PythonExtra/docs/library/pyb.SPI.rst

class SPI -- a master-driven serial protocol

SPI is a serial protocol that is driven by a master. At the physical level there are 3 lines: SCK, MOSI, MISO.

port_pyboard

See usage model of I2C; SPI is very similar. Main difference is parameters to init the SPI bus:

from pyb import SPI
spi = SPI(1, SPI.MASTER, baudrate=600000, polarity=1, phase=0, crc=0x7)

Only required parameter is mode, SPI.MASTER or SPI.SLAVE. Polarity can be 0 or 1, and is the level the idle clock line sits at. Phase can be 0 or 1 to sample data on the first or second clock edge respectively. Crc can be None for no CRC, or a polynomial specifier.

Additional methods for SPI:

data = spi.send_recv(b'1234')        # send 4 bytes and receive 4 bytes
buf = bytearray(4)
spi.send_recv(b'1234', buf)          # send 4 bytes and receive 4 into buf
spi.send_recv(buf, buf)              # send/recv 4 bytes from/to buf

port_wipy

See usage model of I2C; SPI is very similar. Main difference is parameters to init the SPI bus:

from pyb import SPI
spi = SPI(1, SPI.MASTER, baudrate=1000000, polarity=0, phase=0, firstbit=SPI.MSB)

Only required parameter is mode, must be SPI.MASTER. Polarity can be 0 or 1, and is the level the idle clock line sits at. Phase can be 0 or 1 to sample data on the first or second clock edge respectively.

Constructors

port_pyboard

Construct an SPI object on the given bus. bus can be 1 or 2. 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 init for parameters of initialisation.

The physical pins of the SPI busses are:

• SPI(1) is on the X position: (NSS, SCK, MISO, MOSI) = (X5, X6, X7, X8) = (PA4, PA5, PA6, PA7)
• SPI(2) is on the Y position: (NSS, SCK, MISO, MOSI) = (Y5, Y6, Y7, Y8) = (PB12, PB13, PB14, PB15)

At the moment, the NSS pin is not used by the SPI driver and is free for other use.

port_wipy

Construct an SPI object on the given bus. bus can be only 1. 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 init for parameters of initialisation.

Methods

spi.deinit()

Turn off the SPI bus.

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spi.init(mode, baudrate=328125, *, prescaler, polarity=1, phase=0, bits=8, firstbit=SPI.MSB, ti=False, crc=None)

Initialise the SPI bus with the given parameters:

• mode must be either SPI.MASTER or SPI.SLAVE.
• baudrate is the SCK clock rate (only sensible for a master).
• prescaler is the prescaler to use to derive SCK from the APB bus frequency; use of prescaler overrides baudrate.
• polarity can be 0 or 1, and is the level the idle clock line sits at.
• phase can be 0 or 1 to sample data on the first or second clock edge respectively.
• firstbit can be SPI.MSB or SPI.LSB.
• crc can be None for no CRC, or a polynomial specifier.

Note that the SPI clock frequency will not always be the requested baudrate. The hardware only supports baudrates that are the APB bus frequency (see pyb.freq) divided by a prescaler, which can be 2, 4, 8, 16, 32, 64, 128 or 256. SPI(1) is on AHB2, and SPI(2) is on AHB1. For precise control over the SPI clock frequency, specify prescaler instead of baudrate.

Printing the SPI object will show you the computed baudrate and the chosen prescaler.

port_wipy

spi.init(mode, baudrate=1000000, *, polarity=0, phase=0, bits=8, firstbit=SPI.MSB, pins=(CLK, MOSI, MISO))

Initialise the SPI bus with the given parameters:

• mode must be SPI.MASTER.
• baudrate is the SCK clock rate.
• polarity can be 0 or 1, and is the level the idle clock line sits at.
• phase can be 0 or 1 to sample data on the first or second clock edge respectively.
• bits is the width of each transfer, accepted values are 8, 16 and 32.
• firstbit can be SPI.MSB only.
• pins is an optional tupple with the pins to assign to the SPI bus.

spi.write(buf)

Write the data contained in buf. Returns the number of bytes written.

spi.read(nbytes, *, write=0x00)

Read the nbytes while writing the data specified by write. Return the number of bytes read.

spi.readinto(buf, *, write=0x00)

Read into the buffer specified by buf while writing the data specified by write. Return the number of bytes read.

spi.write_readinto(write_buf, read_buf)

Write from write_buf and read into read_buf. Both buffers must have the same length. Returns the number of bytes written

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spi.recv(recv, *, timeout=5000)

Receive data on the bus:

• recv can be an integer, which is the number of bytes to receive, or a mutable buffer, which will be filled with received bytes.
• timeout is the timeout in milliseconds to wait for the receive.

Return value: if recv is an integer then a new buffer of the bytes received, otherwise the same buffer that was passed in to recv.

spi.send(send, *, timeout=5000)

Send data on the bus:

• send is the data to send (an integer to send, or a buffer object).
• timeout is the timeout in milliseconds to wait for the send.

Return value: None.

spi.send_recv(send, recv=None, *, timeout=5000)

Send and receive data on the bus at the same time:

• send is the data to send (an integer to send, or a buffer object).
• recv is a mutable buffer which will be filled with received bytes. It can be the same as send, or omitted. If omitted, a new buffer will be created.
• timeout is the timeout in milliseconds to wait for the receive.

Return value: the buffer with the received bytes.

Constants

port_pyboard

SPI.MASTER

SPI.SLAVE

for initialising the SPI bus to master or slave mode

SPI.LSB

SPI.MSB

set the first bit to be the least or most significant bit

port_wipy

SPI.MASTER

for initialising the SPI bus to master

SPI.MSB

set the first bit to be the most significant bit