Question

我有一个关于从Raspberry Pi到mcp3008的数据传输的问题。这只是一个理论问题。当它们交换字节时，主机发送1个字节并接收1个字节。然后发送第二个字节并接收第二个字节..或者主机发送3个字节并在此之后接收3个字节。根据我的理解，这是第一个，我是对的吗？

Answer 1

Adafruit的MCP3008库有您的答案。查看read_adc()功能：

def read_adc(self, adc_number):
    """Read the current value of the specified ADC channel (0-7).  The values
    can range from 0 to 1023 (10-bits).
    """
    assert 0 <= adc_number <= 7, 'ADC number must be a value of 0-7!'
    # Build a single channel read command.
    # For example channel zero = 0b11000000
    command = 0b11 << 6                  # Start bit, single channel read
    command |= (adc_number & 0x07) << 3  # Channel number (in 3 bits)
    # Note the bottom 3 bits of command are 0, this is to account for the
    # extra clock to do the conversion, and the low null bit returned at
    # the start of the response.
    resp = self._spi.transfer([command, 0x0, 0x0])
    # Parse out the 10 bits of response data and return it.
    result = (resp[0] & 0x01) << 9
    result |= (resp[1] & 0xFF) << 1
    result |= (resp[2] & 0x80) >> 7
    return result & 0x3FF

它似乎发送一个三字节命令（其中只有一个字节非零）：

resp = self._spi.transfer([command, 0x0, 0x0])

响应是三个字节，包含打包的10位ADC值。

resp = self._spi.transfer([command, 0x0, 0x0])
# Parse out the 10 bits of response data and return it.
result = (resp[0] & 0x01) << 9
result |= (resp[1] & 0xFF) << 1
result |= (resp[2] & 0x80) >> 7

数据传输Pi / MCP3008

1 个答案: