Basic SPI not working pic16

[Lipton2]

Hey!

I am trying to make a simple SPI connection with between a TC77 digital tempereture sensor and my PIC6f690.I have read all the datahseets very carefully and connected everything ok, but it doesn't seem to work..

When i try to read from the TC77 i need two INT, because it send a 13 bit signal. So i read the SSPBUF registers twice and then shift the registers to form one int. To check if the value is good, i send the output through UART to my PC with the pickit2 application. But when i check the temperature I only get the weird value of 73..

Can you please help me to find the problem?

#include <htc.h>
#include <pic16f690.h>



    void initTMR0 (void);
    void initUARTsend (void);
    void initSPI (void);
 signed int  SPI_receive();
 
    void UART_send(signed int temp_out);

    void main()
    {
       initTMR0();  //TMR0 init
       initUARTsend();  //   UART init
       initSPI();
        signed int temp;
       temp=0;
       PORTC=0;     // PORTC reset


      while(1)
      {
       temp = SPI_receive();
        __delay_ms(100);

       UART_send(temp);
      }
    }


    void initTMR0(void)
    {
       OPTION_REGbits.PS0=1; //Prescaler is divide by 256
       OPTION_REGbits.PS1=1;
       OPTION_REGbits.PS2=1;
       OPTION_REGbits.PSA=0; //Timer Clock Source is from Prescaler
       OPTION_REGbits.T0CS=0;//Prescaler gets clock from FCPU (1MHz)

       INTCONbits.T0IE=1;   //Enable TIMER0 Interrupt
       INTCONbits.T0IF=0;
       INTCONbits.PEIE=1;     //Enable Peripheral Interrupt
       INTCONbits.GIE=1;      //Enable INTs globally
    }

    void initUARTsend(void)
    {
        SPBRG = 25; //Fosch 4Mhz -> baudrate 2400
        TXSTAbits.BRGH = 0;  //Sets Low Baud Rate
        TXSTAbits.SYNC = 0;  //Sets Asynchronous mode
        RCSTAbits.SPEN = 1;  //Enables EUSART
        TXSTAbits.TXEN = 1;  //Enables the EUSART transmiter
    }

    void initSPI(void)
    {
       TRISCbits.TRISC6=0;     //CS SPI output
       TRISCbits.TRISC7=0;      //SDO SPI out
       TRISBbits.TRISB6=0;      //SCK out
       TRISBbits.TRISB4=1;      //SDI SPI IN
        SSPCONbits.SSPEN = 1;   //= Enables serial port and configures SCK, SDO and SDI as serial port pins
        SSPCONbits.CKP = 1; //Idle state for clock is a low level (Microwire alternate)
        SSPCONbits.SSPM = 0;    //SPI Master mode, clock = FOSC/4
        SSPSTATbits.SMP = 0;    // Input data sampled at middle of data output time
        SSPSTATbits.CKE = 1;    //data transfer on rising edge clk

    }

   signed int SPI_receive()
   {

       signed int temp_out_msb;
       signed int temp_out_lsb;
       signed int temp_out;
       temp_out = 0;
       PORTCbits.RC6 = 0; //CS laag, initieer communicatie
       __delay_ms(10);
      SSPBUF = 0;  //dummy to start clk

        //First 8 bits
        while(!PIR1bits.SSPIF) //wait for receive complete
        temp_out_msb = SSPBUF;
        PIR1bits.SSPIF = 0;

        //last 6 bits
        SSPBUF = 0; // write dummy data again to initiate second receive
        while(!PIR1bits.SSPIF) //wait for receive complete
        temp_out_lsb = SSPBUF;
        PIR1bits.SSPIF = 0;

        PORTCbits.RC6 = 1; //CS high, stop SPI

        temp_out = ((temp_out_msb << 8 ) | (temp_out_lsb )); //shift bits to find temp

         return temp_out;

   }


   void UART_send(signed int temp_out)
    {
                while(!TRMT);
                TXREG = temp_out; //Transmit the binary number 1x per se

   }

 

[FvM]

SSPCONbits.CKP = 1; //Idle state for clock is a low level (Microwire alternate)

The PIC datasheet tells different.

 

[Lipton2]

Oh yeah that is a mistake in the comment section. Since the TC77 has only three SPI connections i am using the microwire default.

 

[spudboy488]

I can't remember where I read this but it is what I do and have not had problems. You should disable the SPI module (SSPEN=0), do all the SPI configuration (mode, speed, etc.), then enable the SPI module. The way your code is written (assuming I remembered correctly), the SPI module is using the power-up defaults and not what you are setting it to.

Also, use this chart to correctly set the mode. The mode should be listed in the data sheet for the peripheral.

