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LCD's
1
LCD Types
Many types available. Most
common are:
Character
Pre-programmed with a set of
alphanumeric characters & symbols
Size range from 8×1 to 40×4 (characters)
Graphic
Either graphic only (set each pixel
individually ), or both graphic & character
modes
Common sizes (pixels) 128×64, 240×128,
320×240 (QVGA) etc..
4-2
LCD backlights & Display properties
Backlights
CCFL (needs converter), LED & OLED (no backlight required)
Display properties
Reflective,Transmissive, Transflective (better in sunlight)
4-3
LCD polarizer
Reflective displays have an opaque rear polarizer that includes a diffuse reflector, such
as brushed aluminum. This layer reflects polarized ambient light that has entered the front
of the display back trough the LCD cell. Reflective displays require ambient light to be
seen. They exhibit high brightness, excellent contrast, and wide viewing angles. They are
particularly suitable for use in battery operated equipment where an adequate level of light
is always available. Reflective LCD's cannot be backlit, however they can be front lighted
in some applications.
Transmissive displays have a clear polarizer on the front and the back. The display
therefore depends on light coming through from the back of the display toward the
observer in order to be seen. Most, but not all transmissive displays are negative image,
and we sometimes add colored filters to different areas of the display to highlight
different annunciators. Another example of a transmissive polarizer display would be a
transparent window where you could see the segments superimposed over your line of
vision through the display window (this assumes a sufficient ambient light source exists
on either side of the window).
Transflective displays have a rear polarizer which includes a translucent material
which reflects part of the ambient light, and also transmits backlighting. As the name
implies, it is a compromise between the transmissive and reflective viewing mode.
Used in reflection, it is not as bright and has lower contrast than the reflective type
LCD, but it can be backlit for use in low light conditions. This polarizer is the best
selection for a display that can be used in all lighting conditions with a backlight.
Source - http://www.pacificdisplay.com/lcd_polarizers.htm 4-4
LCD Pin assignments
Pin
Symbol Level I/O Function
number
1 Vss - - Power supply (GND)
2 Vcc - - Power supply (+5V)
3 Vee - - Contrast adjust
0 = Instruction input
4 RS 0/1 I
1 = Data input
0 = Write to LCD module
5 R/W 0/1 I
1 = Read from LCD module
6 E 1, 1-->0 I Enable signal
7 DB0 0/1 I/O Data bus line 0 (LSB)
8 DB1 0/1 I/O Data bus line 1
9 DB2 0/1 I/O Data bus line 2
10 DB3 0/1 I/O Data bus line 3
11 DB4 0/1 I/O Data bus line 4
12 DB5 0/1 I/O Data bus line 5
13 DB6 0/1 I/O Data bus line 6
14 DB7 0/1 I/O Data bus line 7 (MSB)
4-5
LCD Driver Block Diagram
4-6
LCD on the MCB23XX Boards
Keil MCB23xx uses 4 bit mode!
LCD Pins LPC23XX pins
- DB4 = P1.24
- DB5 = P1.25
- DB6 = P1.26
- DB7 = P1.27
-E = P1.31 (for V1 P1.30)
- RW = P1.29
- RS = P1.28
4-7
Commands for character modules
RS R/W DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
Function
set 0 0 0 0 1 DL N F * #
4-8
4 Bit initialization
LCD_RS(0) /* Instruction input*/
lcd_write_4bit (0x3); /* Set LCD in known state */
delay (4100); /* Write 0x3 × 3 */
lcd_write_4bit (0x3);
delay (100);
lcd_write_4bit (0x3);
lcd_write_4bit (0x2); /* Select 4-bit interface */
lcd_write_cmd (0x28); /* 2 lines, 5x8 character matrix*/
lcd_write_cmd (0x0C); // Dsplayn cntrl:Disp=ON,Curs/Blk=OFF
lcd_write_cmd (0x06); /* Entry mode: Move right, no shift */
4-9
DISPLAY CHARACTER POSITION AND
CHARACTER ADDRESS
4-10
LCD Functions
User functions - call these from your program (function prototypes are in
the lcd header file!)
