AT89S52 Mini Development Board – Serial Communication

UART (Universal Asynchronous Receiver Transmitter) is the hardware component, available in almost every microcontroller, used to transmit a byte of data serially through a single wire. To perform communication between a PC and the controller UART, the AT89S52 Development Board (Mini) has following interfaces.

RS232 interface over DB9 connector
USB interface over mini USB connector (MINI 5B)
Wireless connectivity over ZigBee

RS232.USB.Zigbee images

Additionally, communication between the controller and other peripheral modules (+5V and +3.3V) can be carried over any of the following two options.

5V connection over RMC connector
3V3 connection over RMC connector

5V.3V3 UART image

Note :

USART communication via USB/serial port is selected using jumpers J1 & J2
Short jumpers J13 & J14 while using 3V3 USART / Zigbee
Remove jumpers J1 & J2 while using Zigbee / RFID / UART (3V3/ 5V)

Schematic

The RS232 interface wields the capabilities of MAX232 while the USB interface utilizes the power of a CP2102. Desired interface for communication can be selected using the jumper connection provided on board. The code given below can be used to test the UART communication ie; up on transmitting a data the same data will be received back.

Sample Code

/**********************************************************************
                            HEADER FILE
***********************************************************************/
#include <REGX52.H>

/**********************************************************************
                        VARIABLE DECLARATIONS
***********************************************************************/
char receive=0;
char trans2[]="->Received\r\n";
int i=0;

/**********************************************************************
                           MAIN FUNCTION
***********************************************************************/
void main()
{
 TMOD = 0X21;         /* Baudrate from Timer1 in Auto-Reload mode     */
 SCON = 0X50;         /* UART Mode1 and REN set to enable Reception   */
 TF1  = 0;            /* Clear TIMER1 overflow flag                   */
 TR1  = 0;            /* Clear TR1 to turn off timer 1                */
 TH1  = 0XFD;         /* Load value to Timer 1 High Byte Register     */
 TL1  = 0XFD;         /* Load value to Timer 1 Low Byte Register      */
 TR1  = 1;            /* Set TR1 to turn on timer 1                   */
 while(1)  	
 {	 
  if(RI==1)           /* Set by hardware at the end of the 8th bit    */
  {
   RI = 0;
   receive = SBUF;    /* Store the received value in a variable       */
   SBUF    = receive; /* Transmit the received data                   */
   while(TI==0);      /* Set at the end of 8th bit transmission       */ 
   TI = 0;
   for(i=0; trans2[i]!='\0'; i++) /* Transmitting Array trans2        */
   {
    SBUF = trans2[i];
    while(TI==0);
    TI = 0;
   } 
  }
 }
}

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

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

HEADER FILE

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

#include <REGX52.H>

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

VARIABLE DECLARATIONS

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

char receive=0;

char trans2[]="->Received\r\n";

int i=0;

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

MAIN FUNCTION

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

void main()

{

TMOD = 0X21; /* Baudrate from Timer1 in Auto-Reload mode */

SCON = 0X50; /* UART Mode1 and REN set to enable Reception */

TF1 = 0; /* Clear TIMER1 overflow flag */

TR1 = 0; /* Clear TR1 to turn off timer 1 */

TH1 = 0XFD; /* Load value to Timer 1 High Byte Register */

TL1 = 0XFD; /* Load value to Timer 1 Low Byte Register */

TR1 = 1; /* Set TR1 to turn on timer 1 */

while(1)

{

if(RI==1) /* Set by hardware at the end of the 8th bit */

{

RI = 0;

receive = SBUF; /* Store the received value in a variable */

SBUF = receive; /* Transmit the received data */

while(TI==0); /* Set at the end of 8th bit transmission */

TI = 0;

for(i=0; trans2[i]!='\0'; i++) /* Transmitting Array trans2 */

{

SBUF = trans2[i];

while(TI==0);

TI = 0;

}

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

Output

Flash 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: 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