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

Fri Aug 29 2014, 12:17 AM
sufiyan
please can you tell me which type of lock activator should i connect in place of LED? can i use selenoid lock actuator
ajay_bhargav
Thu Aug 28 2014, 06:34 AM
Please post questions in forum
Thu Aug 28 2014, 01:44 AM
yednekachew
can you give a project made bay proteus software
Mon Aug 25 2014, 07:12 AM
Vinod Soni
Hi Sir, How can i make this RFID with ATMega16/32 controller
pavanjain
Sat Aug 23 2014, 05:10 AM
Sir i want to download the hex file in P89v51rd2 microcontroller using max232 IC but we not load the program in IC
Tue Aug 19 2014, 04:51 PM
allen ndumu
please i will like to know if the problem of speed control of dc motor using keypad and l298 was if yes can i have the complete project send it to the address i really need to see it
Tue Aug 19 2014, 10:47 AM
Amit Bisht
sir i want to have some trending projects on which i could work related to ATmega 16 microcontroller
ExperimenterUK
Sat Aug 16 2014, 04:16 PM
@diligent . create a thread
Sat Aug 16 2014, 03:17 PM
diligent
in assembly langauage programming..
Sat Aug 16 2014, 03:14 PM
diligent
will anyone help me?

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enisi
Wed Aug 27 2014, 06:08 AM
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Wed Aug 20 2014, 06:28 AM
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Forum Activity
ExperimenterUK Avatar
Posted By ExperimenterUK
Thu Aug 28 2014, 03:31 PM
So, I don't think there is any need to load any da...
ajay_bhargav Avatar
Posted By ajay_bhargav
Thu Aug 28 2014, 06:33 AM
Did your professor ask this question to you? I sug...
siddique Avatar
Posted By siddique
Thu Aug 28 2014, 01:09 AM
hi,In the Tx code, I have disabled auto acknowledg...
ExperimenterUK Avatar
Posted By ExperimenterUK
Wed Aug 27 2014, 04:59 PM
Your board has two serial ports, are you connectin...
ExperimenterUK Avatar
Posted By ExperimenterUK
Wed Aug 27 2014, 04:45 PM
In your TX code I see where you set payload width ...
enisi Avatar
Posted By enisi
Wed Aug 27 2014, 07:05 AM
It can be more than one ansawer correctly
enisi Avatar
Posted By enisi
Wed Aug 27 2014, 06:57 AM
Port 0 is connected indicator 7 segments, so that ...
siddique Avatar
Posted By siddique
Wed Aug 27 2014, 01:48 AM
Pls check the Tx and Rx functions have made some c...
ExperimenterUK Avatar
Posted By ExperimenterUK
Tue Aug 26 2014, 06:03 PM
I assume you have made the changes I suggested to ...
siddique Avatar
Posted By siddique
Tue Aug 26 2014, 03:20 AM
Hi,Tried your suggestions.when i put the device in...