Cannot send or receive data through UART on PIC24F development board - c

Question

I am trying to upload a simple UART testing program to a PIC24F Curiosity Board using MPLAB X and validate data transmission using TeraTerm. This evaluation board uses a PIC24FJ128GA204 microcontroller. I have made sure to set the serial port configuration on TeraTerm as it is defined in the program.
For data transmission, I am using a USB to RS-232 UART cable connected to my desktop. I have double checked my cable connections and they are as defined in the program. I am not using the +5 Vcc on the cable and I have connected the cable to ground, but I have tried connected and disconnected ground.
Currently no data will be transmitted, although I have noticed that when I program the board, sometimes TeraTerm will display some random values, which I am not sure if that implies there is a connection capable of data transmission or it is just random noise.
Currently, my UART initialization is as follows:
#include <xc.h>
#define U_ENABLE 0x8008 // enable UART, BREGH=1, 1 stop, 8 data bits, no parity, RTS/CTS flow control
#define U_TX 0x0400 // enable transmission, clear all flags
#define _XTAL_FREQ 8000000 //set to internal oscillator frequency
//** UART2 RS232 asynchronous communication demonstration
void initialize_UART(void) {
U1BRG = 104; // initialize the baud rate generator to 104, an equivalent value of 9524
U1MODE = U_ENABLE; // initialize the UART module
U1STA = U_TX; // enable the receiver
//****CONFIGURING FOR UART****
//MICROCONTROLLER PIN || UART WIRE
//RP0/RB0 = U1RX
//RP1/RB1 = U1CTS (Clear to send)
//RP2/RB2 = U1TX
//RP3/RB3 = UR1RTS ()
// Unlock Registers (per MCU data sheet)
asm volatile ("MOV #OSCCON, w1 \n"
"MOV #0x46, w2 \n"
"MOV #0x57, w3 \n"
"MOV.b w2, [w1] \n"
"MOV.b w3, [w1] \n"
"BCLR OSCCON, #6") ;
// Configure Input Functions (Table 11-3 in Datasheet)
// Assign U1RX To Pin RP0
//RPINR
RPINR18bits.U1RXR = 0;
// Assign U1CTS To Pin RP1
RPINR18bits.U1CTSR = 1;
// Configure Output Functions (Table 11-4 in Datasheet)
// Assign U1TX To Pin RP2
RPOR1bits.RP2R = 3;
// Assign U1RTS To Pin RP3
RPOR1bits.RP3R = 4;
// Lock Registers
asm volatile ("MOV #OSCCON, w1 \n"
"MOV #0x46, w2 \n"
"MOV #0x57, w3 \n"
"MOV.b w2, [w1] \n"
"MOV.b w3, [w1] \n"
"BSET OSCCON, #6") ;
}
My function for sending data through UART:
char UART_send_char(char a)
{
while (PORTBbits.RB1 == 1); //wait for clear to send
while (U1STAbits.UTXBF); //wait while Tx buffer is full
U1TXREG = a;
return a;
}
How I am testing the function in main():
int main(void)
{
TRISA = 0;
// init the UART1 serial port
initialize_UART();
// main loop
while (1)
{
PORTAbits.RA10 = 1; //for debugging purposes
UART_send_char('>');
}
}
This program should continuously send the character ">" to the TeraTerm console, but instead I receive nothing. RA10 is connected to an LED, which does light up so I know the program has entered the main loop, but no data is being sent. I have the configuration bits set to the internal oscillator which operates at 8 MHz and have disabled the PLL. BREGH is set to 1, so I have used the respective formula for the Baud Rate Generator given in the datasheet on page 247 with an Fcy value of 8 MHz/2.
I am new to programming MCUs and have spent some hours trying to fix this to no avail, so any help would be much appreciated.

Answer 1

Here is a complete single file application that runs on the DM240004 PIC24F Curiosity Development Board using a MikroElektronical USB UART click.
