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

Qasim359
Tue Apr 21 2015, 07:31 AM
hello every one i have made pic industrial and domestic timer and i can,t understand c code written in Hi-Tech please send me Mikroc code for this project anyone...................
ExperimenterUK
Wed Apr 15 2015, 05:07 PM
@Bibek.. and everyone. Create threads if you need help. The chat box is just for chat
ExperimenterUK
Wed Apr 15 2015, 05:06 PM
@mohd atif ..login..create a post/thread,then I can post a copy of the missing file
Mon Apr 13 2015, 07:03 PM
mohd atif
@experimenteruk I didn't get you
Sun Apr 12 2015, 04:18 AM
Bibek
hello, i have made a digital clock using rtc DS12887 and AT89S52 with date n callender. Now i want to add alarm features to it.....can any body help me with the code in assembly language
Sun Apr 12 2015, 03:22 AM
SANJU123
Hello, I am planning to do simulaton of the ' 4-way traffic controller'. As a first stage of the project, I tried to compile the code given in this website in keil microvision which controls 4-way traffic . I am using AT89C51. But when I am trying to compile the code it shows an error " Device is not supported by Toolchain". Can u please help me...
Sat Apr 11 2015, 02:06 AM
Suryamoy Mondal
There is a little bit confusion to connect the rs232 connector to max232 ..By continuty test i cant able to find , which wire from the other side of the RS232 connector , i connect to max232..is there any colour coding?
ajay_bhargav
Fri Apr 10 2015, 06:19 PM
@Suryamoy, The PC control software is provided within the package. Follow the steps to install and test it.
Fri Apr 10 2015, 05:24 PM
Suryamoy Mondal
my final year btech project is pc remote control..i have made the hardware and microcontroller prograaming from yours project..bt i cant able to implement in PC..so wht kind of software need for pc to access this..please sir reply me ..i need your help
ExperimenterUK
Wed Apr 08 2015, 04:46 PM
@mohd atif If you create a thread, I may be able help

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Qasim359
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Qasim359 Avatar
Posted By Qasim359
Tue Apr 21 2015, 07:26 AM
i can,t understand C Code written in Hi-Tech pleas...
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Posted By gaurav7577
Mon Apr 20 2015, 07:04 AM
k..let me make all this simple for u so u can add...
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Posted By ajay_bhargav
Sun Apr 19 2015, 06:50 PM
Please zip and attach the code in future. You forg...
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Posted By ajay_bhargav
Sun Apr 19 2015, 06:48 PM
It is really hard to say which course and/or insti...
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Posted By sanju123
Sun Apr 19 2015, 04:56 AM
Thanks rickey...I have reinstalled version.. Pro...
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Posted By lumines
Sun Apr 19 2015, 12:19 AM
Dear everyone,We are currently looking for an embe...
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Posted By gaurav7577
Fri Apr 17 2015, 03:26 PM
thanks ajay for ur concern .....passed out B.E.......
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Posted By ajay_bhargav
Fri Apr 17 2015, 12:49 PM
can you post screenshot or a picture of CRO output...
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Posted By ajay_bhargav
Fri Apr 17 2015, 12:45 PM
are you in a college or working?