jInvent iolinker library
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Web: http://jinvent.de/iolinker

The iolinker Chips

Every iolinker chip functions as a dynamically configurable IO matrix. Its main functionality, besides IO extension, is to dynamically set up a matrix of GPIO connections, that allow direct pass-through of high-frequency signals. Circuits can thereby be configured and programmed on the fly. There are UART / SPI / I2C versions that allow for easy integration of up to 127 chips connected in parallel. PWM signal output is possible as well.

You can find the datasheet at http://jinvent.de/resources/iolinker_datasheet.pdf.

The iolinker Library

The iolinker library allows easy interfacing of the iolinker chips, on a PC, a Raspberry Pi or on an Arduino. It works with UART, SPI and I2C chips.


To use the library on a PC, simply switch into the iolinker library directory and use make clean test to compile and run the unit tests, or make clean pcserial to compile the serial test program.

To use the library on an Arduino, download the IOLinker.zip file, and use Sketch -> Import Library -> Add Library. Then paste below code examples into your main program.

To compile it on a Raspberry Pi, please install the WiringPi library first (http://wiringpi.com/download-and-install/). Also run sudo apt-get install g++-4.8. make -f Makefile.pi clean pi in the iolinker library directory is enough to compile a test program afterwards. Run it with sudo ./iolinker_pi.

Example usage

Note that wherever the examples use Serial.println(), the code may seem Arduino specific. But you could as well change the appropriate lines into a printf() statement for Raspberry or PC usage. The iolinker specific code is universal.

Initialization on PC and Raspberry

First include the library header and create a class object:

#include <IOLinker.h>

IOLinker iolinker;

Setting up the serial interface on a Raspberry or PC, to communicate with an UART iolinker chip:

iolinker.beginSerial("/dev/ttyAMA0"); // or ttyUSB0 or the like

Setting up the SPI interface on a Raspberry, to communicate with an SPI iolinker chip:

iolinker.beginSPI(0); // Channel 0

Setting up the I2C interface, for I2C chips:


Please make sure to run the wiringPi setup functions, e.g. wiringPiSetup(), before you use the iolinker library on the Raspberry.

Initialization on an Arduino:

Setting up the serial interface to communicate with UART iolinker chips:

Serial.begin(IOLINKER_BAUDRATE); // Use Serial1 on Arduino Leonardo!
while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only

Setting up the SPI interface, for SPI chips:


Setting up the I2C interface, for I2C chips:


Slave address set-up

You can connect up to 127 chips in parallel. Their addresses are set through their hardware slave address port (IN1 to IN7).

When using multiple, address collision obviously has to be avoided. I suggest you start with address 1 and go up from there.


When using only one chip, you can cheat if you aren't sure about its slave address:

/* Walk through possible slave addresses and use first one that works */
Serial.print("The first slave address is ");
Serial.println(iolinker.firstAddress(), DEC);

TYP: Changing pin types

By default, all pins on the iolinker chip are Tristate (open collector) inputs. Change those easily:

iolinker.setPinType(IOLinker::IOLINKER_OUTPUT, 1); // P1 is an output
iolinker.setPinType(IOLinker::IOLINKER_OUTPUT, 2); // P2 is an output
iolinker.setPinType(IOLinker::IOLINKER_INPUT, 2); // P2 is a tristate input now
iolinker.setPinType(IOLinker::IOLINKER_OUTPUT, 6, 64); // P6 to P64 are outputs

Outputs are low, until their output value is changed with the SET command.

SET: Change pin output value

// Don't forget to set pin types first, see TYP section.

iolinker.setOutput(true, 1); // P1 is high
iolinker.setOutput(false, 2); // P2 is low
iolinker.setOutput(true, 6, 48); // P6 to P48 are high

uint8_t s[] = { 0x00, 0xff };
iolinker.setOutput(s, sizeof(s), 49, 64); // P49 to P56 are low, P57 to P64 are high

REA: Read pin states

The readInput() method allows to determine pin states. On an Arduino this would work:

// Don't forget to set pin types first, see TYP section.

if (iolinker.readInput(3)) {
    Serial.println("P3 is high!");
} else {
    Serial.println("P3 is low!");

LNK: Link pins

Link two pins, and configure your circuit dynamically! The pin link allows to transfer MHz signals from one iolinker pin to another.

