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PIC18F and USART

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adrianvon

Member
Hi,

I am using USART with the PIC18F4550 and Visual Studio. Can someone help me find what is causing errors in the coding below please?

Code:
void main(void)
{
  Configurate_USART();
 
  char Temp_Instruction;

while(1)
{

  if(PIR1bits.RCIF == 1) // if the USART receive interrupt flag has been set
    { 
          Temp_Instruction = RCREG;

        if(Temp_Instruction == 'a')
        {
            LATBbits.LATB0 = 1;  // RB-0 to High 
            LATBbits.LATB1 = 1;  // RB-1 to High 

            RCREG = 0; //Empty register 
        }

        if(Temp_Instruction == 'b')
        {
            LATBbits.LATB0 = 0;  // RB-0 to Low 
            LATBbits.LATB1 = 0;  // RB-1 to Low

            RCREG = 0; //Empty register 
        }
    }
}

}

Also, is there a neater way to to this?

Thanks in advance.
 
I need to know what errors you are getting....

What compiler are you using I don't recognise " Configurate_USART();"...


Hi, I'm getting a syntax error on char Temp_Instruction;.

" Configurate_USART();" will go to this function that I made.

Code:
void Configurate_USART (void)
{

  //LEDs

  TRISB = 0xF0 ; // PORT B Setting: Set all the pins in port B to Output.

  // USART configuration

  TXSTAbits.TX9  = 0;    // 8-bit transmission
  TXSTAbits.TXEN = 1;    // Transmit enabled
  TXSTAbits.SYNC = 0;    // Asynchronous mode
  TXSTAbits.BRGH = 1;    // High speed

  RCSTAbits.SPEN = 1;    // Enable serial port - configures RX/DT and TX/CK pins as serial port pins
  RCSTAbits.RX9  = 0;    // 8-bit reception
  RCSTAbits.CREN = 1;    // Enable receiver

  BAUDCONbits.BRG16 = 0; // 8-bit baud rate generator

  SPBRGH = '129';        //calculated

  TRISCbits.RC6 = 0;    // make the TX pin a digital output
  TRISCbits.RC7 = 1;    // make the RX pin a digital input

}
 
This is the first time that I am using UART, so please let me know if it it not set correctly. Any help will be appreciated.
 
Are we to assume you have programmed the USART before and know it to be working (i.e. SPBRGH:SPBRG, SYNC bit, SPEN bit,RXDTP bit, RCIE bit, RX9 bit, CREN bit). You can easily test the USART is configured properly by writing back to the USART TX what you received on the RX.
 
Are we to assume you have programmed the USART before and know it to be working (i.e. SPBRGH:SPBRG, SYNC bit, SPEN bit,RXDTP bit, RCIE bit, RX9 bit, CREN bit). You can easily test the USART is configured properly by writing back to the USART TX what you received on the RX.

Is there a program that when sending data to the COM port, it will display the transmitted data?
 
You could use any terminal program (hyperterm, terraterm, procom, etc). The simplest way to start is by connecting the TX and RX pins on the cable. The terminal program would then echo back the characters you typed. Next you remove this connection on the cable and connect the cable to the PIC. You then write your PIC program so it echoes the received data back to transmit pin. You know you have everything configured properly on the PIC when you receive back what you typed.
 
You could use any terminal program (hyperterm, terraterm, procom, etc). The simplest way to start is by connecting the TX and RX pins on the cable. The terminal program would then echo back the characters you typed. Next you remove this connection on the cable and connect the cable to the PIC. You then write your PIC program so it echoes the received data back to transmit pin. You know you have everything configured properly on the PIC when you receive back what you typed.

And if I want to give instructions to the PIC when certain data is sent, it it done as the code attached above please? or is there another way?
 
Yes, your overall idea on how to give the instructions to the PIC based on received USART data is ok. But you first need to make sure the PIC is listening. If you can successfully loop back the received data, and send it back to the terminal you know the USART setup is correct; and then your only concern is really what you want to do. But it looks like at this point you can't say for sure your USART setup is correct.
 
You could use any terminal program (hyperterm, terraterm, procom, etc). The simplest way to start is by connecting the TX and RX pins on the cable. The terminal program would then echo back the characters you typed. Next you remove this connection on the cable and connect the cable to the PIC. You then write your PIC program so it echoes the received data back to transmit pin. You know you have everything configured properly on the PIC when you receive back what you typed.

And if I want to give instructions to the PIC when certain data is sent, it it done as the code attached above please? or is there another way?
 