void lcd_init (void);
void lcd_clear (void);
void lcd_putchar (char c);
void set_cursor (unsigned char column, unsigned char line);
void lcd_print (unsigned char const *string);
Extract from sample program
lcd_init();
lcd_clear();
lcd_print (" Embedded Systems");
set_cursor (0, 1);
lcd_print (" Alan ");
4-11
Low level non user LCD functions
Also a number of low level functions that are called from the
user functions see the lcd.c file.
void lcd_write_cmd (unsigned char c)
void lcd_write_4bit (unsigned char c)
static unsigned char wait_while_busy (void)
static unsigned char lcd_read_status (void)
void lcd_write_cmd (unsigned char c)
{
wait_while_busy();
LCD_RS(0)
lcd_write_4bit (c>>4);
lcd_write_4bit (c);
}
4-12
Printing variables to the LCD
To print variables to the LCD it is necessary to convert the variable to its
ASCII character representation using the sprintf() function and then
printing out the characters using the lcd_print() function.
Example
sprintf(lcd_buf, "%d", x); //convert x to ASCII
lcd_print(lcd_buf); // print to LCD
where the variable x is an integer to be printed in decimal (hence the %d
in the sprintf format string) and lcd_buf is an array of char declared big
enough to hold the characters of the number + 1 extra character (for the
end of string NULL character).
E.g. char lcd_buf[17]; // LCD buffer big enough for one line of characters
on the LCD
4-13
LCD Character generation
User defines characters can be stored in the LCD CGRAM memory
Up to 8 characters can be stored
Column Bits Hex
0 1 2 3 4 7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0 0 0 0
1 1 1 0 0 0 0 1 0 1 0 0 A
2 0 0 0 0 0 0 0 0 0 0
Rows
3 0 0 0 0 0 0 0 0 0 0
4 1 1 0 0 0 1 0 0 0 1 1 1
5 1 1 1 0 0 0 0 1 1 1 0 0 E
6 0 0 0 0 0 0 0 0 0 0
7 0 0 0 0 0 0 0 0 0 0
4-14
LCD CG RAM Example
/* Load user-specific characters into CGRAM */
lcd_write_cmd(0x40); /* Set CGRAM address counter to 0 */
p = &UserFont[0][0];
for (i = 0; i < sizeof(UserFont); i++, p++)
lcd_putchar (*p);
lcd_write_cmd(0x80); /* Set DDRAM address counter to 0 */
/* 8 user defined characters to be loaded into CGRAM (used for
bargraph) */
const unsigned char UserFont[8][8] = {
{ 0x00,0x0A,0x00,0x00,0x11,0x0e,0x00,0x00 },
{ 0x10,0x10,0x10,0x10,0x10,0x10,0x10,0x10 },
{ 0x18,0x18,0x18,0x18,0x18,0x18,0x18,0x18 },
{ 0x1C,0x1C,0x1C,0x1C,0x1C,0x1C,0x1C,0x1C },
{ 0x1E,0x1E,0x1E,0x1E,0x1E,0x1E,0x1E,0x1E },
{ 0x1F,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F },
{ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 },
{ 0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00 }
};
4-15
LCD CG RAM Example
Our character has been defined at address 0x00;
Therefore to display the user defined character
simply use the lcd_putchar function.
lcd_putchar (0x00);
4-16
LCD simulation in uVision
Add the file Sim.ini to the directory of your current
project.
In the Options for target simulator (magic wand icon)
select the debug tab.
4-17
LCD simulation in uVision
Add the file Sim.ini as the Initialization file in the left hand
panel for the simulator options using the file browser icon.
4-18
LCD simulation in uVision
The Sim.ini maps the LCD write
address to 0x1000000 in
memory.
By viewing address 0x10000000
in the memory window it is
possible to simulate the display
of the LCD.
4-19
LCD simulation in uVision
Change display format to Ascii
4-20
