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Sample C program: LCD interface to ARM Cortex M0 MCU

LCD interface to STM32F0 discovery embedded board


In most of the embedded systems applications, the need for a display is must. If any text /numeric data and graphics/image need to be displayed, use of LCD display panel is a must. The basics of LCD display is already explained in the module17. In this module we will explain both hardware connection (wiring) and sample program/code in C language to display alphanumeric text on a simple LCD display panel.

The LCD display panel we have selected is STN type LCD panel with 16 characters in 2 rows (16x2). The specifications and the datasheet for LCD display called JHD162A is available at http://www.hantronix.com/files/data/1278554733char-comm.pdf and http://www.itron.com.cn/PDF_file/JHD162A%20SERIES.pdf. 16x2 JHD162A LCD display panel is easily available in most of the electronics component shops in India and other places in the world. You should buy the LCD panel fitted on a PCB as shown in the picture below:

lcd panel

Hardware Interface:

Components/parts required:

1. 32 bit MCU based STM32F0 discovery embedded board
2. LCD Panel: JHD 162A
3. Trim pot 10 Kilo ohms
4. 220 Ohms resistor
5. General purpose PCB.
6. External +5V power supply


LCD pin details:

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Summary on LCD Panel: JHD162A LCD module powers up in 8-bit mode. Additional commands are required to put the module into 4-bit mode. In this example, we are using LCD panel in 8-bit mode. 16x2 means there are 16 columns and 2 rows of alphanumeric ASCII blocks on the LCD.

control signals:

R/W: When this signal is '1' = Reads data from the LCD RAM. When this signal is '0' = Writes data on LCD RAM.
EN: Is basically a Latch signal. You have to send '1' first and then '0' signal with a particular delay to latch the data.
RS: Is a Register Select Control signal. When this signal is '1' = It accepts data to be displayed. When this signal is '0' = It accepts instructions for the LCD like setting font, cursor position etc.


Databus (D0 to D7): Is 8-bit Databus. It is used to send both data as well as Instructions to the LCD based upon control signals.

Backlight + and Backlight GND: Turns on Backlight of that LCD so that you can see the words correctly.
VEE: is a contrast voltage. Using a trim pot you can adjust the contrast of the LCD. More voltage more the contrast and vice versa(voltage should never exceed VCC = +5 volts).

Circuit diagram(below): Connect STM32F0-DISCOVERY embedded board to the LCD panel.

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LCD Initialization

1. Initializations for LCD Communications: First set RS= 0, R/W=0, EN=1; And give 10ms delay, then write the hex code (0X0001 & latch, 0X0038 & latch , 0X000E & latch,0X0010 & latch, 0X0006 & latch) on data bus(PA0-PA7). The C code below has all this taken care.

Table below: Code of various display commands

Command Code
Clear Display, Cursor to Home 0x0001
Cursor to Home 0x0002
Entry Mode:  
Cursor Decrement, Shift off 0x0004
Cursor Decrement, Shift on 0x0005
Cursor Increment, Shift off 0x0006
Cursor Increment, Shift on 0x0007
Display Control:  
Display, Cursor, and Cursor Blink off 0x0008
Display on, Cursor and Cursor Blink off 0x000C
Display and Cursor on, Cursor Blink off 0x000E
Display, Cursor, and Cursor Blink on 0x000F
Cursor / Display Shift: (nondestructive move)  
Cursor shift left 0x0010
Cursor shift right 0x0014
Display shift left 0x0018
Display shift right 0x001C
Display Function (2 rows for 4-bit data; big) 0x002C
Display Function (2 rows for 4-bit data; small)) 0x0028
Display Function (1 row for 4-bit data; big) 0x0024
Display Function (1 row for 4-bit data; small) 0x0020
Display Function (2 rows for 8-bit data; big) 0x003C
Display Function (2 rows for 8-bit data; small) 0x0038
Display Function (1 row for 8-bit data; big) 0x0034
Display Function (1 row for 8-bit data; small) 0x0030
Move cursor to beginning of second row 0x00C0


2.Ready to Write Data to LCD Data
You have to Change RS=1 after executing above instructions.

Table below: Codes for displaying different ASCII and other characters on LCD panel

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Example: To display character 'P' is 0101 0000 = 0x0050 on this LCD Character RAM.

 

Below is the code written to display character 'www.eeherald.com' on JHD 162A.


#include "main.h"
#include "stm32f0xx_conf.h"
uint32_t TickValue=0;

#define RS GPIO_Pin_13 // RS is named as Port 13
#define RW GPIO_Pin_14 // RW is named as Port 14
#define EN GPIO_Pin_15 // EN is named as Port 15

//------------------------------------------------------------------------------
// Function Name : delay_ms
// Description : delay for some time in ms unit(accurate)
// Input : n_ms is how many ms of time to delay
//------------------------------------------------------------------------------
void TimingDelay_Decrement(void)
{
TickValue--;
}

void delay_ms(uint32_t n_ms)
{
SysTick_Config(8000*PLL_MUL_X - 30);
TickValue = n_ms;
while(TickValue == n_ms)
;
SysTick_Config(8000*PLL_MUL_X);
while(TickValue != 0)
;
}
//------------------------------------------------------------------------------
// Function Name : Init GPIO
// Description : pins ,port clock & mode initialization.
//------------------------------------------------------------------------------
void initgpio()
{
GPIO_InitTypeDef GPIO_InitStructure;
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA | RCC_AHBPeriph_GPIOC, ENABLE);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15 ;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOC, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0 | GPIO_Pin_1 | GPIO_Pin_2 | GPIO_Pin_3 | GPIO_Pin_4 | GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_10MHz;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_Init(GPIOA, &GPIO_InitStructure);


