I2C Repeated Start Conditions

[yiziliuxian]

I am trying use this library with some TI chip. Could you please explain how to use i2c.read(reg,length) to do Pointer Byte Set Followed by a Repeat Start and Word (Two Byte) Read as showing in the following figure? Now I can only use i2c.read and i2c.write seprately.

[i2cy]

A typical I2C read situation that resembles reading from mpu6050 chip:

The Pointer Byter from Master byte you mentioned resembles the Reg Address byte shown above, and they were both followed by a Repeat Start signal from the master device (CH347). And the whole process may break down to two seperated steps: write 1 byte and read couple of bytes (2 bytes in your specific situation).

To perform a Repeat Start and Word Read (that your document called Repeat Start and Word Read) using this libraray, the code may look like this:

from ch347api import I2CDevice as i2c

dev = i2c(addr=0x48)  # in case of A0=0, A1=0, replace with actual 7-bits address of yours
pointer = 0xff  # replace with your pointer byte
response = dev.read(reg=pointer, length=2)  # Repeat Start and Word Read

I hope this would help :)

[yiziliuxian]

I tired you code but I found it doesn't work. I am currently using the following code:

i2c = I2CDevice(addr=0x48, clock_freq_level=I2CClockFreq.f_100K)
i2c.write(reg=0x01)
d = i2c.read(reg=None, length=2)

It seems i2c.read only generates the pattern for addr + register_addr and read two bytes as shown in the following code. It is different from the pattern you showed: addr(write) +register_addr + addr(read) and read two bytes.

    def i2c_read(self, addr: (int, bytes), read_length: int,
                 register_addr: (int, bytes) = None) -> Tuple[bool, bytes]:
        """
        read byte(s) data from i2c bus with register address using 7-bits of device address
        :param addr: 7-bits of device address
        :type addr: :obj:`int`, :obj:`bytes`
        :param read_length: length of data to read from i2c bus
        :type read_length: int
        :param register_addr: Optional[int, bytes], one byte or several bytes of address of register,
        this method will automatically convert it into bytes with byte order 'big' unsigned if data type is int,
        e.g. 0x00f1f2 -> b'\xf1\xf2'
        :type register_addr: :obj:`int`, :obj:`bytes` (optional)
        :return: Tuple[operation_status bool, feedback bytes]
        :rtype: (bool, bytes)
        """
        # convert address
        if register_addr is None:
            register_addr = b""
            # convert address with reading signal
            addr = convert_i2c_address(addr, read=True)

        else:
            register_addr = convert_int_to_bytes(register_addr)
            # convert address with writing signal
            addr = convert_i2c_address(addr, read=False)

        # assemble payload
        payload = addr + register_addr

        # send and receive data from i2c bus
        status, feedback = self.__i2c_read_write_raw(payload, read_len=read_length)

I will show you the waveform I captured from the ouput of CH347 later.