ARM LPC2129 Mini Development Board – UART1 Interfacing

In ARM LPC2129 Mini Development Board, UART1 is accessible through connector K12 that has 3 pins namely GND,TXD1 & RXD1.

TXD1 – Transmission pin of UART1 (P0.8)
RXD1 – Reception pin of UART1 (P0.9)
GND – Common ground

Schematic:

Sample code to test both transmission & reception of UART1 module is given below. The code initially transmits the string “Checking UART1” and on receiving a character, the same gets retransmitted.

Sample Code

/**************************************************************************************
                                   HEADER FILES
***************************************************************************************/
#include<lpc21xx.h>

/**************************************************************************************
* Function    : UART_Init                                                             *
*                                                                                     *
* Description : Function for USART Initialisation                                     *
*                                                                                     *
* Parameters  : None                                                                  *
***************************************************************************************/
void UART_Init(void)
{
 U1LCR = 0X83;                         /* DLAB=1, 8 bit character                     */				
 U1DLL = 0XC3;                         /* Divisor Latch LSB                           */				
 U1DLM = 0X00;                         /* Divisor Latch MSB                           */			
 U1LCR = 0X03;                         /* DLAB=0, 8 bit character                     */				
}

/**************************************************************************************
* Function    : UART_Data                                                             *
*                                                                                     *
* Description : Function to transmit single character                                 *
*                                                                                     *
* Parameters  : data - character to be transmitted                                    *
***************************************************************************************/ 
void UART_Data(unsigned char data)
{
 U1THR = data;                         /* Data for transmission                       */
 while((U1LSR & 0X20)!= 0X20);         /* Wait here till the character is transmitted */
}

/**************************************************************************************
* Function    : UART_String                                                           *
*                                                                                     *
* Description : Function to transmit string                                           *
*                                                                                     *
* Parameters  : String to be transmitted                                              *
***************************************************************************************/
void UART_String(unsigned char *dat)
{
 while(*dat!='\0')                     /* Checking for termination character          */
 {
  UART_Data(*dat);                     /* Transmit the character                      */
  dat++;                               /* Increment the pointer                       */
 } 
}

/**************************************************************************************
* Function    : PORT_Initial                                                          *
*                                                                                     *
* Description : Function for PORT Initialisation                                      *
*                                                                                     *
* Parameters  : None                                                                  *
***************************************************************************************/
void PORT_Initial(void)    
{
 PINSEL0     =    0x00050000;          /* RXD & TXD selected                          */          
} 

/**************************************************************************************
                                   MAIN FUNCTION
***************************************************************************************/	
int main()
{
 PORT_Initial();                       /* Initialise the ports                        */
 UART_Init();                          /* Initialise UART                             */
 UART_String("Checking UART1");
 while(1)
 {
  if((U1LSR&0X01)==0X01)
  {
    U1THR  = U1RBR;
    while((U1LSR&0X20)!=0X20);
  }
 }
}
/**************************************END*********************************************/

/**************************************************************************************

HEADER FILES

***************************************************************************************/

#include<lpc21xx.h>

/**************************************************************************************

* Function : UART_Init *

* *

* Description : Function for USART Initialisation *

* *

* Parameters : None *

***************************************************************************************/

void UART_Init(void)

{

U1LCR = 0X83; /* DLAB=1, 8 bit character */

U1DLL = 0XC3; /* Divisor Latch LSB */

U1DLM = 0X00; /* Divisor Latch MSB */

U1LCR = 0X03; /* DLAB=0, 8 bit character */

}

/**************************************************************************************

* Function : UART_Data *

* *

* Description : Function to transmit single character *

* *

* Parameters : data - character to be transmitted *

***************************************************************************************/

void UART_Data(unsigned char data)

{

U1THR = data; /* Data for transmission */

while((U1LSR & 0X20)!= 0X20); /* Wait here till the character is transmitted */

}

/**************************************************************************************

* Function : UART_String *

* *

* Description : Function to transmit string *

* *

* Parameters : String to be transmitted *

***************************************************************************************/

void UART_String(unsigned char *dat)

{

while(*dat!='\0') /* Checking for termination character */

{

UART_Data(*dat); /* Transmit the character */

dat++; /* Increment the pointer */

}

/**************************************************************************************

* Function : PORT_Initial *

* *

* Description : Function for PORT Initialisation *

* *

* Parameters : None *

***************************************************************************************/

void PORT_Initial(void)

{

PINSEL0 = 0x00050000; /* RXD & TXD selected */

}

/**************************************************************************************

MAIN FUNCTION

***************************************************************************************/

int main()

{

PORT_Initial(); /* Initialise the ports */

UART_Init(); /* Initialise UART */

UART_String("Checking UART1");

while(1)

{

if((U1LSR&0X01)==0X01)

{

U1THR = U1RBR;

while((U1LSR&0X20)!=0X20);

}

/**************************************END*********************************************/

OUTPUTFlash the code into the controller and connect it to PC using suitable interface.. Various steps to check the output using RealTerm are given below.

Step 1: Launch RealTerm

Step 2: RealTerm opens as shown below

Step 3: Go to ‘Port’ option, set correct baudrate (which is set as 9600 in the sample code) and give correct port number.

Step 4: Click ‘Change’ (encircled in red) to apply the changes. Now check the status of Port. If it is closed, click ‘Open’ button (encircled in green) to open it.

Step 5: The data transmitted from the board can be viewed as shown below.

Step 6: To check reception, go to Send option, type the string in the space provided(encircled in green) and click Send ASCII button. The first “hello” in green colour is transmitted from PC & that in yellow colour is retransmitted by the controller