Electronic – Reception without interrupt in USART of PIC18

picuart

I would like to know how to receive data without interrupts in the PIC18 controller.
After setting the USART settings and baud rating, what things must be done so that USART receives properly without use of interrupts?

I'm using it in asynchronous mode. I have tested the transmission process successfully by checking the transmit bit in the USART TXSTAT register.

I have seen using a TRMT bit for tracking status of transmission in the EUSART register. But what can be used for receiving?

I did not see a similar pin in the RXSTAT register for asynchronous mode.

Best Answer

The trick is that when interrupts are disabled the RCIF interrupt flag bit is still set, it just doesn't generate an interrupt. Reading a byte from the RCREG receiver data register clears the bit on most PIC18 chips I believe so that leaves at simple as:

if (PIR1.RCIF)        // We have a byte
   new_data = RCREG;  // Do something with it

Another thing is that if you get an overflow error because another byte arrives before you've read the first you'll also want something like the following to clear the error condition:

if (RCSTA.OERR)       // We had an overflow error
{
    RCSTA.CREN = 0;   // Clear the CREN bit to reset it
    RCSTA.CREN = 1;   // Re-enable continuous receive
}

The above will probably vary in syntax depending on the compiler you're using but hopefully gives you the general idea.

Related Solutions

Electronic – PIC18 USART problem

The problem here is that Microchip sneakily defaulted the CPUDIV to /4 meaning the internal clock of the PIC was running at a quarter of the expected frequency - thus the calculations were all wrong.

It took some time to figure this out, but setting

#pragma config CPUDIV = NOCLKDIV

appears to fixed the problem. Also, because I am using a MAX232 linked to the output I have to invert the signals:

baudUSART(BAUD_IDLE_CLK_LOW & 
          BAUD_AUTO_OFF & 
          BAUD_8_BIT_RATE & 
          BAUD_IDLE_RX_PIN_STATE_HIGH);

OpenUSART (USART_TX_INT_OFF &
           USART_RX_INT_OFF &
           USART_ASYNCH_MODE &
           USART_EIGHT_BIT &
           USART_CONT_RX &
           USART_ADDEN_OFF &
           USART_BRGH_HIGH, 103);

Electronic – PIC18 USART Interrupt for reception, doesn’t trigger

Every processor has its own special interrupt-handling quirks.

Microchip's PIC18F4331 page has links to an errata document and the PIC18F4331 datasheet. In particular, the datasheet has some good tips in section 20 "Enhanced universal synchronous asynchronous receiver transmitter (EUSART)" and even more particularly, the 3 steps listed in section 20.0 and the 10 steps of "To set up an Asynchronous Reception" in section 20.3.2.

I've changed a few things that look like they might help:

// WARNING: untested code
int main(void){

//***********************Initializing Values****************************//
unsigned int ResultADC, FLAG; 
unsigned char temp, idle; //High Byte result store, 8bits long

//***********************ADC and SPI Settings****************************//

Initialize_control();    //Initialize Control Configuration Pins
InitializeADC();         //Initialize ADC in Continuous Mode
USART_initialize();      //Initialize USART module
InitializeMasterSPI();   //Initialize SPI module

//***********************ADC Capture and Output to SPI******************//

  while(1){             //While ADC buffer has something

    //Enable transmission
     TXREG = 0xff; //Debugger

     while(!TXSTAbits.TRMT);//wait while TSR is full

     TXREG = 0x0; //Debugger

     while(!TXSTAbits.TRMT);//wait while TSR is full

  }
  return 0;
}

//////////////////INTERRUPT SERVICE ROUTINE/////////////////

static void interrupt isr(void){
    // The PIC hardware has already disabled global interrupts
    // by the time it starts executing the ISR,
    // so there's no need to do "PIE1bits.RCIE  = 0;".

int count;

//Read USART data
//PIR1bits.RCIF;//Data has been passed to RCREG
RX_Data[count] = RCREG; //Read RX register
count++;
//Reading RCREG automatically clears the RX flag.
// so there's no need to do "PIR1bits.RCIF = 0;".
// Q: How to read more than 1 byte?
// A: FIGURE 20-5 of the datasheet
// Implies that there's only a 1 byte buffer.
// Therefore, to read more than 1 byte, we must:
// pull the current byte out of the hardware buffer,
// store it in a software buffer RX_Data[] in RAM,
// then return to normal background main loop
// until the next byte in the message
// triggers another interrupt.

