BQ76952EVM: Communicating with BQ76952EVM 7695_0_36 over SPI

Edit: I forgot to mention that I am not using the onboard MCU to communicate with the BQ76952, but an external MCU (tm4c123 family).

Hi Kyle,

It might be easier to try these steps using the MCU on board first to verify. This will make sure the device really is transitioning to SPI mode successfully.

One thing I do not see in your steps is you should send the commands to enter CONFIG_UPDATE mode before writing the register and to exit this mode afterwards. The SPI protocol can also be a little tricky for this device. Make sure your code is following the recommendations in the TRM and the Software Development guide (https://www.ti.com/lit/an/sluaa11a/sluaa11a.pdf ). I can also send you an ARM example using SPI through a private message if you send me an E2E friend request.

Best regards,

Matt

Hi Matt,

I forgot to mention, but I do enter config update mode before writing to any RAM registers, and then exit right after.

I followed the Software Dev Guide and wrote some conservative code for checking the MISO line for a read back of the data I sent before moving on to the next byte, as shown below. 

int16_t BQ76952::GetCellVoltage(uint8_t cell_number)
{
    bool success = false;
    uint32_t tx_voltage_array[3];
    uint8_t rx_voltage_array[2];
    uint8_t cell = GetCellNumber(cell_number);
    int16_t voltage;

    for (uint8_t index = 0; index < 2; index++) //writing 2 bytes of data to one of these registers
    {
        tx_voltage_array[0] = cell;
        tx_voltage_array[1] = 0xFF; //not sending anything when reading voltages
        tx_voltage_array[2] = ComputeCRC8(tx_voltage_array, 2);

        while (!success)
        {
            spi->Transfer(tx_voltage_array, rx_data_array, 3);

            if (rx_data_array[0] == cell)
            {
                success = true;
                //TODO Add logic for checking CRC
                rx_voltage_array[index] = rx_data_array[1];
            }
        }

        success = false;
        cell++;
    }
    voltage = static_cast<int16_t>(rx_voltage_array[0] << 8
            | rx_voltage_array[1]);
    return voltage;
}

As you can see, I enter a while loop while waiting for the device to read back what I have sent, because usually the first bytes on the MISO line are 0xFFFFFF and then  0xFFFF00. This style is typical of my functions for sending direct commands, subcommands/data subcommands, and when writing to RAM registers. I also found example code for SPI and I2C on this forum and I see they do the same while loop checking process that I do.

The problem with using the onboard MCU is BQ studio doesn't recognize the 7695_0_36 device that I am using, and also doesn't give me one of the options necessary for configuring SPI(setting SPI communications register to 0x60). The only close option I can select is 7695_0_28.

Another problem with using the onboard MCU is that I have to change the jumpers back and forth from external I2C to Internal I2C to send my commands that change to SPI, and then BQ studio wont show anything when I'm not connected for internal MCU connection.

I really just need an example of how to set up the dev kit for external SPI use so I can see if I have a jumper or configuration missing. Thank you.

Sincerely,

Kyle Garland

Hi Kyle,

It looks like you need to update your version of BQStudio. You should download the BQSTUDIO-TEST version so that the latest devices are included. The reason I recommend connecting with BQStudio first is to confirm the device is functioning properly apart from your code.

Regards,

Matt

Hi Matt,

That sounds good to me, I'll install the newest test version of BQStudio and check to see if I can connect to SPI and get back to you later today. 

Also, would I need to change the jumpers for internal SPI usage after switching from I2C to SPI mode, and then remove those jumpers and connect my external SPI wires to test my code when I know the device is in SPI mode? 

-Kyle

Yes, jumpers installed for internal SPI usage and removed when you connect the external SPI.