# SPI¶

The spi module lets you talk to a device connected to your board using a serial peripheral interface (SPI) bus. SPI uses a so-called master-slave architecture with a single master. You will need to specify the connections for three signals:

• SCLK : Serial Clock (output from master).
• MOSI : Master Output, Slave Input (output from master).
• MISO : Master Input, Slave Output (output from slave).

## Functions¶

microbit.spi.init(baudrate=1000000, bits=8, mode=0, sclk=pin13, mosi=pin15, miso=pin14)

Initialize SPI communication with the specified parameters on the specified pins. Note that for correct communication, the parameters have to be the same on both communicating devices.

The baudrate defines the speed of communication.

The bits defines the size of bytes being transmitted. Currently only bits=8 is supported. However, this may change in the future.

The mode determines the combination of clock polarity and phase according to the following convention, with polarity as the high order bit and phase as the low order bit:

SPI Mode Polarity (CPOL) Phase (CPHA)
0 0 0
1 0 1
2 1 0
3 1 1

Polarity (aka CPOL) 0 means that the clock is at logic value 0 when idle and goes high (logic value 1) when active; polarity 1 means the clock is at logic value 1 when idle and goes low (logic value 0) when active. Phase (aka CPHA) 0 means that data is sampled on the leading edge of the clock, and 1 means on the trailing edge (viz. https://en.wikipedia.org/wiki/Signal_edge).

The sclk, mosi and miso arguments specify the pins to use for each type of signal.

spi.read(nbytes)

Read at most nbytes. Returns what was read.

spi.write(buffer)

Write the buffer of bytes to the bus.

spi.write_readinto(out, in)

Write the out buffer to the bus and read any response into the in buffer. The length of the buffers should be the same. The buffers can be the same object.