/*	
  Standard SPI Mode | Microchip PIC
     Terminology    | Control Bits
   Using CPOL,CPHA  |   CKP CKE
 -------------------+--------------
       0,0 (0)      |    0   1
       0,1 (1)      |    0   0
       1,0 (2)      |    1   1
       1,1 (3)      |    1   0
*/

 

[Lipton2]

Hmm that sounds quite logical, but i tried it and it didn´t work for me

The datasheet of the TC77 states that "The microcontroller serial I/O bus master clocks
the data in on the rising edge of SCK. The falling edge
of SCK is then used to clock out the rest of the data."

When i compare that with the standard SPI terminology I selected CKP = 0 and CKE = 1, which leaves me with mode 0.
But still nothing.. Some other tips maybe?

My new code:

#include <htc.h>
#include <pic16f690.h>


    void initTMR0 (void);
    void initUARTsend (void);
    void initSPI (void);
    signed int  SPI_receive();
   // void SPI_send();
    void UART_send(signed int temp_out);

    void main()
    {

            ANSEL = 0;
    ANSELH = 0;
       initTMR0();  //TMR0 init
       initUARTsend();  //   UART init
       initSPI();
       signed int temp;
       temp=0;
      
      while(1)
      {
         temp = SPI_receive();
         __delay_ms(100);
         UART_send(temp);
      }
    }


    void initTMR0(void)
    {
       OPTION_REGbits.PS0=1; //Prescaler is divide by 256
       OPTION_REGbits.PS1=1;
       OPTION_REGbits.PS2=1;
       OPTION_REGbits.PSA=0; //Timer Clock Source is from Prescaler
       OPTION_REGbits.T0CS=0;//Prescaler gets clock from FCPU (1MHz)

       INTCONbits.T0IE=1;   //Enable TIMER0 Interrupt
       INTCONbits.T0IF=0;
       INTCONbits.PEIE=1;     //Enable Peripheral Interrupt
       INTCONbits.GIE=1;      //Enable INTs globally
    }

    void initUARTsend(void)
    {
        SPBRG = 25; //Fosch 4Mhz -> baudrate 2400
        TXSTAbits.BRGH = 0;  //Sets Low Baud Rate
        TXSTAbits.SYNC = 0;  //Sets Asynchronous mode
        RCSTAbits.SPEN = 1;  //Enables EUSART
        TXSTAbits.TXEN = 1;  //Enables the EUSART transmiter
    }

    void initSPI(void)
    {
       //SSPCONbits.SSPEN = 0;   //= Enables serial port and configures SCK, SDO and SDI as serial port pins
       TRISCbits.TRISC6=0;     //CS SPI output
       TRISCbits.TRISC7=0;      //SDO SPI out
       TRISBbits.TRISB6=0;      //SCK out
       TRISBbits.TRISB4=1;      //SDI SPI IN

       SSPSTATbits.CKE = 1;    //data transfer on rising edge clk
       SSPCONbits.SSPM = 0;    //SPI Master mode, clock = FOSC/4
       SSPSTATbits.SMP = 0;    // Input data sampled at middle of data output time
       SSPCONbits.CKP = 0; //Idle state for clock is a low level (Microwire alternate)
       SSPCONbits.SSPEN = 1;

    }

   signed int SPI_receive()
   {
      signed int temp_out_msb;
      signed int temp_out_lsb;
      signed int temp_out;
      temp_out = 0;
        
      PORTCbits.RC6 = 0; //CS laag, initieer communicatie
      __delay_ms(10);
      SSPBUF = 0;  //dummy to start clk

       //First 8 bits
      while(!PIR1bits.SSPIF) //SSPBUF full flag
      temp_out_msb = SSPBUF;
      PIR1bits.SSPIF = 0;

      //last 6 bits
      SSPBUF = 0;
      while(!PIR1bits.SSPIF)//SSPBUF full flag
      temp_out_lsb = SSPBUF;
      PIR1bits.SSPIF = 0;

      PORTCbits.RC6 = 1; //CS hoo, stop SPI

      temp_out = ((temp_out_msb << 8 ) | temp_out_lsb); //shift bits to find temp
      return temp_out;
   }



   void UART_send(signed int temp)
   {
        while(!TRMT);
        TXREG = temp; //Transmit the binary number 1x per se
   }

 

[spudboy488]

I could only suggest trying the other 3 modes. One thing you may want to try is to set temp_out to a known value at the end of the SPI_receive() function and debug your UART code. You are passing in a 16 bit value but only transmitting 8 bits of it.

 

[FvM]

Mode 0 is correct for TC77, there must be a different problem. Maybe it's your harware?