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

Sun Sep 25 2016, 04:41 AM
mira
hi sir, could you help me regarding simple multiplication calculator?it should be include with buzzer. i use dragonplus. please
ExperimenterUK
Sat Sep 24 2016, 05:49 PM
@Rus Ans .. what project ?
ExperimenterUK
Sat Sep 24 2016, 05:48 PM
@engr1931 depends on type of scanner
engr1931
Sat Sep 24 2016, 03:07 PM
Is it possible to send data from 2 barcode scanner to pc using serial port using 8051?
Wed Sep 21 2016, 02:22 AM
Rus Ana
can anyone help me for my project? T.T
Fri Sep 09 2016, 02:54 PM
Sarath babu
8051 a/c motor speed control
Tue Aug 30 2016, 05:03 PM
Kinzang
hello sir, can i know more in detail about the football substitution board project.
Tue Aug 30 2016, 06:06 AM
bhagyashri buddhewad
my project is automatic room light controller using visitor counter so i want coding in keil and circuit diagram can tell me and i want to use uc at89c51 thanks you
ExperimenterUK
Sun Aug 28 2016, 08:32 PM
Which project ?
Sun Aug 28 2016, 05:21 AM
Dipankar Baishya
Hi sir.... I want do this project but I have not this sercuit diagram..... can you give me full details and diagram...... Thank you

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ak_pan
Thu Sep 08 2016, 06:28 PM
martinsnc115877
Sat Aug 20 2016, 01:44 PM
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CASINODIGITAL
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mariahcarey
Sat Aug 06 2016, 11:38 AM
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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...
rajavarmanslr Avatar
Posted By rajavarmanslr
Thu Aug 18 2016, 01:40 PM
I have two 8051 that interfaces with nRF24l01. One...
rajavarmanslr Avatar
Posted By rajavarmanslr
Thu Aug 18 2016, 12:31 PM
I have two 8051 that interfaces with nRF24l01. One...
ExperimenterUK Avatar
Posted By ExperimenterUK
Mon Aug 01 2016, 05:26 AM
is working nowugoo5000Great, thanks for letting u...
ugoo5000 Avatar
Posted By ugoo5000
Sat Jul 30 2016, 07:31 AM
is working noworg 00hmov p1,#11111111bmov p3,#1111...
ugoo5000 Avatar
Posted By ugoo5000
Sat Jul 30 2016, 06:40 AM
when i press a button in p3.0,the counter will st...
ugoo5000 Avatar
Posted By ugoo5000
Sat Jul 30 2016, 06:30 AM
proteus file Attachment ...
ExperimenterUK Avatar
Posted By ExperimenterUK
Fri Jul 29 2016, 11:34 PM
Your code does not count at all, it produces a one...
ugoo5000 Avatar
Posted By ugoo5000
Fri Jul 29 2016, 07:49 PM
i want the the counter to be counting in secs with...