/*
* https://github.com/dsoze1138/24FJ128GA204_DM240004
*
* File: main.c
* Author: dan1138
* Target: PIC24FJ128GA204
* Compiler: XC16 v1.60
* IDE: MPLABX v5.45
*
* Created on November 24, 2020, 12:02 PM
*
* PIC24FJ128GA204
* +----------------+ +--------------+ +-----------+ +--------------+
* J4_MOSI <> 1 : RB9/RP9 : LED2 <> 12 : RA10 : J4_SDA <> 23 : RB2/RP2 : X2-32KHZ <> 34 : RA4/SOSCO :
* RGB_G <> 2 : RC6/RP22 : <> 13 : RA7 : J4_SCL <> 24 : RB3/RP3 : LED1 <> 35 : RA9 :
* RGB_B <> 3 : RC7/RP23 : <> 14 : RB14/RP14 : POT <> 25 : RC0/RP16 : J4_CS <> 36 : RC3/RP19 :
* S2 <> 4 : RC8/RP24 : <> 15 : RB15/RP15 : <> 26 : RC1/RP17 : J4_SCK <> 37 : RC4/RP20 :
* S1 <> 5 : RC9/RP25 : GND -> 16 : AVSS : <> 27 : RC2/RP18 : RGB_R <> 38 : RC5/RP21 :
* 3v3 <> 6 : VBAT : 3v3 -> 17 : AVDD : 3v3 -> 28 : VDD : GND -> 39 : VSS :
* 10uF -> 7 : VCAP : ICD_VPP -> 18 : MCLR : GND -> 29 : VSS : 3v3 -> 40 : VDD :
* <> 8 : RB10/RP11/PGD2 : J4_AN <> 19 : RA0/AN0 : <> 30 : RA2/OSCI : J4_RX <> 41 : RB5/RP5/PGD3 :
* <> 9 : RB11/RP11/PGC2 : J4_RST <> 20 : RA1/AN1 : <> 31 : RA3/OSCO : J4_TX <> 42 : RB6/RP6/PGC3 :
* <> 10 : RB12/RP12 : ICD_PGD <> 21 : RB0/RP0/PGD1 : <> 32 : RA8 : <> 43 : RB7/RP7 :
* <> 11 : RB13/RP13 : ICD_PGC <> 22 : RB1/RP1/PGC1 : X2-32KHZ <> 33 : RB4/SOSCI : J4_MISO <> 44 : RB8/RP8 :
* +----------------+ +--------------+ +-----------+ +--------------+
* TQFP-44
*
* Description:
*
* Bare metal initialization of the DM240004 Curiosity Board
*
* Setup the system oscillator for 32MHz using the internal FRC and the 4x PLL.
* Turn on the 32.768KHz secondary oscillator.
* Use UART1 and printf to send a message as 9600 baud.
* Flash LED2 on for 500 milliseconds then off for 500 milliseconds.
*
*/
// CONFIG4
#pragma config DSWDTPS = DSWDTPS1F // Deep Sleep Watchdog Timer Postscale Select bits (1:68719476736 (25.7 Days))
#pragma config DSWDTOSC = LPRC // DSWDT Reference Clock Select (DSWDT uses LPRC as reference clock)
#pragma config DSBOREN = OFF // Deep Sleep BOR Enable bit (DSBOR Disabled)
#pragma config DSWDTEN = OFF // Deep Sleep Watchdog Timer Enable (DSWDT Disabled)
#pragma config DSSWEN = OFF // DSEN Bit Enable (Deep Sleep operation is always disabled)
#pragma config PLLDIV = PLL4X // USB 96 MHz PLL Prescaler Select bits (4x PLL selected)
#pragma config I2C1SEL = DISABLE // Alternate I2C1 enable bit (I2C1 uses SCL1 and SDA1 pins)
#pragma config IOL1WAY = OFF // PPS IOLOCK Set Only Once Enable bit (The IOLOCK bit can be set and cleared using the unlock sequence)
// CONFIG3
#pragma config WPFP = WPFP127 // Write Protection Flash Page Segment Boundary (Page 127 (0x1FC00))
#pragma config SOSCSEL = ON // SOSC Selection bits (SOSC circuit selected)
#pragma config WDTWIN = PS25_0 // Window Mode Watchdog Timer Window Width Select (Watch Dog Timer Window Width is 25 percent)
#pragma config PLLSS = PLL_FRC // PLL Secondary Selection Configuration bit (PLL is fed by the on-chip Fast RC (FRC) oscillator)
#pragma config BOREN = OFF // Brown-out Reset Enable (Brown-out Reset Disabled)
#pragma config WPDIS = WPDIS // Segment Write Protection Disable (Disabled)
#pragma config WPCFG = WPCFGDIS // Write Protect Configuration Page Select (Disabled)
#pragma config WPEND = WPENDMEM // Segment Write Protection End Page Select (Write Protect from WPFP to the last page of memory)
// CONFIG2
#pragma config POSCMD = NONE // Primary Oscillator Select (Primary Oscillator Disabled)
#pragma config WDTCLK = LPRC // WDT Clock Source Select bits (WDT uses LPRC)
#pragma config OSCIOFCN = ON // OSCO Pin Configuration (OSCO/CLKO/RA3 functions as port I/O (RA3))
#pragma config FCKSM = CSECMD // Clock Switching and Fail-Safe Clock Monitor Configuration bits (Clock switching is enabled, Fail-Safe Clock Monitor is disabled)