Yes, your overall idea on how to give the instructions to the PIC based on received USART data is ok. But you first need to make sure the PIC is listening. If you can successfully loop back the received data, and send it back to the terminal you know the USART setup is correct; and then your only concern is really what you want to do. But it looks like at this point you can't say for sure your USART setup is correct.
Thanks for your replies. I did install hyperterm, but cannot really understand how to use it. Do I sent data from hyperterm itself or from Visual Studio? When I pressed SEND from hyperterm, a window popped up telling me to select a file. Isn't it just characters that you send?
 
When starting up Hyperterminal, you need to tell it to use a Com Port and configure it for the number of bits, baudrate etc to use. After that anything you type is sent out the Com Port you selected. If you want to see what you are typing, set local echo on. If your PIC is working as expected, you should see what you type being echoed back to you, or you should see it being repeated if you have local echo switched on in Hyperterminal :)
 
Thanks. So I'm assuming I have some problems :) or should that be :( When I typed A, it echoed Y. Than I typed C and Y and there was no echo back. After that, the program is not letting me type more characters. Do you know of any easy to follow tutorial on UART for PIC18F please? I spent the last three days trying to make this work.
 
more luck

Could you describe the whole system you are building? And post the full code also. "Syntax error" does not mean that the communication (rs232) is not working. It means that your code did not compile because of "Syntax error".

Also, is there a neater way to to this?
Yes, how deep you want to go? Do you take the red pill, or the blue pill?
 
Last edited:
Hi again.

I did the following myself:

Code:
// INCLUDE PIC18F4550 HEADERS (LIBRARIES) -------------------------------------------------------------------------------------------------------------------------------------------------------------

#include<p18f4550.h>
#include<delays.h>  //Library for delays IMPORTANT TO INCLUDE THIS LIBRARY FOR DELAYS ()()()()()()()()()()()()()()()()()()()()()()()()()()                         

// COMPILER DIRECTIVES FOR CHIP CONFIGURATION BITS ---------------------------------------------------------------------------------------------------------------------------------------------------------------------

#pragma config FOSC  = HSPLL_HS  // Since a 20MHz Xtal is used, set FOSC to HSPLL_HS (HS stands for high speed)
#pragma config PLLDIV = 5          // Divide the 20MHz by 5 to provide 4 MHz input to the 96 MHz PLL
#pragma config CPUDIV = OSC1_PLL2 // Divide 96 MHz PLL output by 2 to get 48 MHz system clock
#pragma config USBDIV = 2          // USB clock coming from 96 MHz PLL output is divided by 2
#pragma config FCMEN  = OFF      // Fail-Safe Clock Monitor disabled (this is used to stop operation when frequency gets out of tollerance--usually used for medical applications)
#pragma config IESO  = OFF      // Oscillator Switchover mode disabled
#pragma config PWRT  = OFF      // Enable Power-up timer (This causes the PIC to delay until full operating voltage is reached before the program starts)
#pragma config BOR    = ON        // Enable Brown-out reset (This automatically put the PIC in reset if the power coming into the chip isn't sufficient to work reliably, hence preventing malfunctions)
#pragma config VREGEN = ON        // Use internal USB voltage regulator from 5V to 3.3V
#pragma config WDT    = OFF      // Disable Watchdog timer (This is used so when the system see that it may not be working as expected, it automatically resets the PIC)
#pragma config MCLRE  = ON        // Enable MCLR Enable (MCLR is pin 1 of the PIC. When ground is applied it resets the PIC)
#pragma config LVP    = OFF      // Disable low voltage ICSP (This is another way to program the PIC. Since not used - Disable)
#pragma config ICPRT  = OFF      // Disable dedicated programming port (44-pin devices) (This is a Dedicated In-Circuit Debug/Programming Port)
#pragma config CP0    = OFF      // Disable code protection (Used to protect the program from being coppied)


// INITIALIZE FUNCTIONS (Prototyping the functions) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------


// MAIN FUNCTION -----------------------------------------------------------------------------------------------------------------------------------------------------------------------


void main(void)
{

    TRISB = 0xF0 ; // PORT B Setting: Set all the pins in port B to Output.
   

    TRISCbits.RC6 = 0; // make the TX pin a digital output
    TRISCbits.RC7 = 1; // make the RX pin a digital input

    SPBRG = 25;            // "25" calculated using formula from table 20-1 in the PIC18F4550 datasheet
    RCSTAbits.SPEN = 1;    // enable serial port (configures RX/DT and TX/CK pins as serial port pins)
    TXSTAbits.TXEN = 1;    // transmit enabled
    RCSTAbits.CREN = 1;    // enable receiver

    LATBbits.LATB0 = 0;  // RB-0 to High  //turn LEDs of on start up
    LATBbits.LATB1 = 0;  // RB-1 to High

while(1)
{
  if(PIR1bits.RCIF == 1) // if the USART receive interrupt flag has been set TO ZERO
  {
        if(PIR1bits.TXIF == 1) // check if the TXREG is empty
        {
            TXREG = RCREG; // echo received data back to sender
        }
  }
}

}

When using Hyperterminal, only the characters e, t, d, f, w, m, o, u, g, v are being echoed correctly. The rest are echoing other symbols. What can be causing this please? Is the baud rate correct for a 20MHz Crystal??

