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SPI between MSP430/432 and MCP3911 always got 0'S or 1's

Discussion in 'Microcontrollers, Programming and IoT' started by Sunnyback, Apr 27, 2018.

  1. Sunnyback


    Apr 27, 2018

    I am trying to read ADC channel values from MCP3911 using MSP launchpad using SPI protocol. When i used Arduino Mega the protocol is working fine. But when i use any TI devices i am having a problem, it always gives me all 0'S or 1's.

    I am using energia for MSP devices. Any i have chosen the appropriate pins as defined in the enegia pin layout.


    static const uint8_t SS = 8; /* P2.7 */

    static const uint8_t SCK = 7; /* P3.2 */

    static const uint8_t MOSI = 15; /* P3.0 */

    static const uint8_t MISO = 14; /* P3.1 */

    Can someone help me troubleshoot where i am going wrong?

    // SPI Stuff here
    #include "SPI.h"
    const uint8_t MCP3911_CS = SS; // Teensy SPI CS1 = MCP3911
    void setup() {
      //SPI Bus setup
      digitalWrite(MCP3911_CS,HIGH); //
      pinMode (MCP3911_CS, OUTPUT); // MCP3911
      SPI.setClockDivider(SPI_CLOCK_DIV8); //i.e. 6MHz on a Teensy running at 48MHz.
      //Setup Serial Comms
      Write_MCP3911_Register (0x0D, B11000010);
    int32_t adc;
    void loop()
      //adc = Read_MCP3911_24bit(0x00);
    //  Serial.print("Ch0 :  ");
    //  Serial.println(adc);
    uint8_t Write_MCP3911_Register (uint8_t MCP3911_Register_Address, uint8_t Command) {
      Serial.print("Command Register Received: ");
      Serial.print(" - Command Received: ");
      MCP3911_Register_Address <<= 1;   //left shift address one digit
      MCP3911_Register_Address &= B00111110; // and ensure last digit is a zero for write command
      digitalWrite(MCP3911_CS, LOW); // now take CS low to enable SPI device
      SPI.transfer(MCP3911_Register_Address); // send address with write command to MCP3911
      SPI.transfer(Command); //now send payload
      digitalWrite(MCP3911_CS, HIGH); // deselect the CS pin.
      Serial.print(" Write Command Byte Sent: ");
      Serial.println(MCP3911_Register_Address,BIN); // verify what command was sent (i.e. address and write bit = 0)
      //Now Verify all went well. If so, have the function return value of one,
      //otherwise, alert the user that something is amiss.
      uint8_t Response = Read_MCP3911_Register (MCP3911_Register_Address>>1);
      if (Response == Command)  return 1;
        Serial.print("Error for register: ");
        Serial.print(" - Command Sent: ");
        Serial.print(" - Response Received: ");
        return 0;
    uint8_t Read_MCP3911_Register (uint8_t MCP3911_Register_Address) {
      MCP3911_Register_Address <<=1; //left shift address one bit for command byte
      MCP3911_Register_Address |=1; // Ensure read bit is set
      Serial.print("  Read Byte Command Sent: ");
      digitalWrite(MCP3911_CS, LOW);
      SPI.transfer(MCP3911_Register_Address); // send address with read command to MCP3911
      uint8_t Response = SPI.transfer(0x00);
      digitalWrite(MCP3911_CS, HIGH);
      Serial.print(" - Response Received: ");
      return Response;
    void Reset_ADC()
     // Puts ADC into Reset Mode, i.e. stops ADC conversions until setup is complete.
      Write_MCP3911_Register (0x0D, B11000010);
    int32_t Read_MCP3911_24bit( uint8_t MCP3911_Register_Address)
        uint8_t HB,MB,LB=0, MCP3911_CTRL=0;;
        int32_t adc0code=0;
        MCP3911_CTRL = 0;
        MCP3911_CTRL =(MCP3911_Register_Address<<1); //left shift address one digit for write command
        MCP3911_CTRL |= 1; //Turn on Read Operation by toggling last bit on
        digitalWrite(MCP3911_CS, LOW);
        SPI.transfer(MCP3911_CTRL); // send command byte to MCP3911
        HB = SPI.transfer(0x0);//receive High Byte
        MB = SPI.transfer(0x0);//receive Middle Byte
        LB = SPI.transfer(0x0);//receive Low Byte
        digitalWrite(MCP3911_CS, HIGH);
        adc0code = HB;
        adc0code = adc0code<<8;
        adc0code |= MB;
        adc0code = adc0code<<8;
        adc0code |= LB;         //connecting the 3 bytes to one number
        return adc0code;// returning result
    Will there be anyother connections running between MSP and MCP other than SS, SCK, MOSI, MISO?
    Where to connect GND? and is it required for the SPI?

    Oscilloscope shows the MOSI line from MSP is outputting data as expected. Also will pullup, pulldown states of pins matter?

    If u have a moment, it would be great if you can try the code I posted above and see if ur having any issues on your setup.

    Buy the way, I am using MSP430FF5529 launchpad, energia 17..

    Thanks in advance.
  2. kellys_eye


    Jun 25, 2010
    A common ground between the devices is required.

    Have you checked for logic level compatibility?
  3. Sunnyback


    Apr 27, 2018
    Hi kellys_eye, thanks for your reply.
    Sorry for my late response, i don't think it is the logic level causes trouble, in fact there is another micro controller on the board that is connected to the MCP3911 (only hoping using this to develop the model), so i am thinking if it will fight the MSP430 for control over SPI and lead to unexpected results...We'll get rid of it and develop our on Analog front end. Will check and see if i can read the values now. Will post if i see any trouble doing so. I just read the control register and its outputting the setting i write.
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