.. currentmodule:: pyb
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.
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
.. method:: SPI.deinit() Turn off the SPI bus.
.. method:: 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. - ``bits`` can be 8 or 16, and is the number of bits in each transferred word. - ``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 :meth:`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.
.. method:: 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``.
.. method:: 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``.
.. method:: 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.
.. data:: SPI.MASTER
.. data:: SPI.SLAVE for initialising the SPI bus to master or slave mode
.. data:: SPI.LSB
.. data:: SPI.MSB set the first bit to be the least or most significant bit