class SPI – a Serial Peripheral Interface bus protocol (controller side)¶
SPI is a synchronous serial protocol that is driven by a controller. At the physical level, a bus consists of 3 lines: SCK, MOSI, MISO. Multiple devices can share the same bus. Each device should have a separate, 4th signal, CS (Chip Select), to select a particular device on a bus with which communication takes place. Management of a CS signal should happen in user code (via machine.Pin class).
Both hardware and software SPI implementations exist via the
machine.SoftSPI classes. Hardware SPI uses underlying
hardware support of the system to perform the reads/writes and is usually
efficient and fast but may have restrictions on which pins can be used.
Software SPI is implemented by bit-banging and can be used on any pin but
is not as efficient. These classes have the same methods available and
differ primarily in the way they are constructed.
from machine import SPI, Pin spi = SPI(0, baudrate=400000) # Create SPI peripheral 0 at frequency of 400kHz. # Depending on the use case, extra parameters may be required # to select the bus characteristics and/or pins to use. cs = Pin(4, mode=Pin.OUT, value=1) # Create chip-select on pin 4. try: cs(0) # Select peripheral. spi.write(b"12345678") # Write 8 bytes, and don't care about received data. finally: cs(1) # Deselect peripheral. try: cs(0) # Select peripheral. rxdata = spi.read(8, 0x42) # Read 8 bytes while writing 0x42 for each byte. finally: cs(1) # Deselect peripheral. rxdata = bytearray(8) try: cs(0) # Select peripheral. spi.readinto(rxdata, 0x42) # Read 8 bytes inplace while writing 0x42 for each byte. finally: cs(1) # Deselect peripheral. txdata = b"12345678" rxdata = bytearray(len(txdata)) try: cs(0) # Select peripheral. spi.write_readinto(txdata, rxdata) # Simultaneously write and read bytes. finally: cs(1) # Deselect peripheral.
- class machine.SPI(id, ...)¶
Construct an SPI object on the given bus, id. Values of id depend on a particular port and its hardware. Values 0, 1, etc. are commonly used to select hardware SPI block #0, #1, etc.
With no additional parameters, the SPI object is created but not initialised (it has the settings from the last initialisation of the bus, if any). If extra arguments are given, the bus is initialised. See
initfor parameters of initialisation.
- class machine.SoftSPI(baudrate=500000, *, polarity=0, phase=0, bits=8, firstbit=MSB, sck=None, mosi=None, miso=None)¶
Construct a new software SPI object. Additional parameters must be given, usually at least sck, mosi and miso, and these are used to initialise the bus. See
SPI.initfor a description of the parameters.
- 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:
baudrateis the SCK clock rate.
polaritycan be 0 or 1, and is the level the idle clock line sits at.
phasecan be 0 or 1 to sample data on the first or second clock edge respectively.
bitsis the width in bits of each transfer. Only 8 is guaranteed to be supported by all hardware.
misoare pins (machine.Pin) objects to use for bus signals. For most hardware SPI blocks (as selected by
idparameter to the constructor), pins are fixed and cannot be changed. In some cases, hardware blocks allow 2-3 alternative pin sets for a hardware SPI block. Arbitrary pin assignments are possible only for a bitbanging SPI driver (
pins- WiPy port doesn’t
misoarguments, and instead allows to specify them as a tuple of
In the case of hardware SPI the actual clock frequency may be lower than the requested baudrate. This is dependant on the platform hardware. The actual rate may be determined by printing the SPI object.
Turn off the SPI bus.
- SPI.read(nbytes, write=0x00)¶
Read a number of bytes specified by
nbyteswhile continuously writing the single byte given by
write. Returns a
bytesobject with the data that was read.
- SPI.readinto(buf, write=0x00)¶
Read into the buffer specified by
bufwhile continuously writing the single byte given by
Write the bytes contained in
- SPI.write_readinto(write_buf, read_buf)¶
Write the bytes from
write_bufwhile reading into
read_buf. The buffers can be the same or different, but both buffers must have the same length. Returns
for initialising the SPI bus to controller; this is only used for the WiPy