PIC32 UART: U1RXREG Register Never Contains Any Values Other Than 0 - c

Question

I've attached an image showing my oscilloscope readout which is from the code below. Context: I have a Pi and a PIC which need to communicate through UART connection. I've implemented my own flow control which can be seen in the image attached [RTS = Yellow Trace, CTS = Blue Trace, Rx = Green Trace]. The code runs through and is caught in the final switch case statement which turns on an LED. But when i debug the code, no values (well the only value which is read is zero) are read in. At first i thought that i'd configured my PIC clock wrong (which is used to derive the baud rate), but i don't think this is the case. Second i through the FIFO buffer was full of zeros only and considering that i'm sending only four packets of information to the PIC, and my FIFO is 4 registers deep that this was the reason why non of the information was appearing. So i executed a code which removes the dummy bytes but this did not work.
All that is received:
0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0><0> etc
I got the right settings selected: baud rate: 9600 data bits: 8 parity: none stop bits: 1
If anyone is willing to spend some time looking at my code, can you see any obvious errors?
https://i.stack.imgur.com/aQoAL.jpg
Minimum Reproducible Example
# include <xc.h>
# include <math.h>
# include <stdio.h>
# include <stdio.h>
//Configuration Bits
#pragma config FNOSC = FRCPLL // Internal Fast RC Oscillator (8MHz)
#pragma config FPLLIDIV = DIV_2 // Divide FRC before PLL (Now 4MHz)
#pragma config FPLLMUL = MUL_20 // PLL Multiply (Now 80MHz)
#pragma config FPLLODIV = DIV_2 // Divide After PLL (Now 40MHz)
#pragma config FPBDIV = DIV_1 // Pheripheral Bus Clock (At 40KHz)
#pragma config FWDTEN = OFF // Watchdog Timer Disabled
#pragma config ICESEL = ICS_PGx2 // ICE/ICD Comm Channel Select
#pragma config JTAGEN = OFF // Disable JTAG
#pragma config FSOSCEN = OFF // Disable Secondary Oscillator
//*****************************UART Functions***********************************
void UART_Config (void) // Baude Rate of 9600, 8-Bit Data , 1 Stop Bit
{
U1MODEbits.BRGH = 0;
U1BRG = 259; //U1BRG = (40M/ (16 * 9.6k))) - 1
U1MODEbits.SIDL = 0; // Continue operation in SLEEP mode
U1MODEbits.IREN = 0; // IrDA is disabled
U1MODEbits.RTSMD = 0; // U1RTS pin is in Flow Control mode
U1MODEbits.UEN = 0b00; // U1TX, U1RX are enabled
U1MODEbits.WAKE = 1; // Wake-up enabled
U1MODEbits.LPBACK = 0; // Loopback mode is disabled
U1MODEbits.RXINV = 0; // U1RX IDLE state is '1'
U1MODEbits.PDSEL = 0b00; // 8-bit data, no parity
U1MODEbits.STSEL = 0; // 1 stop bit
U1STAbits.UTXINV = 0; // U1TX IDLE state is '1'
U1MODEbits.ON = 1; // UART1 is enabled
U1STAbits.URXEN = 1; // UART1 receiver is enabled
U1STAbits.UTXEN = 1; // UART1 transmitter is enabled
}
void Send_UART_Data(unsigned int c) // PIC Sending Data for Pi to Read
{
U1STAbits.UTXEN = 1; // Make sure transmitter is enabled
// while(CTS) // Optional CTS (Clear to Send) use
while(U1STAbits.UTXBF); // Wait while buffer is full
U1TXREG = c; // Transmit character
}
int Read_UART_Data (void) // PIC Reading Sent Data from Pi
{
int c;
while(!U1STAbits.URXDA) // Wait for information to be received
c = (int)U1RXREG; // Convert Character to Value
return c;
}
ADC_To_UART (unsigned int ADC)
{
unsigned int temp_A = 0x00;
unsigned int temp_B = 0x00;
// Splitting a 10 Bit Word Into 2 Bytes [aa aaaa aabb]
// Start Bit = 1 , Stop Bit = 0
// UART Transmission Pattern [1 aaaa aaaa 0 0000 00 bb]
temp_A = ADC >> 2; // MSB(8 Bits) ~ ADC[9:2] [aaaa aaaa]
temp_B = ADC & 0x003; // LSB(2 Bits) ~ ADC[1:0] [0000 00bb]
Send_UART_Data(temp_A);
Send_UART_Data(temp_B);
}
[enter image description here][1]
//*********************Enumerated Variable Declaration**************************
//Program Flow Control
enum Comm_State {Phase1A, Phase1B, Phase1C, Phase1D, Phase1E, Phase2A, Phase2B, Phase2C, Phase2D, Phase2E, Phase2F, Phase2G};
//******************************************************************************
//********************************MAIN******************************************
int main( )
{
//***************************Configuration**********************************
// I/O Definitions
#define UART_TRIS_RX TRISBbits.TRISB13 // UART RX - Reciever Pin (PPS)
#define UART_TRIS_TX TRISBbits.TRISB15 // UART TX - Transmission Pin (PPS)
#define UART_TRIS_CTS_PIC TRISAbits.TRISA4 // UART CTS_1 - Clear to Send - Output [CTS PIC]
#define UART_TRIS_RTS_PIC TRISBbits.TRISB4 // UART RTS_1 - Ready to Send - Output [RTS PIC]
#define UART_TRIS_CTS_PI TRISAbits.TRISA3 // UART CTS_2 - Clear to Send - Input [CTS PI]
#define UART_TRIS_RTS_PI TRISAbits.TRISA2 // UART_RTS_2 - Ready to Send - Input [RTS PI]
#define SPI_TRIS_SCK TRISBbits.TRISB14 // SPI SCK - Serial Clock Pin (PPS?)
