A1.8051 Interfacing:LCD 16x2
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Introduction:LCD

Liquid Crystal Display(LCDs) provide a cost effective way to put a text output unit for a microcontroller. As we have seen in the previous tutorial, LEDs or 7 Segments do no have the flexibility to display informative messages. This display has 2 lines and can display 16 characters on each line. Nonetheless, when it is interfaced with the micrcontroller, we can scroll the messages with software to display information which is more than 16 characters in length.

LCD Internal Controller

Fig 1: LCD Block diagram


The LCD is a simple device to use but the internal details are complex. Most of the 16x2 LCDs use a Hitachi HD44780 or a compatible controller. Yes, a micrcontroller is present inside a Liquid crystal display as shown in figure 1.

The Display Controller takes commands and data from a external microcontroller and drivers the LCD panel(LCDP). It takes a ASCII value as input and generate a patter for the dot matrix. E.g., to display letter 'A', it takes its value 0X41(hex) or 65(dec) decodes it into a dot matrix of 5x8 as shown in figure 2.

Basic Commands

The LCD controller uses RS and RW lines along with E to operate the LCD.

  • Resister Select (RS): Determines weather a command(RS = 0) is sent (to set up the display) or actual data(RS=1) is sent.
  • Read/Write RW=0; writes to the LCD. RW=1;Reads from the LCD.

The commonly used instructions are shown in the instruction set below. Observe the Bit names: I/D, S, D, C etc at the bottom of instruction set to decode the instructions completely.

  • Clear Display
  • Cursor Home
  • Set Entry Mode
  • Display on/off control
  • Cursor/display shift
  • Function Set
  • Read Busy Flag
  • Data Read
  • Data Write

Instruction Set

HD44780U based instruction set
Instruction Code Description
RS R/W B7 B6 B5 B4 B3 B2 B1 B0
Clear display 0 0 0 0 0 0 0 0 0 1 Clears display and returns cursor to the home position (address 0).
Cursor home 0 0 0 0 0 0 0 0 1 * Returns cursor to home position. Also returns display being shifted to the original position. DDRAM content remains unchanged.


Entry mode set 0 0 0 0 0 0 0 1 I/D S Sets cursor move direction (I/D); specifies to shift the display (S). These operations are performed during data read/write.


Display on/off control 0 0 0 0 0 0 1 D C B Sets on/off of all display (D), cursor on/off (C), and blink of cursor position character (B).


Cursor/display shift 0 0 0 0 0 1 S/C R/L * * Sets cursor-move or display-shift (S/C), shift direction (R/L). DDRAM content remains unchanged.


Function set 0 0 0 0 1 DL N F * * Sets interface data length (DL), number of display line (N), and character font (F).
Read busy flag &
address counter 		0 1 BF CGRAM/DDRAM address Reads busy flag (BF) indicating internal operation being performed and reads CGRAM or DDRAM address counter contents (depending on previous instruction).
Write CGRAM or
DDRAM 		1 0 Write Data Write data to CGRAM or DDRAM.
Write CGRAM or
DDRAM 		1 0 Write Data Write data to CGRAM or DDRAM.
Instruction bit names —

I/D - 0 = decrement cursor position, 1 = increment cursor position;

S - 0 = no display shift, 1 = display shift;
D - 0 = display off, 1 = display on;
C - 0 = cursor off, 1 = cursor on;
B - 0 = cursor blink off, 1 = cursor blink on ;
S/C - 0 = move cursor, 1 = shift display;
R/L - 0 = shift left, 1 = shift right;
DL - 0 = 4-bit interface, 1 = 8-bit interface;
N - 0 = 1/8 or 1/11 duty (1 line), 1 = 1/16 duty (2 lines);
F - 0 = 5×8 dots, 1 = 5×10 dots;
BF - 0 = can accept instruction, 1 = internal operation in progress.

LCD UNIT

Fig2: LCD_turn_on

It is also possible to generate dot matrix patterns for custom characters and special symbols.

Let us look at a pin diagram of a commercially available LCD like JHD162 which uses a HD44780 controller and then describe its operation.

PIN NUMBER FUNCTION
1 Ground
2 VCC
3 Contrast adjustment (VO)
4 Register Select (RS). RS=0: Command, RS=1: Data
5 Read/Write (R/W). R/W=0: Write, R/W=1: Read
6 Clock (Enable). Falling edge triggered
7 Bit 0 (Not used in 4-bit operation)
8 Bit 1 (Not used in 4-bit operation)
9 Bit 2 (Not used in 4-bit operation)
10 Bit 3 (Not used in 4-bit operation)
11 Bit 4
12 Bit 5
13 Bit 6
14 Bit 7
15 Back-light Anode(+)
16 Back-Light Cathode(-)
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