ARM LPC2138/48 Mini Development Board – UART1 Interfacing

In ARM LPC2138/48 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

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

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

/*************************************************************************
* Function    : UART_Init                                                *
*                                                                        *
* Description : Function to initialize UART1                             *
*                                                                        *
* 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;         /* Load the character to Transmit Holding register*/
                       /* Wait here till the character is transmitted    */
 while((U1LSR & 0X20)!= 0X20);         
}

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

/*************************************************************************
* Function    : PORT_Initial                                             *
*                                                                        *
* Description : Function to initialize ports                             *
*                                                                        *
* Parameters  : None                                                     *
**************************************************************************/ 
void PORT_Initial(void)    
{
 PINSEL0 = 0x00050000;              /* TXD & RXD for P0.8 & P0.9 resp.   */          
}

/*************************************************************************
                              MAIN FUNCTION
**************************************************************************/
int main()
{
 PORT_Initial();                    /* Initialize the ports              */
 UART_Init();                       /* Initialize UART1                  */
 UART_String("Checking UART1");
 while(1)
 {
  if((U1LSR&0X01)==0X01)            /* RDR set when U1RBR contains data  */
  {
   U1THR = U1RBR;                   /* Transmit the received character   */
   while((U1LSR&0X20)!=0X20);
  }
 }
}

/**************************  END OF PROGRAM  *****************************/

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

HEADER FILE

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

#include<lpc21xx.h>

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

* Function : UART_Init *

* *

* Description : Function to initialize UART1 *

* *

* 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; /* Load the character to Transmit Holding register*/

/* Wait here till the character is transmitted */

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

}

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

* Function : UART_String *

* *

* Description : Function to transmit string *

* *

* Parameters : String to be transmitted *

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

void UART_String(unsigned char *dat)

{

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

{

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

dat++; /* Increment the pointer */

}

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

* Function : PORT_Initial *

* *

* Description : Function to initialize ports *

* *

* Parameters : None *

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

void PORT_Initial(void)

{

PINSEL0 = 0x00050000; /* TXD & RXD for P0.8 & P0.9 resp. */

}

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

MAIN FUNCTION

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

int main()

{

PORT_Initial(); /* Initialize the ports */

UART_Init(); /* Initialize UART1 */

UART_String("Checking UART1");

while(1)

{

if((U1LSR&0X01)==0X01) /* RDR set when U1RBR contains data */

{

U1THR = U1RBR; /* Transmit the received character */

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

}

/************************** END OF PROGRAM *****************************/

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 correct port

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

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- LPC 2148
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