#define SPI_TRIS_SDO TRISBbits.TRISB6 // SPI SDO - Serial Data Out Pin (PPS?)
#define SPI_TRIS_CS_1 TRISBbits.TRISB8 // SPI CS1 - DAC 2 Chip Select Pin (PPS?)
#define SPI_TRIS_CS_2 TRISBbits.TRISB7 // SPI CS2 - DAC 1 Chip Select Pin (PPS?)
#define AN4_TRIS TRISBbits.TRISB2 // Analogue Read 3
#define AN3_TRIS TRISBbits.TRISB1 // Analogue Read 2
#define AN2_TRIS TRISBbits.TRISB0 // Analogue Read 1
#define V_REF_TRIS_Plus TRISAbits.TRISA0 // Analogue V_REF(+) (Forms VRange)
#define V_REF_TRIS_Minus TRISAbits.TRISA1 // Analogue V_REF(-) (Forms VRange)
#define Reg_Enable_TRIS_D TRISBbits.TRISB9 // Regulator Digital Control (Output)
#define Reg_Enable_TRIS_M TRISBbits.TRISB12 // Regulator Button (Input)
// Port Input/Output Configuration [TRISB]
TRISB = 0x1004; // All of PortB set as Outputs Except for RB12 (Reg Enable) and RB2 (Input -> Analogue Input (Voltage)) (Port B) = (0000 ... 0100)
TRISA = 0x0003; // Set up A0 [Pin 2] and A1 [Pin 3] as V_REF(+) and V_REF(-) Respectively (Port B) = (0000 ... 0011)
UART_TRIS_RX = 1; // UART Receiver ~ Input
UART_TRIS_TX = 0; // UART Transmission ~ Output
UART_TRIS_CTS_PIC = 0; // UART "CTS_PIC" ~ Output
UART_TRIS_RTS_PIC = 0; // UART "RTS_PIC" ~ Output
UART_TRIS_CTS_PI = 1; // UART "CTS_PI" ~ Input
UART_TRIS_RTS_PI = 1; // UART "RTS_PI" ~ Input
SPI_TRIS_SCK = 0; // SPI Clock ~ Output
SPI_TRIS_SDO = 0; // SPI Data Output ~ Output
SPI_TRIS_CS_1 = 0; // SPI Chip Select 1 ~ Output
SPI_TRIS_CS_2 = 0; // SPI Chip Select 2 ~ Output
AN4_TRIS = 1; // Analogue Read In ~ Input
AN3_TRIS = 1; // Analogue Read In ~ Input
AN2_TRIS = 1; // Analogue Read In ~ Input
V_REF_TRIS_Plus = 1; // V_Ref(+) ~ Input
V_REF_TRIS_Minus = 1; // V_Ref(-) Differential Measurements ~ Input
Reg_Enable_TRIS_D = 0; // Regulator Digital Control (Output)
Reg_Enable_TRIS_M = 1; // Regulator Switch Control (Input)
// Peripheral Pin Select Configurations
U1RXR = 0x0011; // UART PPS Mapping
RPB15R = 0x0001; // UART PPS Mapping
// Analogue Pin Configurations
ANSELB = 0x0028; // RB0 RB1 RB2 = AN2 AN3 AN4 [0001 1100]
ANSELA = 0x0000; // Set all Analogue Inputs of Port A Off
//**************Sub-System Configurations*********************************//
// UART Control Configure
UART_Config(); //UART Control Configure
#define PIC_CTS LATAbits.LATA4 // Output Set Definition [1]
#define PIC_RTS LATBbits.LATB4 // Output Set Definition [2]
#define PI_CTS PORTAbits.RA3 // Input Read Definition [2]
#define PI_RTS PORTAbits.RA2 // Input Read Definition [1]
// Analogue Control Configure
ADC_Config(); // Configure ADC
AD1CON1SET = 0x8000; // Enable ADC
//***************Variable Declarations************************************//