// Would it be better to do the following in the main loop?
  if (count==3){
    //Use data for control
    Control_Arduino(RX_Data);
    count = 0;
  }

/*
The datasheet p. 229 is a little confusing about
whether "CREN" should be set (step 5) or cleared (step 9).
p. 219 which clearly seems to say CREN should be set.
But maybe it needs to be cleared to flush out any errors,
and then be set?
Are the following 2 lines really necessary?
*/
RCSTAbits.CREN = 0; //clear error (if any)
RCSTAbits.CREN = 1; //Enables Receiver

// the PIC hardware enables global interrupts
// automatically during the return-from-interrupt,
// so there's no need to do a "PIE1bits.RCIE  = 1;"
// See the datasheet section 10.0: "Interrupts" for details.

}

//**********************Functions****************************//

void USART_initialize(void){

//Configuration TX and RX pins
// *normally* we use a "0" to indicate "output",
// but the TX output pin is different, see p. 217 of datasheet
TRISCbits.RC6 = 1; //TX output
TRISCbits.RC7 = 1; //RX input

//TXSTA: Transmit Status and Control Register
TXSTAbits.SYNC = 0; //Asynchronous mode
TXSTAbits.TX9 = 0; //8bit transmission
TXSTAbits.BRGH = 1; //Set HIGH Baud rate
TXSTAbits.TXEN = 1; //Enable transmitter
TXSTAbits.SENDB = 0; //Disable break

//RCSTA: Receive Status and Control Register
RCSTAbits.SPEN = 1; //Serial Port enabled
RCSTAbits.RX9 = 0; //8bit reception
RCSTAbits.CREN = 1; //Enables Receiver

//Test bits
//    RCSTAbits.FERR = 0; //No framing error, cleared by reading
//    RCSTAbits.OERR = 0; //No Overrun error, cleared by clearing CREN
                      //Disable receiver CREN 0

//BAUDCON Control register
BAUDCONbits.BRG16 = 1;  //16bit baud rate generator
SPBRG = 0xCF;           // Set to 19200 baud rate, 12Mhz, High Speed, BRG16
//Test bits
//    BAUDCONbits.RCIDL = 0; //Receive in progress

// USART interrupts configuration
RCONbits.IPEN   = 1; // ENABLE interrupt priority
// (p. 4 of http://www.gooligum.com.au/tutorials/midrange/PIC_Mid_C_3.pdf )
ei(); // same as INTCONbits.GIE  = 1; // ENABLE interrupts
INTCONbits.PEIE = 1; // ENable peripheral interrupts.
PIE1bits.RCIE   = 1; // ENABLE USART receive interrupt
PIE1bits.TXIE   = 0; // disable USART TX interrupt

// make sure the RX flag is clear
    PIR1bits.RCIF = 0;
}

Other code online:

"AN944: Using the EUSART on the PIC16F688" http://www.gooligum.com.au/tutorials/midrange/PIC_Mid_C_3.pdf https://forum.sparkfun.com/viewtopic.php?t=7542 http://panteltje.com/panteltje/pic/scope_pic/ http://www.microchip.com/forums/m411875.aspx http://www.enmcu.com/guides/autobaudratebasedoneusartmodule

Tell us if you ever figure out the real problem, OK?

Best Answer

Related Solutions

Electronic – PIC18 USART problem

Electronic – PIC18 USART Interrupt for reception, doesn’t trigger

Related Topic