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# 1.22 SERCOM SPI Client Read Write

This example application demonstrates how to use the SERCOM SPI peripheral in client mode.

## Description

This example uses the SERCOM SPI peripheral library in client mode and allows reading and writing data from/to its internal buffer by a SPI host.

The SPI host writes data by sending a write command followed by two bytes of memory address followed by the data to be written.

< WR_CMD > < ADDR_MSB > < ADDR_LSB > < DATA0 > … < DATA n >

The SPI client asserts the Busy line to indicate to the SPI host that it is busy. Once ready, the SPI client de-asserts the Busy line. Once the SPI client is ready, the SPI host reads the data by sending read command followed by two bytes of memory address and the number of bytes to read.

< RD_CMD > < ADDR_MSB > < ADDR_LSB > < NUM_BYTES >

The SPI client responds by sending the data at the requested memory address. The SPI host compares the sent data with the received data and repeats the test if it matches.

## Downloading and Building the Application

To clone or download this application from Github, go to the main page of this repository and then click Clone button to clone this repository or download as zip file. This content can also be downloaded using content manager by following these instructions.

Path of the application within the repository is apps/sercom/spi/slave/spi_write_read/firmware.

To build the application, refer to the following table and open the project using its IDE.

Project Name | Description
--- | ---
sam_d20_xpro.X | MPLABX project for SAM D20 Xplained Pro Evaluation Kit

## Setting Up the Hardware

The following table shows the target hardware for the application projects.

Project Name | Description
--- | ---
sam_d20_xpro.X | SAM D20 Xplained Pro Evaluation Kit

### Setting Up SAM D20 Xplained Pro Evaluation Kit

- To run this demo two SAM D20 Xplained Pro Evaluation Kit are required. One will be programmed as SPI host and other will be programmed as SPI client.
- Connect Pin 15, 16, 17, 18 on EXT2 of SPI client to Pin 15, 16, 17, 18 on EXT2 of SPI host
  - Pin 15 - SPI Chip Select
  - Pin 16 - MOSI
  - Pin 17 - MISO
  - Pin 18 - SCK
- Connect Pin 9 on EXT2 of SPI client to Pin 9 on EXT2 of SPI host. Pin 9 is configured as GPIO and serves as the client busy pin.
- Connect the Debug USB port on the board to the computer using a micro USB cable

## Running the Application

1. Build and Program the SPI host application project using its IDE. Path of the SPI Host application within the repository is apps/sercom/spi/master/spi_write_read_test_app/firmware
2. Build and Program the SPI client application project using its IDE.
3. On the SPI host board, press switch to start reading and writing data
4. LED on SPI host board indicates the success or failure:
   - LED is turned ON when the data read from the SPI client matches with the data written
   - LED is turned OFF when the data read from the SPI client does not match with the data written

Following table provides the Switch and LED name:

Board | Switch Name | LED Name
--- | --- | ---
SAM D20 Xplained Pro Evaluation Kit | SW0 | LED0