}
//------------------------------------------------------------------------------
// Function Name : s_init
// Description : Send Instruction Function (RS=0 & RW=0)
//------------------------------------------------------------------------------

void s_init()
{
GPIOC->BRR=RS;
GPIOC->BRR=RW;
}
//------------------------------------------------------------------------------
// Function Name : s_data
// Description : Send Data Select routine(RS=1 & RW=0)
//------------------------------------------------------------------------------

void s_data()
{
GPIOC->BSRR=RS;
GPIOC->BRR=RW;
}
//------------------------------------------------------------------------------
// Function Name : s_latch
// Description : Latch Data/Instruction on LCD Databus.
//------------------------------------------------------------------------------

void s_latch()
{
GPIOC->BSRR=EN;
delay_ms(10);
GPIOC->BRR=EN;
delay_ms(10);
}

/*******************************************************************************
* Function Name : main
* Description : Main program.
*******************************************************************************/
int main(void) //Main function
{

initgpio();

int k=0;
char a[]="WWW.EEHERALD.COM";
char b[]="EMBEDDED SYSTEMS";

GPIOC->BRR=RS; //Initialize RS=0 for selecting instruction Send
GPIOC->BRR=RW; // Select RW=0 to write Instruction/data on LCD
GPIOC->BSRR=EN; // EN=1 for unlatch. (used at initial condition)

delay_ms(10);

s_init(); //Call Instruction Select routine
GPIOA->ODR=0x0001; // Clear Display, Cursor to Home
s_latch(); //Latch the above instruction
GPIOA->ODR=0x0038; // Display Function (2 rows for 8-bit data; small)
s_latch(); //Latch this above instruction 4 times
s_latch();
s_latch();
s_latch();
GPIOA->ODR=0x000E; // Display and Cursor on, Cursor Blink off
s_latch(); //Latch the above instruction
GPIOA->ODR=0x0010; // Cursor shift left
s_latch(); //Latch the above instruction
GPIOA->ODR=0x0006; // Cursor Increment, Shift off
s_data(); //Change the input type to Data.(before it was instruction input)
s_latch(); //Latch the above instruction

for(k=0;a[k];k++)
{
GPIOA->ODR=a[k]; //It will send a[0]='P' as = '0x0050' on Port A.
s_latch(); //Latch the above instruction only once. Or it will clone each character twice if you latch twice.
}
GPIOC->BRR=RS; //Initialize RS=0 for selecting instruction Send
GPIOC->BRR=RW; // Select RW=0 to write Instruction/data on LCD
GPIOC->BSRR=EN; // EN=1 for unlatch. (used at initial condition)

delay_ms(10);
GPIOA->ODR=0x00C0; // Move cursor to beginning of second row
s_latch(); //Latch the above instruction
s_data(); //Change the input type to Data.(before it was instruction input)
for(k=0;b[k];k++)
{
GPIOA->ODR=b[k]; //It will send b[0]='E' as = '0x0044' on Port A.
s_latch();//Latch the above instruction only once. Or it will clone each character twice if you latch twice.
}
s_init();
}

 

This module is part of complete embedded systems course available at www.eeherald.com. The other modules of the course based on diffrent kits used are listed in the table below.

Stream-Discovery Stream-LPCXpresso Stream-AME-51

Module 3b: Installation of ARM Cortex M0 based STM32F0 kit from ST Microelectronics and sample code

Module 4: Sample programs -1 for ARM Cortex M0 based on STM32F0

Module 5b: ARM Cortex M0 Architecture.

Module 6b: Sample program-2 (interfacing keypad)

Module 7: Serial communication concepts -1

Module 8: RS-232 Basics

Module 9: Controller Area Networking (CAN)

Module 10: LIN

Module 11: I2C Bus Interface

Module 12: SPI Bus Interface

Module14: USB Interface

Module15: SRAM memory interface

Module16: Flash memory interface

Module17: LCD display panel interface

Module18: Touch pane interface

Module19: Audio/video interface

Module 3a: Installation of ARM Cortex M0 based LPCXpresso kit from NXP Semiconductor and sample code

Module 4: Sample programs -1 for ARM Cortex M0 based LPCXpress

Module 5a: ARM Cortex M0 Architecture.

Module 6a: Sample program-2 (interfacing keypad)

Module 7: Serial communication concepts -1

Module 8: RS-232 Basics

Module 9: Controller Area Networking (CAN)

Module 10: LIN

Module 11: I2C Bus Interface

Module 12: SPI Bus Interface

Module14: USB Interface

Module15: SRAM memory interface

Module16: Flash memory interface

Module17: LCD display panel interface

Module18: Touch pane interface

Module19: Audio/video interface

Module 3: Installation of OKI's ARM7 KIT(old module, suggest to skip this module)

Module 4: Sample programs -1 for ARM7 TDMI MCU

Module 5: OKI ARM-7 Processor Architecture.

Module 6: Sample programs -2 for ARM7 TDMI MCU

Module 7: Serial communication concepts -1

Module 8: RS-232 Basics

Module 9: Controller Area Networking (CAN)

Module 10: LIN

Module 11: I2C Bus Interface

Module 12: SPI Bus Interface

Module14: USB Interface

Module15: SRAM memory interface

Module16: Flash memory interface

Module17: LCD display panel interface

Module18: Touch pane interface

Module19: Audio/video interface

 

 

 


 

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