Fingerprint Reader on Pic32mx

Question

I am struggling in trying to put a UART Port working (no flow control and no parity bit) in a PIC32MX in order to comunicate with a Fingerprint for too long, so I decided to get back to you guys. I just can put the fingerprint reader in digital I/O's because I have no more UART PORTs available. There's no problem for the TX pin but when it comes to enable RX pin (CN interrupt) I am seeing a problem.

This is the Fingerprint Reader I am using an this is the datasheet for the PIC.

I am using the CN4/RB2 Port for the Interrupt (Rx) and the RB0 to transmit. The compiler is XC32.

#include "NVMem.h"
#define Baudrate        4800   //bps
#define OneBitDelay     (1000000/Baudrate)  // microseconds
#define DataBitCount          8             // no parity, no flow control
#define UART_RX               TRISBbits.TRISB2  // UART RX pin
#define UART_TX               LATBbits.LATB0    // UART TX pin
#define UART_RX_DIR           TRISBbits.TRISB2 // UART RX pin direction
#define UART_TX_DIR           TRISBbits.TRISB0 // UART TX pin direction

int volatile readB = 0;
unsigned char UART_Receive(void);
void UART_Transmit(const char);

void __ISR(_CHANGE_NOTICE_VECTOR, ipl5) ChangeNoticeHandler(void)
{
readB = PORTB;      // Read PORTB to clear CN4 mismatch condition
if (readB){
    UART_Transmit(UART_Receive());
}

LATDINV = 0x0F;     // PORTG = 0xff;    // Toggle outputs.
IFS1CLR = 0x0001;   // Be sure to clear the CN interrupt status
}

unsigned char UART_Receive(void)
{
unsigned char DataValue = 0;
    unsigned char i = 0;

while(UART_RX==1);
delay_us(OneBitDelay);
delay_us(OneBitDelay/2); 
for (  i = 0; i < DataBitCount; i++ )
{
    if ( UART_RX == 1 )   //if received bit is high
    {
        DataValue += (1<<i);
    }
    delay_us(OneBitDelay);
}
if ( UART_RX == 1 )       //Stop bit should be high
{

        return DataValue;
}
else                      //some error occurred !
{
        delay_us(OneBitDelay);
        return 0x000;
}
}


void UART_Transmit(const char DataValue)
{
/* Basic Logic
   TX pin is usually high. A high to low bit is the starting bit and
   a low to high bit is the ending bit. No parity bit. No flow control.
   BitCount is the number of bits to transmit. Data is transmitted LSB     first.
*/
// Send Start Bit
UART_TX = 0;
delay_us(OneBitDelay);
unsigned char i;

for ( i = 0; i < DataBitCount; i++ )
{
    //Set Data pin according to the DataValue
    if( ((DataValue>>i)&0x1) == 0x1 )   //if Bit is high
    {
        UART_TX = 1;
    }
    else      //if Bit is low
    {
        UART_TX = 0;
    }
    delay_us(OneBitDelay);
}

//Send Stop Bit
UART_TX = 1;
}


void FingerprintRun(Task * task){
 CNCON = 0x8000;                 // Enable CN module

 CNEN = 0x00000010; // Enable individual CN pin CN4
 CNPUE = 0x00000010; // Enable weak pull up for pin CN4

 UART_TX = 1;           // TX pin is high in idle state
 UART_RX_DIR = 1;       // Input
 UART_TX_DIR = 0;       // Output

 readB = PORTB;

 IPC6SET = 0x00140000; // Set priority level=5
 IPC6SET = 0x00030000; // Set Subpriority level=3

 IEC1SET = 0x0001; // Enable Change Notice interrupts

UART_Transmit ('H');
UART_Transmit ('i');
UART_Transmit ('\r');

while(UART_RX==0){
    asm("nop");
}

while(1)
    {
    }
}

While debugging the Program Counter never goes to the interrupt.

Answer 1

your line: CNEN = 0x00000010; // Enable individual CN pin CN4

should be: CNEN = 0x00010000; // Enable individual CN pin CN4

and similar for CNPUE

You also need to implement timing in your software as per @brhans comments

Using delays in your interrupt routine is not be good practice - the CPU will not be able to do any other processing - including responding to other interrupts, in the time it takes to read each character, much better to start a timer and sample the port bit on that timers interrupt.