A dsPIC program to display bytes received via serial link

I wrote the following short program for the dsPIC30F4011 microcontroller to record a sequence of bytes received via serial link (UART 2) and then print the byte values and the corresponding text string via UART 1. I was using this to verify that another program I had written (SerialSend) was working correctly. SerialSend is a command line application for Windows which is used to transmit arbitrary sequences of bytes via a serial port.

//
// dsPIC30F4011 program to record bytes received via UART 2
// and then print the byte values and text string via UART 1
//
// Written by Ted Burke - last updated 16-4-2013
//

#include <xc.h>
#include <stdio.h>
 
// Configuration settings
_FOSC(CSW_FSCM_OFF & FRC_PLL16); // Fosc=16x7.5MHz, i.e. 30 MIPS
_FWDT(WDT_OFF);                  // Watchdog timer off
_FBORPOR(MCLR_DIS);              // Disable reset pin

// Function prototype for Timer 1 interrupt service routine
void __attribute__((__interrupt__, __auto_psv__)) _T1Interrupt(void);

int n = 0;
unsigned char buf[100];

int main(void)
{
	// Setup UART 1
	U1BRG = 48;            // 38400 baud @ 30 MIPS
	U1MODEbits.UARTEN = 1; // Enable UART
	
	// Setup UART 2
	U2BRG = 48;            // 38400 baud @ 30 MIPS
	U2MODEbits.UARTEN = 1; // Enable UART

	// Configure Timer 1
	// TMR1 is set to zero whenever a byte is received
	// or whenever the buffer is empty. Whenever TMR1
	// reaches PR1, the Timer 1 ISR prints whatever
	// bytes are in the buffer. This creates a timeout,
	// such that when bytes are received, they are stored
	// in the buffer, but when no bytes are received for
	// 100ms, the buffer data is printed.
	PR1 = 46875;          // Set the Timer 1 period to 100ms
	TMR1 = 0;             // Reset Timer 1 counter
	IEC0bits.T1IE = 1;    // Enable Timer 1 interrupt
	T1CONbits.TCKPS = 2;  // Prescaler (0=1:1, 1=1:8, 2=1:64, 3=1:256)
	T1CONbits.TON = 1;    // Turn on Timer 1

	_TRISD0 = 0; // Make RD0 a digital output

	while(1)
	{
		// Don't let TMR1 increase unless bytes are in buffer
		if (n == 0) TMR1 = 0;

		// Check if any characters were received via UART
		if (U2STAbits.URXDA == 1)
		{
			// Store received byte and increment byte counter
			buf[n++] = U2RXREG;
			TMR1 = 0;
		}
	}

	return 0;
}

// Timer 1 interrupt service routine prints the buffer contents.
// This runs when there are bytes stored in the buffer, but none
// have been received for 100ms.
void __attribute__((__interrupt__, __auto_psv__)) _T1Interrupt(void)
{
	int m;

	// Clear Timer 1 interrupt flag
	IFS0bits.T1IF = 0;

	// Print bytes as numbers in hex format
	for (m=0 ; m<n ; ++m) printf("%02x ", buf[m]);

	// Print the same bytes again as a text string
	buf[n] = '\0';
	printf("\n%s\n", buf);

	// Reset the buffer byte count
	n = 0;
}

I compiled the program above with Microchip’s XC16 C compiler using the following simple build script.

xc16-gcc main.c -mcpu=30F4011 -Wl,--script=p30F4011.gld
if errorlevel 0 xc16-bin2hex a.out

To use the build script, just create a new folder, save the C program above in the folder as “main.c”, save the build script above as “build.bat” in the same folder, and then open a command window and type “build.bat”.

Example

The following screenshot shows SerialSend running twice in a command window. The serial device used (COM22) is a USB-to-serial converter which is connected to the Tx and Rx pins of UART 2 on the dsPIC.

The following screenshot shows the UART tool window in the PICkit 2 software application. The PICkit 2 hardware is connected to the Tx and Rx pins of UART 1. The byte sequences sent in the previous screenshot have been received by the dsPIC on UART 2 and, after a 100ms timeout, printed out via UART 1 and displayed in the UART tool.