LCD Display

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Definition

An LCD display can display numbers, letters and some special characters. This type of display consists of a certain number of lines, made up of a certain number of characters (eg: 2 lines of 16 characters).

Each character is made up of a matrix of dots (usually 5 x 7).

LCD displays have become essential in all applications requiring the display of parameters, so it is a Human / Machine interface.

 



Controlling an LCD display

Two display operating modes are available, 4-bit mode and 8-bit mode, modes that will be chosen when the display is initialized.

8-bit mode:



In this 8-bit mode, data is sent to the display on pins D0 to D7. We set the RS line to 0 or 1 depending on whether we want to transmit a command or data. You must also set the R / W line to 0 to indicate to the display that you want to write. It remains to send a pulse of at least 450 ns on input E, to indicate that valid data is present on pins D0 to D7. The display will read the data on the falling edge of this input.

In this 8-bit mode , the control of the LCD module requires 11 pins.

Seen from the microcontroller side, it does:

3 outputs (connected to the 3 (RS), (R / W) and (E) inputs of the LCD module)

8 pins (connected to the D7 - D0 data bus):

configured as output in write mode (R / W = 0)

configured as input in read mode (R / W = 1)

4-bit mode:


to reduce the number of wires used to control the display, such as, for example, when there are very few input/output pins available on a microcontroller. In this case, you can use the 4-bit mode of the LCD display. In this mode, only the 4 most significant bits (D4 to D7) of the display are used to transmit and read the data.

Seen from the microcontroller side, this gives:

  1. (3) outputs (connected to the 3 RS, R / W and E inputs of the LCD module)
  2. (4) pins (connected to the 4 bits of the D7 - D4 data bus):
  3. configured as output in write mode (R / W = 0)
  4. configured as input in read mode (R / W = 1)

The LCD display has 14 pins as standard and often 16, pins 15 and 16 are for backlighting (an option).


Applications:

·       LCD displays are used in:

  •        The watches
  •         Calculators
  •         Computer screens
  •        TV screens
  •     disadvantages of the LCD:

Despite all its advantages, the LCD has a few drawbacks:

  •          Dead pixels
  •          Unreadable when ambient lighting is low.
  •          Limited light (problematic in direct sunlight).
  •         The power consumption of the light source.
  •          Lamp life.



sources:

http://gilles.berthome.free.fr/02-Syntheses/E-Conversion_electriques_physiques/Synthese_afficheur_LCD.pdf

https://www.aurel32.net/elec/lcd.php.fr

http://fabrice.sincere.pagesperso-orange.fr/cm_electronique/projet_pic/LCDalpha/LCDalpha.htm

https://sciencesappliquees.com/noncato/346-cours-les-afficheurs-lcd

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