LCD Interfacing with PIC microcontroller
LCD (Liquid Crystal Display):
In recent years the Alphanumeric display(Liquid Crystal Display) has been finding widespread and replacing "Seven segment display". Why we prefer LCDs over LEDs..............
1. The declining cost of LCDs.
2. The LCD's can display numbers, characters, and graphics. In contrast,
LEDs, which are confined to display numbers and a few characters.
3.Manfacturers provide built in controller with LCD to control refresh rate as a result no need to write code in PIC18 for that task. Conversely, separate routine is required to refresh LEDs to carry displaying the information.
4. Simple programming for characters and graphics.
More importantly, LCD current(mA) requirement in comparison of seven segment displays is considerably low. Furthermore, Latest LCDs modules permit the coder to define custom character and graphics.
More importantly, LCD current(mA) requirement in comparison of seven segment displays is considerably low. Furthermore, Latest LCDs modules permit the coder to define custom character and graphics.
Once you find out how to interface it, it'll be the best and extremely reliable output device utilized by you.
Moreover, to debug the code LCD can be easily utilized if you don't have debugger.
Pin Configuration table for a 16X2 LCD character display:-
Pin Number
|
Symbol
|
Function
|
1
|
Vss
| Ground Terminal |
2
|
Vcc
| Positive Supply |
3
|
Vdd
| Contrast adjustment |
4
|
RS
| Register Select; 0→Instruction Register, 1→Data Register |
5
|
R/W
| Read/write Signal; 1→Read, 0→ Write |
6
|
E
| Enable; Falling edge |
7
|
DB0
| Bi-directional data bus, data transfer is performed once, thru DB0 to DB7, in the case of interface data length is 8-bits; and twice, through DB4 to DB7 in the case of interface data length is 4-bits. Upper four bits first then lower four bits. |
8
|
DB1
| |
9
|
DB2
| |
10
|
DB3
| |
11
|
DB4
| |
12
|
DB5
| |
13
|
DB6
| |
14
|
DB7
| |
15
|
LED-(K)
| Back light LED cathode terminal |
16
|
LED+(A)
| Back Light LED anode terminal |
Now that was all regarding the signals and also the hardware .Next, we discuss how one can send signals to LCD to display required information.
The information you want to display on LCD is kind of data signals and RS,E and RW categorized as control signals. To display data on LCD, First we send data then we put logic LOW on RS pin and RW pin and send high to low pulse to enable pin.
LCD needs a time of 39-43µS to display a character or if you want to execute any command like move the cursor on the right or left. In a similar manner, some operations like clearing display requires more time (1.63ms).Programmer must consider required time intervals when sending data, because if the defined time duration is not provided LCD controller may not display or execute commands.
Generally, Manufacturer provides two different kinds of RAMs within the LCD module ,Display data RAM which is responsible to hold the letters and the other one is Character Graphic RAM which permits user to define their custom or non standard characters.
Don't worry the above all operation can be automatically handle by using predefined library in miKroC and CSS.
Commands:
| Instruction |
Instruction Code
| Instruction Code Description | Execution time | |||||||||
RS
|
R/W
|
DB7
|
DB6
|
DB5
|
DB4
|
DB3
|
DB2
|
DB1
|
DB0
| |||
| Read Data From RAM |
1
|
1
|
D7
|
D6
|
D5
|
D4
|
D3
|
D2
|
D1
|
D0
| Read data from internal RAM |
1.53-1.64ms
|
| Write data to RAM |
1
|
0
|
D7
|
D6
|
D5
|
D4
|
D3
|
D2
|
D1
|
D0
| Write data into internal RAM (DDRAM/CGRAM) |
1.53-1.64ms
|
| Busy flag & Address |
0
|
1
|
BF
|
AC6
|
AC5
|
AC4
|
AC3
|
AC2
|
AC1
|
