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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ajay_bhargav
Mon Mar 23 2015, 04:22 AM
You can only simulate simple 8051. RD2 support is not there in proteus. However there are similar atmel varient which can be used instead.
Sun Mar 22 2015, 07:24 PM
Aryan Nath
How can i Simulate microcontroller project in Proteus that uses P89V51RD2
Thu Mar 19 2015, 02:45 PM
Peter Mann
I have tried to register on the site, but it keeps saying I've entered two different email adresses - but I haven't!
ajay_bhargav
Sun Mar 15 2015, 08:25 PM
I did not get new message indication.. strange..
ExperimenterUK
Sun Mar 15 2015, 08:18 PM
slight delay, my connection failed
ajay_bhargav
Sun Mar 15 2015, 08:08 PM
Atleast you chat on our website if not anywhere else
ajay_bhargav
Sun Mar 15 2015, 08:08 PM
Hi Phil..
ExperimenterUK
Sun Mar 15 2015, 08:05 PM
Hi Ajay
gsdvprasad
Fri Mar 13 2015, 04:20 PM
Can you help me how to change the text on led display in proteus simulation?
ajay_bhargav
Sat Mar 07 2015, 07:48 AM
@Shoukat, its general purpose PCB board for soldering components

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harix
Sun Mar 29 2015, 07:11 PM
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iamalien Avatar
Posted By iamalien
Sun Mar 29 2015, 07:46 PM
yes either that or use the flash reprogrammable va...
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Posted By ajay_bhargav
Sun Mar 29 2015, 07:37 PM
Correct, you cannot change ROM, but you can still ...
iamalien Avatar
Posted By iamalien
Sun Mar 29 2015, 07:25 PM
i am using at89s52 i guess it is only isp not iap,...
ajay_bhargav Avatar
Posted By ajay_bhargav
Sun Mar 29 2015, 07:22 PM
Ianalien is right. But you can do this without usi...
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Posted By ajay_bhargav
Sun Mar 29 2015, 07:19 PM
EEPROM can be changed at runtime. Program memory c...
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Posted By ajay_bhargav
Sun Mar 29 2015, 07:11 PM
We have digital clock project with 4 line lcd. It ...
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Posted By ajay_bhargav
Sun Mar 29 2015, 07:07 PM
It may be possible that interrupt pin may be used ...
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Posted By ajay_bhargav
Sun Mar 29 2015, 06:58 PM
As per majoka, if you have installed the crack pro...
iamalien Avatar
Posted By iamalien
Sat Mar 28 2015, 04:48 AM
To answer it as vaguely as the question, you just ...
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Posted By iamalien
Sat Mar 28 2015, 04:27 AM
i thought that lighting led for more times should ...