SoftSPI

This library contains a javascript class, which implements the SPI (Serial Peripheral Interface Bus) for a Raspberry Pi. In contrast to other libraries it is a software implementation. So it does not use the hardware SPI of the Raspberry Pi and you can choose any pin of the GPIO for the needed logic signals of SPI.

Motivation

I wanted to control some components with my Raspberry Pi, which are using SPI. But a couple of clients (e.g. WS2801 led stripe) do not support a client select. So I needed a software SPI and didn't find one for javascript. Now here is.

Precondition

The library is implemented in ECMAScript 2015, so your project should support at least this version.

Installation

Install it via npm:

$ npm install rpi-softspi

Usage

Start with importing the module via:

var SoftSPI = require("rpi-softspi")

Create an instance for your client device specifying the used pins and needed configurations for the communication in an options object:

let client = new SoftSPI({
   clock: 15,     // pin number of SCLK
   mosi: 11,      // pin number of MOSI
   miso: 13,      // pin number of MISO
   client: 16,    // pin number of CS
   clientSelect: rpio.LOW, // trigger signal for the client
   mode: 0,                // clock mode (0 - 3)
   bitOrder: SoftSPI.MSB   // bit order in communication
})

At least you have to specify the clock pin, all other can be left unspecified to use the default configuration

This is the default configuration:

default = {
   clock: null,
   miso: null,
   mosi: null,
   client: null,
   clientSelect: rpio.LOW,
   mode: 0,
   bitOrder: SoftSPI.MSB
}

Clock modes are:

| Mode | Polarity | Phase | | :---: | :---: | :---: | | 0 | 0 | 0 | | 1 | 0 | 1 | | 2 | 1 | 0 | | 3 | 1 | 1 |

Start the communication:

client.open()

The SoftSPI is in an invalid state till you open the communication. If it is invalid you cannot transfer data.

Close the communication:

client.close()

Once you close the communication the SoftSPI changes again to invalid state.

Read (only) a number of bytes from the client:

let bytes = client.read(5)
// bytes[0] = first byte

Write data (only) to the client:

client.write([0xff, 0x01, 0xab]) //supply any data

Transfer data to and from the client:

let bytes = client.transfer([0xff, 0x01, 0xab])

The number of returned bytes is the same number of bytes you have supplied

Example

We assume the connected client wants the numbers 1234 and continues to count by returning 5678.

var SoftSPI = require("rpi-softspi")

let client = new SoftSPI({
   clock: 15,     // pin number of SCLK
   mosi: 11,      // pin number of MOSI
   miso: 13,      // pin number of MISO
   client: 16,    // pin number of CS
})

client.open()
let send = [1, 2, 3, 4]
let answer = client.transfer(send)
// Count: 1,2,3,4...5,6,7,8
console.log("Count: " + send.toString() + "..." + answer.toString())
client.close()

API

Check out the documentation for details.

License

MIT

Additional Information

Find a description on Wikipedia - Serial Peripheral Interface Bus or with the keywords SPI as well as Serial Peripheral Interface.