AC0
| Busy flag (BF: 1→ LCD Busy) and contents of address counter in bits AC6-AC0. |
39 µs
|
| Set DDRAM Address |
0
|
0
|
1
|
AC6
|
AC5
|
AC4
|
AC3
|
AC2
|
AC1
|
AC0
| Set DDRAM address in address counter. |
39 µs
|
| Set CGRAM Address |
0
|
0
|
0
|
1
|
AC5
|
AC4
|
AC3
|
AC2
|
AC1
|
AC0
| Set CGRAM Address in address counter. |
39 µs
|
| Function Set |
0
|
0
|
0
|
0
|
1
|
DL
|
N
|
F
|
X
|
X
| Set interface data length (DL: 4bit/8bit), Numbers of display line (N: 1-line/2-line) display font type (F:0→ 5×8 dots, F:1→ 5×11 dots) |
39 µs
|
| Cursor or Display Shift |
0
|
0
|
0
|
0
|
0
|
1
|
S/C
|
R/L
|
X
|
X
| Set cursor moving and display shift control bit, and the direction without changing DDRAM data |
39 µs
|
| Display & Cursor On/Off |
0
|
0
|
0
|
0
|
0
|
0
|
1
|
D
|
C
|
B
| Set Display(D),Cursor(C) and cursor blink(b) on/off control |
39 µs
|
| Entry Mode Set |
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
I/D
|
SH
| Assign cursor moving direction and enable shift entire display. |
0µs
|
| Return Home |
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
|
X
| Set DDRAM Address to “00H” from AC and return cursor to its original position if shifted. |
43µs
|
| Clear Display |
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
1
| Write “20H” to DDRAM and set DDRAM Address to “00H” from AC -Address Counter | |
Proteus Simulation of Interfacing 16X2 LCD With PIC18F4580 Microcontroller
miKroC Code for Interfacing 16X2 LCD With PIC 18F4580 Microcontroller
// LCD module connections
sbit LCD_RS at RB4_bit;
sbit LCD_EN at RB5_bit;
sbit LCD_D4 at RB0_bit;
sbit LCD_D5 at RB1_bit;
sbit LCD_D6 at RB2_bit;
sbit LCD_D7 at RB3_bit;
sbit LCD_RS_Direction at TRISB4_bit;
sbit LCD_EN_Direction at TRISB5_bit;
sbit LCD_D4_Direction at TRISB0_bit;
sbit LCD_D5_Direction at TRISB1_bit;
sbit LCD_D6_Direction at TRISB2_bit;
sbit LCD_D7_Direction at TRISB3_bit;
// End LCD module connections
char txt1[] = "Welcome";
char txt2[] = "Lcd Example";
char txt3[] = "PIC18F4580";
char txt4[] = "Hello!";
char i;
// Loop variable
void Move_Delay() {
// Function used for text moving
Delay_ms(500); // You can change the
moving speed here
}
void main(){
ADCON1 = 0xff;
CMCON = 0x7;
Lcd_Init(); // Initialize LCDa
Lcd_Cmd(_LCD_CLEAR); // Clear display
Lcd_Cmd(_LCD_CURSOR_OFF); // Cursor off
Lcd_Out(1,6,txt4); // Write text in first row
Lcd_Out(2,6,txt1); // Write text in second row
Delay_ms(2000);
Lcd_Cmd(_LCD_CLEAR); // Clear display
Lcd_Out(1,1,txt3); // Write text in first row
Lcd_Out(2,5,txt2); // Write text in second row
Delay_ms(2000);
//Moving text
for(i=0; i<4; i++) { // Move text to the right 4
times
Lcd_Cmd(_LCD_SHIFT_RIGHT);
Move_Delay();
}
while(1) { // Endless loop
for(i=0; i<8; i++) { // Move text to the left 7 times
Lcd_Cmd(_LCD_SHIFT_LEFT);
Move_Delay();
}
for(i=0; i<8; i++) { // Move text to the right 7 times
Lcd_Cmd(_LCD_SHIFT_RIGHT);
Move_Delay();
}
}
}
Proteus Simulation of Interfacing 16X2 LCD With PIC18F4580 using CSS Code
CSS Code for Interfacing 16X2 LCD With PIC 18F4580 Microcontroller
#define LCD_TYPE 2
#include <flex_lcd.c>
void main()
{
setup_adc_ports(NO_ANALOGS|VSS_VDD);
setup_adc(ADC_OFF|ADC_TAD_MUL_0);
setup_psp(PSP_DISABLED);
setup_spi(SPI_SS_DISABLED);
setup_wdt(WDT_OFF);
setup_timer_0(RTCC_INTERNAL);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
lcd_init(); // Always call this
first.
lcd_putc("\fHello World\n");
lcd_putc("");
while(1){
lcd_putc("\fHello World\n");
lcd_putc("CSS CODE Test");
delay_ms (1);
}
}
Friends for further learning about PIC18 checkout
https://microcontrollerpicavr.blogspot.com/2017/08/counter-programming-of-pic18f-using.html
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