hardwarespi.rst

cpp

HardwareSPI

This page describes how to use the built-in SPI ports. It does not describe the SPI protocol itself. For more information about SPI, see the SPI reference <spi>.

Contents

Getting Started

In order to get started, you'll first need to define a HardwareSPI variable, which you'll use to control the SPI port. Do this by putting the line "HardwareSPI spi(number);" with your variables, where number is the SPI port's number.

Here's an example (we'll fill in setup() <lang-setup> and loop() <lang-loop> later):

// Use SPI port number 1
HardwareSPI spi(1);

void setup() {
   // Your setup code
}

void loop() {
   // Do stuff with SPI
}

Turning the SPI Port On

Now it's time to turn your SPI port on. Do this with the begin() function (an example is given below).

HardwareSPI::begin

The speed at which the SPI port communicates is configured using a SPIFrequency value:

SPIFrequency

Note

Due to hardware issues, you can't use the frequency SPI_140_625KHz with SPI port 1.

You'll need to determine the correct values for frequency, bitOrder, and mode yourself, by consulting the datasheet for the device you're communicating with. Continuing our example from before, we'll add a call to begin() to our setup():

// Use SPI port number 1
HardwareSPI spi(1);

void setup() {
    // Turn on the SPI port
    spi.begin(SPI_18MHZ, MSBFIRST, 0);
}

void loop() {
   // Do stuff with SPI
}

If you call begin() with no arguments (as in "spi.begin();"), it's the same as if you wrote "spi.begin(SPI_1_125MHZ, MSBFIRST, 0);".

Communicating Over SPI

Now that you've got your SPI port set up, it's time to start communicating. You can send data using HardwareSPI::write(), receive data using HardwareSPI::read(), and do both using HardwareSPI::transfer().

Continuing our example from before, let's send a number over SPI and print out whatever we get back over lang-serialusb:

// Use SPI port number 1
HardwareSPI spi(1);

void setup() {
    // Turn on the SPI port
    spi.begin(SPI_18MHZ, MSBFIRST, 0);
}

void loop() {
   // Send 245 over SPI, and wait for a response.
   spi.write(245);
   byte response = spi.read();
   // Print out the response received.
   SerialUSB.print("response: ");
   SerialUSB.println(response, DEC);
}

HardwareSPI Class Reference

There are a number of other things you can accomplish with your spi object. A full function listing follows.

HardwareSPI

Deprecated Functions

The following functions are defined for now, but they have been deprecated, and will be removed in a future Maple IDE release. You shouldn't use them in new programs, and you should change any of your programs which do use them to the up-to-date functions discussed above.