SPI / Libraries / Processing.org

Class Name

SPI

Description

Opens an SPI interface as master

Serial Peripheral Interface (SPI) is a serial bus, commonly used to communicate with sensors and memory devices. It uses four pins: MOSI (Master Out Slave In), MISO (Master In Slave Out), and SCLK (clock signal) - those three are shared among all devices on the bus - as well as one or more SS (Slave Select) pins, that are used for the master to signal to the slave device that it is the desired respondent for the transmission.

The "master" device initiates a transfer by pulling the SS pin of the "slave" low, and begins outputting a clock signal. In SPI, both the "master" as well as the "slave" device output data at the same time. It is hence not possible to read data without writing some (even if it means outputting zeros or other dummy data).

There are multiple possible configuration settings for SPI, see settings() for details.

This library supports multiple SPI objects making use of the same SPI interface.

Examples

import processing.io.*;
SPI adc;

void setup() {
  //printArray(SPI.list());
  adc = new SPI(SPI.list()[0]);
  adc.settings(500000, SPI.MSBFIRST, SPI.MODE0);
}

void draw() {
  // read in values over SPI from an analog-to-digital
  // converter
  // dummy write, actual values don't matter
  byte[] out = { 0, 0 };
  byte[] in = adc.transfer(out);
  // some input bit shifting according to the datasheet
  int val = ((in[0] & 0x1f) << 5) | ((in[1] & 0xf8) >> 3);
  // val is between 0 and 1023
  println(val);
}

Constructors

SPI(dev)

Parameters

dev(String)device name

Methods

close()Closes the SPI interface
list()Lists all available SPI interfaces
settings()Configures the SPI interface
transfer()Transfers data over the SPI bus

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