Please if someone can help me solve this it would be much appreciated. This is the forth day trying to make this work :(
 
Hi again.

I did the following code:

Code:
// INCLUDE PIC18F4550 HEADERS (LIBRARIES) -------------------------------------------------------------------------------------------------------------------------------------------------------------

#include<p18f4550.h>
#include<delays.h>  //Library for delays IMPORTANT TO INCLUDE THIS LIBRARY FOR DELAYS ()()()()()()()()()()()()()()()()()()()()()()()()()()                     

// COMPILER DIRECTIVES FOR CHIP CONFIGURATION BITS ---------------------------------------------------------------------------------------------------------------------------------------------------------------------

#pragma config FOSC  = HSPLL_HS  // Since a 20MHz Xtal is used, set FOSC to HSPLL_HS (HS stands for high speed)
#pragma config PLLDIV = 5          // Divide the 20MHz by 5 to provide 4 MHz input to the 96 MHz PLL
#pragma config CPUDIV = OSC1_PLL2 // Divide 96 MHz PLL output by 2 to get 48 MHz system clock
#pragma config USBDIV = 2          // USB clock coming from 96 MHz PLL output is divided by 2
#pragma config FCMEN  = OFF      // Fail-Safe Clock Monitor disabled (this is used to stop operation when frequency gets out of tollerance--usually used for medical applications)
#pragma config IESO  = OFF      // Oscillator Switchover mode disabled
#pragma config PWRT  = OFF      // Enable Power-up timer (This causes the PIC to delay until full operating voltage is reached before the program starts)
#pragma config BOR    = ON        // Enable Brown-out reset (This automatically put the PIC in reset if the power coming into the chip isn't sufficient to work reliably, hence preventing malfunctions)
#pragma config VREGEN = ON        // Use internal USB voltage regulator from 5V to 3.3V
#pragma config WDT    = OFF      // Disable Watchdog timer (This is used so when the system see that it may not be working as expected, it automatically resets the PIC)
#pragma config MCLRE  = ON        // Enable MCLR Enable (MCLR is pin 1 of the PIC. When ground is applied it resets the PIC)
#pragma config LVP    = OFF      // Disable low voltage ICSP (This is another way to program the PIC. Since not used - Disable)
#pragma config ICPRT  = OFF      // Disable dedicated programming port (44-pin devices) (This is a Dedicated In-Circuit Debug/Programming Port)
#pragma config CP0    = OFF      // Disable code protection (Used to protect the program from being coppied)


// INITIALIZE FUNCTIONS (Prototyping the functions) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------


// MAIN FUNCTION -----------------------------------------------------------------------------------------------------------------------------------------------------------------------


void main(void)
{

    TRISB = 0xF0 ; // PORT B Setting: Set all the pins in port B to Output.


    TRISCbits.RC6 = 0; // make the TX pin a digital output
    TRISCbits.RC7 = 1; // make the RX pin a digital input

    SPBRG = 25;            // "25" calculated using formula from table 20-1 in the PIC18F4550 datasheet
    RCSTAbits.SPEN = 1;    // enable serial port (configures RX/DT and TX/CK pins as serial port pins)
    TXSTAbits.TXEN = 1;    // transmit enabled
    RCSTAbits.CREN = 1;    // enable receiver

    LATBbits.LATB0 = 0;  // RB-0 to High  //turn LEDs of on start up
    LATBbits.LATB1 = 0;  // RB-1 to High

while(1)
{
  if(PIR1bits.RCIF == 1) // if the USART receive interrupt flag has been set TO ZERO
  {
        if(PIR1bits.TXIF == 1) // check if the TXREG is empty
        {
            TXREG = RCREG; // echo received data back to sender
        }
  }
}

}

When using Hyperterminal, only the characters e, t, d, f, w, m, o, u, g, v are being echoed correctly. The rest are echoing other symbols. What can be causing this please? Is the baud rate correct for a 20MHz Crystal??

Please if someone can help me solve this it would be much appreciated. This is the fourth day trying to make this work :( but at least I did some improvement because yesterday only the characters w, m, o, u were being echoed correctly.
 
if(PIR1bits.TXIF == 1) // check if the TXREG is empty

This will not work.... I found this out myself a while ago.... I will still drop characters.

Use this..
C:
while(!TXSTAbits.TRMT );// Wait until empty
TXREG = RCREG;
 
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