Problem with SPI and ADXL345

[FilipF303RE]

Hi, I’m having trouble reading measurements from the ADXL345 using SPI. I’ve attached a picture from the debugger that shows a view of the variables. The SPI is configured as master full duplex, and I’ve included a screenshot showing the SPI configuration. The SCK is connected to SCL, MISO to SDO, MOSI to SDA, and CS is connected to a configured output. I’m looking for help because I can’t figure out how to solve this issue.

int main(void)

{

void adxl_init(void);

while (1)

{

adxl_read(0x32);

// x = (data_rec[1]<<8|data_rec[0]);

// y = (data_rec[3]<<8|data_rec[2]);

// z = (data_rec[5]<<8|data_rec[4]);

x = ((data_rec[1] << 8) | data_rec[0]);

y = ((data_rec[3] << 8) | data_rec[2]);

z = ((data_rec[5] << 8) | data_rec[4]);

xg = x*.0078;

yg = x*.0078;

zg = x*.0078;

}

}

void adxl_write (uint8_t address, uint8_t value)

{

uint8_t data[2];

data[0] = address|0x40; // multibyte write

data[1] = value;

HAL_GPIO_WritePin (GPIOB, GPIO_PIN_6, GPIO_PIN_RESET); // pull the cs pin low

HAL_SPI_Transmit (&hspi2, data, 2, 100); // write data to register

HAL_GPIO_WritePin (GPIOB, GPIO_PIN_6, GPIO_PIN_SET); // pull the cs pin high

}

void adxl_read (uint8_t address)

{

address |= 0x80; // read operation

address |= 0x40; // multibyte read

HAL_GPIO_WritePin (GPIOB, GPIO_PIN_6, GPIO_PIN_RESET); // pull the pin low

HAL_SPI_Transmit (&hspi2, &address, 1, 100); // send address

HAL_SPI_Receive (&hspi2, data_rec, 8, 100); // receive 6 bytes data

HAL_GPIO_WritePin (GPIOB, GPIO_PIN_6, GPIO_PIN_SET); // pull the pin high

}

void adxl_init(void)

{

adxl_write (0x31, 0x01);

adxl_write (0x2d, 0x00);

adxl_write (0x2d, 0x08);

}

void tx_com(uint8_t *tx_buffer, uint16_t len)

{

HAL_UART_Transmit(&huart2, tx_buffer, len, 1000);

}

[Andrew Neil]

Show a schematic of your hardware.

Please see the Posting Tips for how to properly post source code:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

---

@FilipF303RE wrote:

I’m having trouble reading measurements from the ADXL345 using SPI

---

What "trouble", exactly?

Can you successfully read the Device ID register ?

Are you sure CPOL and CPHA are correct?

Have you used an oscilloscope or logic analyser to check what's actually happening on the wires?

[FilipF303RE]

https://www.analog.com/media/en/technical-documentation/data-sheets/adxl345.pdf 

As you can see in the attached debugger screenshot, the reading from the accelerometer — specifically, the X, Y, and Z position measurement from the data_rec buffer array — is incorrect. I don’t have an oscilloscope. I’ve shared images from the ADXL345 datasheet PDF; if you could kindly check whether it’s configured correctly, I’d appreciate it. I have attached the schematic of my microcontroller in a PDF, along with a screenshot. The connections are as follows: D13 to SCL, D12 to SDO, D11 to SDA, and D10 to CS.

[Andrew Neil]

Again, Can you successfully read the Device ID register ?

If you can't do that, then there's something fundamentally wrong with the comms - so no point worrying about X,Y,Z values!

[FilipF303RE]

I tried this code with breakpoints, but the debugger was not reading the ID variable. Do you have any suggestions on how I could do this?

void adxl_read ()

{

uint8_t address = 0x00;

address |= 0x80;

uint8_t id;

HAL_GPIO_WritePin (GPIOB, GPIO_PIN_6, GPIO_PIN_RESET); // pull the pin low

HAL_SPI_Transmit (&hspi2, &address, 1, 100); // send address

HAL_SPI_Receive (&hspi2, &id, 1, 100); // receive 6 bytes data

HAL_GPIO_WritePin (GPIOB, GPIO_PIN_6, GPIO_PIN_SET); // pull the pin high

}

[Andrew Neil]

Again, see the Posting Tips for how to properly post source code:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

---

@FilipF303RE wrote:

the debugger was not reading the ID variable.

---

What do you mean by that ?

[FilipF303RE]

I set breakpoints in the void adxl_read() function, from the start to the end of the transmission, in order to read the device ID. At the start of the transmission, the variable address is set to 0x80, but at the end, in the function HAL_SPI_Receive(&hspi2, &id, 1, 100), I read 0x00 from the ID variable. I also tried HAL_SPI_Receive(&hspi2, &address, 1, 100), and got the same result. I can’t manage to read the device ID, and I’m not sure if I’m doing it correctly. The ID address of the ADXL345 accelerometer should be E5. Is this a correct way to try to read the ID address?

[gbm]

Don't use Receive, use TransmitReceive. See this topic:

https://community.st.com/t5/stm32-mcus-products/regarding-function-calls-when-performing-spi-communication-in/m-p/738412#M265178

[Saket_Om]

Hello @FilipF303RE 

Did you check if the SPI timing fits the characteristics specified in Table 10 of the slave datasheet?

[FilipF303RE]

I tried to read the ID using TransmitReceive, but it didn’t work; after the transmission, it shows the address 0x00. Does this mean that I have incorrectly configured the SPI registers? It's strange because I configured them as described in the text documentation. So, the only possible troubleshooting method is using an oscilloscope?