class SPI -- a Serial Peripheral Interface bus protocol (master)

SPI is a synchronous serial protocol driven by a master. At the physical level, the bus consists of 3 lines: SCK, MOSI, MISO. Multiple devices can share the same bus. Each device should have a separate SS (slave select) signal to select which device on the bus to communicate with. The SS signal is usually controlled by a GPIO pin, which should be managed by user code (via the machine.Pin class).

什么是SPI？

SPI是串行外设接口(Serial Peripheral Interface)的缩写。是 Motorola 公司推出的一 种同步串行接口技术，是一种高速的，全双工，同步的通信总线。 SPI协议主要用于短距离的通信系统中，特别是嵌入式系统，很多芯片的外围设备，比如LED显示驱动器、I／O接口芯片、UART收发器等都广泛的采用SPI总线协议。

Constructors

class machine.SPI(id, ...)

Construct an SPI object on the given bus.

  • id - when 1, it's hardware SPI. When omitted, it constructs a software SPI.

Hardware SPI construction:

>>> from machine import SPI
>>> hspi = SPI(1)
>>> hspi
SPI(id=1, baudrate=500000, polarity=0, phase=0, bits=8, firstbit=0, sck=-1, mosi=-1, miso=-1)
>>>

Software SPI construction:

from machine import SPI, Pin

spi = SPI(baudrate=100000, polarity=1, phase=0, sck=Pin(17), mosi=Pin(27), miso=Pin(18))

Methods

SPI.init(baudrate=1000000, *, polarity=0, phase=0, bits=8, firstbit=SPI.MSB, sck=None, mosi=None, miso=None, pins=(SCK, MOSI, MISO))

Initialise the SPI bus with the given parameters:

  • baudrate SCK clock frequency.

  • polarity 0 or 1, the level the clock is at when idle.

  • phase 0 or 1 to sample data on the first or second clock edge respectively.

  • bits width of each transfer, in bits. All hardware is guaranteed to support 8 bits.

  • firstbit can be SPI.MSB or SPI.LSB.

  • sck, mosi, miso are pins (machine.Pin) objects for the bus signals. For most hardware SPI blocks (selected by id parameter to the constructor), pins are fixed and cannot be changed. In some cases, hardware modules allow 2-3 alternative pin sets for a hardware SPI module. Arbitrary pin assignment is only possible for the bitbanging SPI driver (id = -1).

  • pins - esp32 does not have sck, mosi, miso parameters, but instead allows specifying them as a tuple via the pins parameter.

SPI.deinit()

Turn off the SPI bus.

SPI.read(nbytes, write=0x00)

Read the specified number of bytes, nbytes, while continuously writing the single byte given by write. Returns a bytes object containing the data read.

SPI.readinto(buf, write=0x00)

Read into the buffer specified by buf, while continuously writing the single byte given by write.

Returns None.

Note: On esp32, this function returns the number of bytes read.

SPI.write(buf)

Write the bytes contained in buf.

Returns None.

Note: On esp32, this function returns the number of bytes written.

SPI.write_readinto(write_buf, read_buf)

Write the bytes from write_buf while reading into read_buf. The buffers can be the same or different, but both buffers must have the same length.

Returns None.

Note: On esp32, this function returns the number of bytes written.

Constants

SPI.MASTER

Used to initialize the SPI bus as a master; this is only used on esp32.

SPI.MSB

Set the first bit to the most significant bit.

SPI.LSB

Set the first bit to the least significant bit.