and post a full description of what you need in our PIC forum
Sat Mar 25 2017, 03:10 PM
Noreen
Hello I worked on a project related to Wireless Electricity theft detection using GSM during my bachelors. I used Nokia 6230 for sending sms using AT commands. I chose to work with SMS text mode. The microcontroller I used was PIC16F877A and its software coding done through PIC Basic Pro. Unfortunately, I lost my account password and do not have coding for generation sms using AT commands. I need that coding. Can some one help me to provide complete Pic Basic Pro code. In which step by step guidance is given so that I can understand easily. Regards,
Wed Mar 22 2017, 09:13 PM
ajay kumar
help me nokia lcd light
Wed Feb 22 2017, 06:14 AM
ChollyMo
Indeed, on the LCD tutorial, many missing Tables and figures !!
Wed Feb 22 2017, 06:06 AM
ChollyMo
I don't see any Table 3. I'm using Chrome.
Fri Feb 03 2017, 05:56 AM
irfan shaikh
hi, i want interface WS2811 pixel led using NUVOTON N79E352, but i dont know how to code it. can anyone help me or provide me sample coding for interfacing WS2811 PIXEL LED. THNX
Thu Jan 19 2017, 08:42 PM
abhays
Hi...i have made a circuit for interfacing PT100 with LM358 whose temperature is shown on the LCD...But the temperature is not getting incresed slowly ..a small change directly increses the temp...can any one help me
Thu Jan 19 2017, 04:27 PM
roba
send me alarm clock simulation using proteus software
Mon Jan 16 2017, 03:15 PM
Rutuja
How can we read notepad file using random acess file

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SAUnwin
Tue Mar 21 2017, 02:29 PM
letonarolikah
Mon Mar 20 2017, 11:21 AM
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XuZiling
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Thu Feb 16 2017, 02:40 PM
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ExperimenterUK Avatar
Posted By ExperimenterUK
Sat Mar 25 2017, 09:49 PM
I have attached code showing one method you could ...
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Posted By Deepakvaishu
Sat Mar 25 2017, 07:59 AM
I am using Keil and 8051 microcontroller
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Posted By ExperimenterUK
Fri Mar 24 2017, 06:05 PM
The best way is to use an interrupt to run the cou...
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Posted By Deepakvaishu
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Hi,I got that we should use timer......But I am a ...
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Thu Mar 23 2017, 09:14 PM
You have largely answered your own question.Use on...
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Thu Mar 23 2017, 07:03 AM
I have looked at your code.I think you are confuse...
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hello,I can type the letters now when the particul...
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HI,There are two ways I'd tackle thiss.Key down on...
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hello,I am using a keypad to type the text message...
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hi.. the following code is not working on hardware...