// Don't forget to set pin types first, see TYP section.

iolinker.link(3, 1); // P1 outputs all values from P3
iolinker.link(iolinker.invert(3), 2); // P2 outputs all values from
                                      // P3's inverted pin state
iolinker.link(3, 9, 11); // P9 to 11 output all values from P3
iolinker.link(IOLinker::IOLINKER_VIRTUAL_CLK256, 12); // P12 outputs the internal iolinker clock divided by 256

For more virtual pins, check out the iolinker datasheet, section "Pin addresses".

PWM: Activate pulse width modulation

// Don't forget to set pin types first, see TYP section.

iolinker.pwm(127, 6); // P6 is 100% on -- equals normal high state
iolinker.pwm(0, 7); // P7 is 0% on
iolinker.pwm(64, 8, 15); // P8 to P15 are ~50.4% on

iolinker.setOutput(true, 6, 15); // PWM output is only active when the pins are set to output type, and their output state is set to high

iolinker.setOutput(false, 12); // Turn PWM output on P12 back off, just for demonstration

Synchronizing pin updates

If you are updating a lot of pins individually and want the effect to be simultaneous, the iolinker chips allow to buffer pin settings. For that purpose, you first use the SYN command with iolinker.beginBuffering(), then run your pin update commands, and then trigger the simultaneous pin update using the TRG command with iolinker.executeBuffer().

// Prepare buffered pin update

// Your commands
iolinker.pwm(13, 8); // P8 will be ~10.23% on
iolinker.setOutput(true, 9); // P9 will be high
iolinker.setOutput(false, 10); // P10 will be low

/* Note that the last four commands did not have any effect on the
   actual pin states yet! We activate them all at once now: */

iolinker.executeBuffer(); // Simultaneous pin update!

CLR: Clear PWM output and link settings for pins

If you want to turn pin links back off for a pin and reuse it for something else, use the iolinker.clearPinFunctions(firstpin, lastpin) method.

iolinker.clearPinFunctions(1); // Reset settings for P1
iolinker.clearPinFunctions(2, 10); // Reset settings for P2 to P10

Listen for IO interrupts

The iolinker.registerInterrupt(pin) method on Arduino activates the pin change interrupt for the given pin number. The pin number is that on which you connected the INT line from the iolinker chip.

The iolinker.registerInterrupt(pin, callback_function) method on Raspberry activates the pin change interrupt and calls the function pointer provided on pin change. The callback function takes no parameters and returns void.

The simplest way to listen for interrupts on the iolinker input pins on an Arduino goes like this:

void setup() {
    // ...

    // INT pin connected to Arduino pin 9

ISR (PCINT0_vect) {
    Serial.println("One of the input pins just switched!");

A more elaborate approach with some debouncing would use the interrupt only to record events, and let the main program handle them periodically, such as this Arduino code:

#include <IOLinker.h>

IOLinker iolinker;
volatile uint8_t interrupt_event = 0;

ISR (PCINT0_vect) {
    interrupt_event = 1;

void setup() {
    while (!Serial) {
        ; // wait for serial port to connect. Needed for Leonardo only
    iolinker.beginSPI(); // Connect to SPI chip
    iolinker.targetAddress(1); // Address 1
    iolinker.setPinType(IOLinker::IOLINKER_INPUT, 3); // P3 is our input
    iolinker.registerInterrupt(9); // INT is connected to Arduino pin 9

    Serial.println("Now listening for pin interrupts on P3!");

void loop() {
    if (interrupt_event != 0) {
        Serial.println("New interrupt event!");
        Serial.print("My favorite pin is ");
        if (iolinker.readInput(3)) {
        } else {

        delay(300); // debounce button by ignoring events for 300ms
        interrupt_event = 0;

Reset chip state


Storing long command sequences in string buffer

If you want to save long command sequences more efficiently, e.g. to read a configuration from flash on boot, and to then write it out, the sendBuf(buf, len) method may be of use to you. The passed byte string contains only command bytes and arguments. The method takes care of adding target address and CRC and writes out the messages in the string one by one.

uint8_t iolinker_config[] = {
    0x82, 0x00, 0x01, 0x00, 0x0f, 0x03, /* TYP P1 to P15 as output */
    0x82, 0x00, 0x10, 0x00, 0x1f, 0x00, /* TYP P16 to P33 as input */
    0x83, 0x00, 0x01, 0x00, 0x07, 0x7f, /* SET P1 to P7 high */
    0x84, 0x00, 0x1f, 0x00, 0x00, 0x00, 0x0f, /* LNK P16 to P15 */

iolinker.sendBuf(iolinker_config, sizeof(iolinker_config));