ARM LPC2138/48 Mini Development Board – UART0 Interfacing

LPC2138/48 has two UART modules namely UART0 and UART1. It has only asynchronous (no clock connection) mode of operation. For UART0 communication transmission & reception pins are respectively P0.0 & P0.1.
In the mini development board, UART0 can communicate through

USB port via CP2102
Serial port via MAX232
RMC connector K14(GND,TXD0,RXD0,Vout) in 3.3V/5V levels
Zigbee

Schematic

Note:

UART0 communication via USB/serial port is selected using jumpers J7 & J9
While using UART0 for communication, PROGRAMMER switch should be in manual mode.
Through RMC connector, UART0 can be used in two voltage levels of 3V3/5V which can be selected by jumper J16
While using Zigbee, remove jumpers J7 & J9

Sample Code

Sample code to test both transmission & reception of UART0 is given below. Initially the string “Checking UART0” gets transmitted and on receiving a character, it gets retransmitted.

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

/*************************************************************************
* Function    : UART_Init                                                *
*                                                                        *
* Description : Function to initialize UART0                             *
*                                                                        *
* Parameters  : None                                                     *
**************************************************************************/
void Uart_Init(void)
{
 U0LCR = 0X83;        /* 8 bit character length, DLAB access enabled     */
 U0DLL = 0XC3;        /* The UART0 Divisor Latch LSB Register, and       */
 U0DLM = 0X00;        /* U0DLM loaded with value for 9600 baudrate       */
 U0LCR = 0X03;        /* DLAB access disabled                            */
} 

/*************************************************************************
* Function    : UART_Data                                                *
*                                                                        *
* Description : Function to transmit single character                    *
*                                                                        *
* Parameters  : data - character to be transmitted                       *
**************************************************************************/
void Uart_Data(unsigned char data)
{
 U0THR = data;        /* Load the character to Transmit Holding register */ 
                      /* THRE set when transmission complete             */
 while((U0LSR & 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 = 0x00000005;      /* Functions TXD & RXD for P0.0 & P0.1 resp. */
} 

/*************************************************************************
                             MAIN FUNCTION
**************************************************************************/
int main()
{
 Port_Initial();                    /* Initialize the ports              */
 Uart_Init();                       /* Initialize UART0                  */
 Uart_String("Checking UART0");     /* Transmit the string               */
 while(1)
 {
  if((U0LSR&0X01)==0X01)            /* RDR set when U0RBR contains data  */
  {
   U0THR = U0RBR;                   /* Transmit the received character   */
   while((U0LSR&0X20)!=0X20);
  }
 }
}

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

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

HEADER FILE

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

#include<lpc21xx.h>

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

* Function : UART_Init *

* *

* Description : Function to initialize UART0 *

* *

* Parameters : None *

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

void Uart_Init(void)

{

U0LCR = 0X83; /* 8 bit character length, DLAB access enabled */

U0DLL = 0XC3; /* The UART0 Divisor Latch LSB Register, and */

U0DLM = 0X00; /* U0DLM loaded with value for 9600 baudrate */

U0LCR = 0X03; /* DLAB access disabled */

}

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

* Function : UART_Data *

* *

* Description : Function to transmit single character *

* *

* Parameters : data - character to be transmitted *

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

void Uart_Data(unsigned char data)

{

U0THR = data; /* Load the character to Transmit Holding register */

/* THRE set when transmission complete */

while((U0LSR & 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 = 0x00000005; /* Functions TXD & RXD for P0.0 & P0.1 resp. */

}

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

MAIN FUNCTION

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

int main()

{

Port_Initial(); /* Initialize the ports */

Uart_Init(); /* Initialize UART0 */

Uart_String("Checking UART0"); /* Transmit the string */

while(1)

{

if((U0LSR&0X01)==0X01) /* RDR set when U0RBR contains data */

{

U0THR = U0RBR; /* Transmit the received character */

while((U0LSR&0X20)!=0X20);

}

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

OutputThe following screenshots explain how to test the sample code using RealTerm (click to download).

Step 1: Open 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

Topics related to ARM LPC2138/48 Mini Development Board

Resources

Softwares
- Keil uVision4 IDE
- Flash Utility Tool
Datasheets
- LPC 2148
- LPC 2138
- MCP 9700
- LM 7805
- LD 1117
- MAX 232

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