matlab interface with pic16f877a

Hi there,

I want to make a simple program to tell my PIC which LED to turn on when I send an 'integer' data from my Matlab. Here's my matlab code. anything wrong with it?

    serialport = serial('COM3');
    set(serialport,'BaudRate',19200);
    fopen(serialport);
    fprintf (serialport,'1');
    fclose(serialport);

and my PIC code is

#include <htc.h>
#include <pic.h>

__CONFIG(0x3F32);

#define LED1    RB6    //red LED1
#define LED2    RB7    //red LED2

unsigned int UART_read(void);
void UART_write(unsigned char data);

unsigned int rc_text,x;
unsigned int t_data;

//  main function
//================================================================
void main(void)
{
  
  
  TRISC6=0;  
  TRISC7=1;  
  TX9=0;    
  TXEN=1;    
  SYNC=0;    
  BRGH=1;    
  SPEN=1;    
  RX9=0;    
  CREN=1;    
  SPBRG=64;  
  TXIE=0;    
  RCIE=0;    

  TRISB=0b00000000;
while(1)
{
  RCREG=0;  //clear receive buffer

  x=UART_read();
  

  if (rc_text==1)
{

  RB6 = 1;
}
else if (rc_text==2)
  RB7 = 1;
else if (rc_text==3)
  RB3 = 1;

  if (RB4==1);
  t_data = 999;

  UART_write(t_data);

}  
}

unsigned int UART_read(void)
{
  while(RCIF==1)

  rc_text = RCREG;

}

//function to write a byte out to UART TX
void UART_write(unsigned char data)
{
  while(TXIF==0);  //wait for the previous UART transmission to complete
  TXREG=data;      //write data for transmission
}

somebody please help!

Answer 1

[Walter Roberson]

Your UART_read() code has no return statement in it. What value is it returning? What if RCIF starts out 0, then why is rc_text being left unchanged?

Your main() routine is looking for integer value 1, but your MATLAB code is writing the character '1' (integer value 49). Change your line

fprintf (serialport,'1');

to

fwrite(serialport, uint8(1));

[Shi Wei Foo]

Thanks Walter for reply.

the return statement is wrong. I've changed my code to this. Is this code correct?

while(1)

{

RCREG=0; //clear receive buffer

while(RCIF == 0);

x=UART_read();

if (x==1)

{

RB6 = 1;

}

else if (x==2)

RB7 = 1;

else if (x==3)

RB3 = 1;

if (RB4==1);

t_data = 999;

UART_write(t_data);

}

}

Thanks.

[Walter Roberson]

I do not know enough about the device to know if the revised code is correct.

You should not have the semi-colon after if (RB4==1) unless you want to do nothing in that case.

If you are trying to set t_data to 999 only in the case that RB4==1 then you have the problem that you are not setting t_data in any other condition.

Writing 999 to the UART is going to be a problem unless the MATLAB end is expecting to receive a 16 bit value and writing to the UART transmits a 16 bit value. If the UART only transmits 8 bits (which would be consistent with the rest of what you are doing), then the value transmitted would be 231, which is 999 mod 256.