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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Wed Oct 19 2016, 03:30 PM
can you provide an explanation for the inverter 8051 code and how it works
Sat Oct 15 2016, 12:15 AM
@snaya. Create a thread in the 8051 forum for your questions
Fri Oct 14 2016, 10:00 AM
i m going to make a project with 8051and the name is scrolling led message display .now i wanna ask so many of questions.may be u can help me .so help me out
Fri Sep 30 2016, 10:40 AM
plz I want code for adc interfacing with8051
Sun Sep 25 2016, 04:41 AM
hi sir, could you help me regarding simple multiplication calculator?it should be include with buzzer. i use dragonplus. please
Sat Sep 24 2016, 05:49 PM
@Rus Ans .. what project ?
Sat Sep 24 2016, 05:48 PM
@engr1931 depends on type of scanner
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



[email protected]
Fri Oct 21 2016, 10:35 PM
Sat Oct 15 2016, 09:40 AM
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Thu Sep 29 2016, 06:31 AM
Thu Sep 08 2016, 06:28 PM
Sat Aug 20 2016, 01:44 PM
Thu Aug 18 2016, 12:24 PM
Forum Activity
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...
rajavarmanslr Avatar
Posted By rajavarmanslr
Thu Aug 18 2016, 01:40 PM
I have two 8051 that interfaces with nRF24l01. One...