#pragma config FNOSC = FRC // Initial Oscillator Select (Fast RC Oscillator (FRC))
#pragma config ALTCMPI = CxINC_RB // Alternate Comparator Input bit (C1INC is on RB13, C2INC is on RB9 and C3INC is on RA0)
#pragma config WDTCMX = WDTCLK // WDT Clock Source Select bits (WDT clock source is determined by the WDTCLK Configuration bits)
#pragma config IESO = OFF // Internal External Switchover (Disabled)
// CONFIG1
#pragma config WDTPS = PS32768 // Watchdog Timer Postscaler Select (1:32,768)
#pragma config FWPSA = PR128 // WDT Prescaler Ratio Select (1:128)
#pragma config WINDIS = OFF // Windowed WDT Disable (Standard Watchdog Timer)
#pragma config FWDTEN = OFF // Watchdog Timer Enable (WDT disabled in hardware; SWDTEN bit disabled)
#pragma config ICS = PGx1 // Emulator Pin Placement Select bits (Emulator functions are shared with PGEC1/PGED1)
#pragma config LPCFG = OFF // Low power regulator control (Disabled - regardless of RETEN)
#pragma config GWRP = OFF // General Segment Write Protect (Write to program memory allowed)
#pragma config GCP = OFF // General Segment Code Protect (Code protection is disabled)
#pragma config JTAGEN = OFF // JTAG Port Enable (Disabled)
/*
* Defines for system oscillator frequency.
* Make sure that the PIC initialization selects this frequency.
*/
#define FSYS (32000000ul)
#define FCY (FSYS/2ul)
/*
* Target specific Special Function Register definitions
*/
#include <xc.h>
/*
* Standard header files
*/
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
/*
* Initialize this PIC
*/
void PIC_Init(void)
{
uint16_t ClockSwitchTimeout;
/*
* Disable all interrupt sources
*/
__builtin_disi(0x3FFF); /* disable interrupts for 16383 cycles */
IEC0 = 0;
IEC1 = 0;
IEC2 = 0;
IEC3 = 0;
IEC4 = 0;
IEC5 = 0;
IEC6 = 0;
IEC7 = 0;
__builtin_disi(0x0000); /* enable interrupts */
INTCON1bits.NSTDIS = 1; /* Disable interrupt nesting */
/*
* At Power On Reset the configuration words set the system clock
* to use the FRC oscillator. At this point we need to enable the
* PLL to get the system clock running at 32MHz.
*
* Clock switching on the 24FJ family with the PLL can be a bit tricky.
*
* First we need to check if the configuration words enabled clock
* switching at all, then turn off the PLL, then setup the PLL and
* finally enable it. Sounds simple, I know. Make sure you verify this
* clock setup on the real hardware.
*/
if(!OSCCONbits.CLKLOCK) /* if primary oscillator switching is unlocked */
{
/* Select primary oscillator as FRC */
__builtin_write_OSCCONH(0b000);
/* Request switch primary to new selection */
__builtin_write_OSCCONL(OSCCON | (1 << _OSCCON_OSWEN_POSITION));
/* wait, with timeout, for clock switch to complete */
for(ClockSwitchTimeout=10000; --ClockSwitchTimeout && OSCCONbits.OSWEN;);
CLKDIV = 0x0000; /* set for FRC clock 8MHZ operations */
/* Select primary oscillator as FRCPLL */
__builtin_write_OSCCONH(0b001);
/* Request switch primary to new selection */
__builtin_write_OSCCONL(OSCCON | (1 << _OSCCON_OSWEN_POSITION));
/* ALERT: This may be required only when the 96MHz PLL is used */
CLKDIVbits.PLLEN = 1;
/* wait, with timeout, for clock switch to complete */
for(ClockSwitchTimeout=10000; --ClockSwitchTimeout && OSCCONbits.OSWEN;);
/* wait, with timeout, for the PLL to lock */
for(ClockSwitchTimeout=10000; --ClockSwitchTimeout && !OSCCONbits.LOCK;);
/* at this point the system oscillator should be 32MHz */
}
/* Turn on Secondary Oscillation Amplifier */
__builtin_write_OSCCONL(OSCCON | (1 << _OSCCON_SOSCEN_POSITION));
/* Turn off all analog inputs */
ANSA = 0;
ANSB = 0;
ANSC = 0;
}
/*
* WARNING: Not a portable function.
* Maximum delay 16384 instruction cycles.
* At 16 MIPS this is 1024 microseconds.
*
* Minimum 1MHz instruction cycle clock.