enum Comm_State Communication_State = Phase1A; //Controller Variable
unsigned int temp1 = 0;
unsigned int Comms_Flag_1 = 0;
unsigned int ConFlag = 1;
unsigned int i = 1;
unsigned int UART_ADC_CV_1 = 0;
unsigned int UART_ADC_CV_2 = 0;
unsigned int ADC_CV = 0;
unsigned int UART_ADC_CC_1 = 0;
unsigned int UART_ADC_CC_2 = 0;
unsigned int ADC_CC = 0;
unsigned int DAC_CV = 0;
float I_CC = 0;
float V_CV = 0;
//***************Program Flow - Switch State Controlled*******************//
while(1)
{
switch (Communication_State)
{
case Phase1A: // Check For Pi Ready to Send CV ADC Value
//PIC_CTS = 0;
//Pic_Refresh();
PIC_RTS = 0;
PIC_CTS = 1;
if (PI_RTS == 1)
{
PIC_CTS = 0;
Communication_State = Phase1B;
}
break;
case Phase1B: // Receive CV ~ 12 Bit ADC Value [Two Data Packets with 0.01 Second Delay]
ConFlag = 1;
i = 1;
while (ConFlag == 1)
{
if (PI_RTS == 1 && i == 1)
{
UART_ADC_CV_1 = Read_UART_Data(); //Data Packet 1 Returned - MSB(Bit 15) to Bit 8
i++;
}
else if (PI_RTS == 1 && i == 2)
{
UART_ADC_CV_2 = Read_UART_Data(); //Data Packet 2 Returned - Bit (7)) to LSB(Bit 0)
}
else
{
ConFlag = 0;
}
}
Communication_State = Phase1C;
break;
case Phase1C: // Check for CC Value
delay(); //Ensure that Pi_RTS has gone low after sending last Transmission (Prevents Code from Running Away)
PIC_CTS = 1;
if (PI_RTS == 1)
{
PIC_CTS = 0;
Communication_State = Phase1D;
}
break;
case Phase1D: // Receive CC Value [Two Data Packets with 0.01 Second Delay]
ConFlag = 1;
i = 1;
while (ConFlag == 1)
{
if (PI_RTS == 1 && i == 1)
{
UART_ADC_CC_1 = Read_UART_Data(); //Data Packet 1 Returned - MSB(Bit 15) to Bit 8
i++;
}
else if (PI_RTS == 1 && i == 2)
{
UART_ADC_CC_2 = Read_UART_Data(); //Data Packet 2 Returned - Bit (7)) to LSB(Bit 0)
}
else
{
ConFlag = 0;
}
}
Communication_State = Phase1E;
break;
case Phase1E: // Calculations
// CV Calculations
temp1 = UART_ADC_CV_1 << 8;
ADC_CV = temp1 + UART_ADC_CV_2;
V_CV = ADC_CV * (4.096/4096);
DAC_CV = ADC_CV | 4096;
Comms_Flag_1 = SPI_Transfer(DAC_CV ,1); // Data Transmitted to DAC 1, Upon Transmission LED Turns Green (No Acknowledgement)
// CC Calculations
temp1 = UART_ADC_CC_1 << 8;
ADC_CC = temp1 + UART_ADC_CC_2;
I_CC = ADC_CC * (4.096/4096);
Communication_State = Phase2A;
break;
case Phase2A:
while(1)
{
LATBbits.LATB5 = 1;
}
break;
}
}
return 1;
}

Answer 1

In Read_UART_Data, you have:
while(!U1STAbits.URXDA)
c = (int)U1RXREG;
I think you're missing a semicolon because this is actually:
while (!U1STAbits.URXDA)
c = (int) U1RXREG;
This means that c is set only when the UART receiver is not ready.
What I think you meant is:
while (!U1STAbits.URXDA);
c = (int) U1RXREG;