Class SPI – Serial Peripheral Interface Bus Protocol (Master)

What is SPI？

SPI is the abbreviation of Serial Peripheral Interface. It is a synchronous serial interface technology introduced by Motorola. It is a high-speed, full-duplex, synchronous communication bus. The SPI protocol is mainly used in short-distance communication systems, especially embedded systems. Many chip peripheral devices, such as LED display drivers, I / O interface chips, UART transceivers, etc., widely use the SPI bus protocol.

SPI is a synchronous serial protocol driven by the master device. 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 fourth signal SS (slave selection), used to select a specific device on the bus that communicates with. SS signal management should be carried out in user code（via:class:machine.Pin class）。

Construct object

class machine.SPI(id, ...)

Construct an SPI object on the given bus.

  • id - hardware SPI at 1，the default value is to build software SPI.

Construction of hardware SPI:

>>> 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)
>>>

软SPI的构建:

from machine import SPI, Pin

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

Method

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

Initialize SPI bus with given parameters：

  • baudrate SCK clock frequency。
  • polarity 0 or 1, the level of the idle clock line。
  • phase 0 or 1 to sample data on the first or second clock edge, respectively.
  • bits The width of each transmission (in bits). All hardware is guaranteed to support only 8。
  • firstbit can be SPI.MSB or SPI.LSB.
  • sck, mosi, miso is the pins (machine.Pin) object for bus signals. For most hardware SPI blocks (selected by the parameters of the id build object), the pins are fixed and cannot be changed. In some cases, the hardware module allows 2-3 alternative pin groups for the hardware SPI module. Any pin assignment only applies to bitbanging SPI driver（ id = -1）.
  • pins - esp32 do not have sck ， mosi ， miso parameters, but allows specifying them as a tuple pins .
SPI.deinit()

Turn off the SPI bus.

SPI.read(nbytes, write=0x00)

Read the specified number of bytes, nbytes and write a single byte continuously by the given write . Return objects containing bytes read data.

SPI.readinto(buf, write=0x00)

Read in 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 in `` buf`` .

Returns None。

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

SPI.write_readinto(write_buf, read_buf)

Write bytes from write_buf and read into read_buf . 缓冲区可以是相同的，也可以是不同的，但是两个缓冲区都必须具有 same length.

Returns None。

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

Constant

SPI.MASTER

Used to initialize the SPI bus to the host; this is only used for esp32.

SPI.MSB

Set the first digit to be the highest digit.

SPI.LSB

Set the first bit to the lowest bit.