*/
void delay_us(unsigned short delay)
{
if (delay > (uint16_t)(16383.0 / (FCY/1E6)))
{
asm(" repeat #16383\n"
" clrwdt \n"
::);
}
else
{
asm(" repeat %0 \n"
" clrwdt \n"
:: "r" (delay*(uint16_t)(FCY/1000000ul)-1));
}
}
/*
* WARNING: Not a portable function.
* Maximum 16MHz instruction cycle clock.
* Minimum 8Khz instruction cycle clock.
*/
void delay_ms(unsigned long delay)
{
if(delay)
{
asm("1: repeat %0 \n"
" clrwdt \n"
" sub %1,#1 \n"
" subb %d1,#0 \n"
" bra nz,1b \n"
:: "r" (FCY/1000ul-6ul), "C" (delay));
}
}
/*
* Initialize the UART
*/
void UART_Init(void)
{
/**
Set the UART1 module to run at 9600 baud with RB6 as TX out and RB5 as RX in.
*/
TRISBbits.TRISB6 = 0;
LATBbits.LATB6 = 1;
__builtin_write_OSCCONL(OSCCON & ~_OSCCON_IOLOCK_MASK); // unlock PPS
RPINR18bits.U1RXR = 0x0005; //RB5->UART1:U1RX
RPOR3bits.RP6R = 0x0003; //RB6->UART1:U1TX
__builtin_write_OSCCONL(OSCCON | _OSCCON_IOLOCK_MASK); // lock PPS
// STSEL 1; IREN disabled; PDSEL 8N; UARTEN enabled; RTSMD disabled; USIDL disabled; WAKE disabled; ABAUD disabled; LPBACK disabled; BRGH enabled; URXINV disabled; UEN TX_RX;
// Data Bits = 8; Parity = None; Stop Bits = 1;
U1MODE = (0x8008 & ~(1<<15)); // disabling UARTEN bit
// UTXISEL0 TX_ONE_CHAR; UTXINV disabled; URXEN disabled; OERR NO_ERROR_cleared; URXISEL RX_ONE_CHAR; UTXBRK COMPLETED; UTXEN disabled; ADDEN disabled;
U1STA = 0x00;
// BaudRate = 9600; Frequency = 16000000 Hz; U1BRG 416;
U1BRG = 0x1A0;
// ADMADDR 0; ADMMASK 0;
U1ADMD = 0x00;
// T0PD 1 ETU; PTRCL T0; TXRPT Retransmits the error byte once; CONV Direct; SCEN disabled;
U1SCCON = 0x00;
// TXRPTIF disabled; TXRPTIE disabled; WTCIF disabled; WTCIE disabled; PARIE disabled; GTCIF disabled; GTCIE disabled; RXRPTIE disabled; RXRPTIF disabled;
U1SCINT = 0x00;
// GTC 0;
U1GTC = 0x00;
// WTCL 0;
U1WTCL = 0x00;
// WTCH 0;
U1WTCH = 0x00;
U1MODEbits.UARTEN = 1; // enabling UART ON bit
U1STAbits.UTXEN = 1;
}
uint8_t UART1_Read(void)
{
while(!(U1STAbits.URXDA == 1));
if ((U1STAbits.OERR == 1))
{
U1STAbits.OERR = 0;
}
return U1RXREG;
}
void UART1_Write(uint8_t txData)
{
while(U1STAbits.UTXBF == 1);
U1TXREG = txData; // Write the data byte to the USART.
}
bool UART1_IsRxReady(void)
{
return U1STAbits.URXDA;
}
bool UART1_IsTxReady(void)
{
return ((!U1STAbits.UTXBF) && U1STAbits.UTXEN );
}
bool UART1_IsTxDone(void)
{
return U1STAbits.TRMT;
}
int __attribute__((__section__(".libc.write"))) write(int handle, void *buffer, unsigned int len)
{
unsigned int i;
for (i = len; i; --i)
{
UART1_Write(*(char*)buffer++);
}
return(len);
}
/*
* Main Application
*/
int main(void)
{
/*
* Application initialization
*/
PIC_Init();
UART_Init();
/* Set RA10 for output to drive LED2 */
LATAbits.LATA10 = 0;
TRISAbits.TRISA10 = 0;
printf("\r\nPIC24FJ128GA204 built on " __DATE__ " at " __TIME__ " Start\r\n");
/*
* Application process loop
*/
for(;;)
{
LATAbits.LATA10 ^= 1;
delay_ms(500);
}
return 0;
}
I suspect that your problem may be trying to implement hardware handshaking with the RTS/CTS signaling.
Try to get the serial data transmit from the PIC to the PC working at a slow baud rate first.
And another thing is that RB0 and RB1 are used to program (and debug) the PIC24FJ128GA204. The onboard In-Circuit-Serial-Programmer can interfere with using these pins for other functions. In a debug session they cannot be used by the application at all.