SercomSPISlave

Introduction

This is a Sercom SPI library used for ATSAMD21 boards, such as the Arduino Zero and Adafruit Feather M0. It provides functions to setup SPI Slaves using Sercom1 and Sercom4.

To use it with the Arduino IDE, simply copy the the folder into the Arduino library folder.

Two examples are provided to set up a:

• Sercom1 SPI Slave
• Sercom4 SPI Slave

Why would I set up a board as an SPI slave?

Setting up a board as a SPI slave can be used to for instance communicate over SPI between a Raspberry Pi (SPI master) and an ATSAMD21 based board (SPI slave).

Hardware implementation

The pins used when the board is set up as an SPI Slave using Sercom1 are:

SPI pin	description	ATSAMD21 pin
MOSI	Master Out Slave In	PA16
SCK	Serial Clock	PA17
SS	Slave Select	PA18
MISO	Master In Slave Out	PA19

The pins used when the board is set up as an SPI Slave using Sercom4 are:

SPI pin	description	ATSAMD21 pin
MOSI	Master Out Slave In	PA12
SCK	Serial Clock	PB09
SS	Slave Select	PB10
MISO	Master In Slave Out	PB11

Example: Adafruit Feather M0

To setup a Sercom4 SPI slave on an Adafruit Feather M0, connect the pins as follows:

SPI pin	ATSAMD21 pin	Arduino pin	Sercom#/PAD[#]
MOSI	PA12	PIN22	Sercom4/PAD[0]
SCK	PB09	PIN16	Sercom4/PAD[1]
SS	PB10	PIN23	Sercom4/PAD[2]
MISO	PB11	PIN24	Sercom4/PAD[3]

The pinout of the Adafruit Feather M0 is found here.

Please note that on the Adafruit Feather M0 the pin descriptions on the board do not match how the pins are used when using Sercom4.

References

• The development of this code was made possible with the support I received on the Arduino Forum in the following topic. My username is Maverick123.

• The datasheet of the Atmel SAM D21G microcontroller is found here. See Table 6-1 "PORT Function Multiplexing" to find the pins you can use for Sercom0, Sercom1, Sercom2, Sercom3, Sercom4 and Sercom5.

• A detailed description how to use the table can be found here.