SPI communication with ADIS gyro

[dsPIC]

Hi I am trying to read the gyro rate out from one of these: http://www.analog.com/static/imported-f ... _16265.pdf
But my code is not working - it just ouputs 4626. I am using a dsPIC30F4011 with a 20Mhz crystal.

It uses 16-bit SPI and the address that I need to send to get the rotation rate is 0x0400. It will then send me back the rotation rate in a 14-bit number. I am using code that Sobrietytest posted which I slightly modifided for my part. I know that the gyro works because I have tested it on its evaluation board.

Here is the connection diagram:


Currently my code outputs the int 4626 constantly over the serial port and the number doesnt change. The number should be changing with the rotation rate.
Here is my code:

Code: Select all

#include <Spi_Const.h>

const char CS_PIN = 0;                    // CS pin is RF0
int HiByte;
int LoByte;
int XGValue;
short buffer;
char txt[6];
int i = 0;


void InitMain() {
  ADPCFG = 0xFFFF;                        // Set AN pins as digital

  // Initialise SPI module
  Spi_Init_Advanced(_SPI_MASTER, _SPI_16_BIT, _SPI_PRESCALE_SEC_5,
  _SPI_PRESCALE_PRI_4, _SPI_SS_DISABLE, _SPI_DATA_SAMPLE_END,
  _SPI_CLK_IDLE_HIGH, _SPI_ACTIVE_2_IDLE);

  TRISF.CS_PIN = 0;                       // Set CS pin as output
  PORTF.CS_PIN = 1;                       // Set CS high

  Uart2_Init(9600);                        // Initialise UART module

}


void readADIS() {

  PORTF.CS_PIN = 0;                       // Select DAC module
  Spi_Write(0x04);                        // Send data via SPI
  Spi_Write(0x00);                        // Send data via SPI
  PORTF.CS_PIN = 1;                       // Deselect DAC module
  
  Delay_us(15);                           // Stall period between data
  
  PORTF.CS_PIN = 0;                       // Select DAC module
  HiByte = Spi_Read(buffer);              // Read the MSByte
  LoByte = Spi_Read(buffer);              // Read the LSByte
  PORTF.CS_PIN = 1;                       // Deselect DAC module
  
  HiByte = (HiByte <<8);                  // Bitshift the MSByte 8 places left
  XGValue = HiByte + LoByte;              //then add them together
  XGValue = (XGValue & 0b0011111111111111); //Strip off the ND and EA flags

}


void main() {
  InitMain();

  while (1) {                             // Main loop
    readADIS();
    
    WordToStr(XGValue, txt);              // Convert XGValue to array of numbers
    for (i=0; i<6; i++)                   // Display XGValue on serial
    Uart2_Write_Char(txt[i]);
    Uart2_Write_Char('\n');               // new line

    Delay_ms(300);                        // Update rate

  }
}

Can anyone see why the code is not working?

Thanks

[Sobrietytest]

The most obvious error that I can see here is your implementation of 16-bit SPI, in this case TWO bytes are sent and received, Therefore your address send and data read can be done in one pass...

Code: Select all

void readADIS() { 

  PORTF.CS_PIN = 0;                       // Select DAC module 
  Spi_Write(0x0400);                       // SEND 2 BYTE ADDRESS
  //Spi_Write(0x00);                        // YOU DON'T NEED THIS
  PORTF.CS_PIN = 1;                       // Deselect DAC module 
  
  Delay_us(15);                           // Stall period between data 
  
  PORTF.CS_PIN = 0;                       // Select DAC module 
  XGValue = Spi_Read(buffer);          // READ 16-BIT DATA
  //LoByte = Spi_Read(buffer);          // YOU DON'T NEED THIS
  PORTF.CS_PIN = 1;                       // Deselect DAC module 
  
  //HiByte = (HiByte <<8);                  // YOU DON'T NEED THIS 
  //XGValue = HiByte + LoByte;           //YOU DON'T NEED THIS
  XGValue = (XGValue & 0b0011111111111111); //Strip off the ND and EA flags 

} 


void main() { 
  InitMain(); 

  while (1) {                             // Main loop 
    readADIS(); 
    
    WordToStr(XGValue, txt);              // Convert XGValue to array of numbers 
    for (i=0; i<6; i++)                   // Display XGValue on serial 
    Uart2_Write_Char(txt[i]); 
    Uart2_Write_Char('\n');               // new line 

    Delay_ms(300);                        // Update rate 

  } 
}

I haven't tested it but try it and see what happens.

[dsPIC]

Hi, This fixed it!
I changed _SPI_16_BIT to _SPI_8_BIT and _SPI_DATA_SAMPLE_MIDDLE and leaved the code the same and it now works. I will modify the code the way you have for neatness.

Code: Select all

  // Initialise SPI module
  Spi_Init_Advanced(_SPI_MASTER, _SPI_8_BIT, _SPI_PRESCALE_SEC_1,
  _SPI_PRESCALE_PRI_16, _SPI_SS_DISABLE, _SPI_DATA_SAMPLE_MIDDLE,
  _SPI_CLK_IDLE_HIGH, _SPI_ACTIVE_2_IDLE);

Thankyou very much.

[Sobrietytest]

NFP, get to it! I'm sorry if the 8-bit solution caused confusion. Good luck with your project.

[Mince-n-Tatties]

Hi, This fixed it!
I changed _SPI_16_BIT to _SPI_8_BIT and _SPI_DATA_SAMPLE_MIDDLE and leaved the code the same and it now works. I will modify the code the way you have for neatness.

Code: Select all

  // Initialise SPI module
  Spi_Init_Advanced(_SPI_MASTER, _SPI_8_BIT, _SPI_PRESCALE_SEC_1,
  _SPI_PRESCALE_PRI_16, _SPI_SS_DISABLE, _SPI_DATA_SAMPLE_MIDDLE,
  _SPI_CLK_IDLE_HIGH, _SPI_ACTIVE_2_IDLE);

changed _SPI_16_BIT to _SPI_8_BIT

if you look at what ST was adding a few answers above, it was to say that you have a PIC which has a 16 bit SPI module and you have a 16 bit SPI gyro, so instead of using the 2 x 8 bit software method (which is typically how we get around using 8 bit SPI pics while connectd to > 8 bit external devices) you should stick with working in 16 bit as supported by both devices.

its also likely that changed _SPI_DATA_SAMPLE_MIDDLE is a better timing fit for your device, so stick with that change unless you have a scope to confirm timings.

working in 16 bit will reduce code greatly in this case. and remove the need for external "built-in" functions

[dsPIC]

Yes, I'll perform some code compacting like you say.
Cheers