# SparkFun Pro Micro - RP2040 as I2C slave?

**URL:** <https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095>\
**Category:** Other Microcontrollers\
**Created:** [November 21, 2021, 12:54pm UTC](https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095 "2021-11-21T12:54:47Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![pollux](https://avatars.discourse-cdn.com/v4/letter/p/53a042/32.png) [@pollux](https://community.sparkfun.com/u/pollux)\
**Post date:** [November 21, 2021, 12:54pm UTC](https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095/1 "2021-11-21T12:54:47Z")

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Is it possible, to use the SparkFun Pro Micro - RP2040 as slave with the I2C protocol? According to the RP2040 datasheet ([https://datasheets.raspberrypi.com/rp20 … asheet.pdf](https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf)) the microcontroller can be used as slave (see “4.3.1. Features”).

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**Author:** ![YellowDog](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/yellowdog/32/1782_2.png) [@YellowDog](https://community.sparkfun.com/u/YellowDog)\
**Post date:** [November 21, 2021, 4:26pm UTC](https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095/2 "2021-11-21T16:26:33Z")

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With the right code, I don’t see any reason why you couldn’t.

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<div class="post-metadata">

**Author:** ![pollux](https://avatars.discourse-cdn.com/v4/letter/p/53a042/32.png) [@pollux](https://community.sparkfun.com/u/pollux)\
**Post date:** [November 21, 2021, 7:30pm UTC](https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095/3 "2021-11-21T19:30:03Z")

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So, what is the right code?

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<div class="post-metadata">

**Author:** ![YellowDog](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/yellowdog/32/1782_2.png) [@YellowDog](https://community.sparkfun.com/u/YellowDog)\
**Post date:** [November 21, 2021, 10:52pm UTC](https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095/4 "2021-11-21T22:52:27Z")

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I don’t have any, you’d need to write your own.

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<div class="post-metadata">

**Author:** ![Ryan7777](https://avatars.discourse-cdn.com/v4/letter/r/3d9bf3/32.png) [@Ryan7777](https://community.sparkfun.com/u/Ryan7777)\
**Post date:** [December 18, 2022, 11:50pm UTC](https://community.sparkfun.com/t/sparkfun-pro-micro-rp2040-as-i2c-slave/43095/5 "2022-12-18T23:50:36Z")

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Yes, it can be. I have been using various examples for arduino IC2 coms for master/slave (search for it on your browser of choice) and it works on the regular qwiic connector just fine. I cannot, however, get to work using Wire1 on the second I2C port that is supposed to be available on RP2040 devices.

Anyway, this is what have been using for a simple test, modified examples from various sources:

Sending MCU Code:

int x = 0;

void setup() {

// Start the I2C Bus as Master

Wire.begin();

}

void loop() {

Wire.beginTransmission(9); // transmit to device #9

Wire.write(x); // sends x

Wire.endTransmission(); // stop transmitting

x++; // Increment x

if (x \> 5) x = 0; // `reset x once it gets 6

delay(500);

}

Receiving MCU Code:

#include \<Wire.h\>

#include \<Adafruit\_NeoPixel.h\>

#ifdef **AVR**

#include \<avr/power.h\> // Required for 16 MHz Adafruit Trinket

#endif

// Which pin on the Arduino is connected to the NeoPixels?

// On a Trinket or Gemma we suggest changing this to 1:

#define LED\_PIN 25

// How many NeoPixels are attached to the Arduino?

#define LED\_COUNT 1

// Declare our NeoPixel strip object:

Adafruit\_NeoPixel strip(LED\_COUNT, LED\_PIN, NEO\_GRB + NEO\_KHZ800);

// Argument 1 = Number of pixels in NeoPixel strip

// Argument 2 = Arduino pin number (most are valid)

// Argument 3 = Pixel type flags, add together as needed:

// NEO\_KHZ800 800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)

// NEO\_KHZ400 400 KHz (classic ‘v1’ (not v2) FLORA pixels, WS2811 drivers)

// NEO\_GRB Pixels are wired for GRB bitstream (most NeoPixel products)

// NEO\_RGB Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)

// NEO\_RGBW Pixels are wired for RGBW bitstream (NeoPixel RGBW products)

// setup() function – runs once at startup --------------------------------

int x = 0;

void setup() {

// These lines are specifically to support the Adafruit Trinket 5V 16 MHz.

// Any other board, you can remove this part (but no harm leaving it):

Serial.begin(9600);

strip.begin(); // INITIALIZE NeoPixel strip object (REQUIRED)

strip.show(); // Turn OFF all pixels ASAP

strip.setBrightness(50); // Set BRIGHTNESS to about 1/5 (max = 255)

Wire.begin(9);

// Attach a function to trigger when something is received.

Wire.onReceive(receiveEvent);

}

void receiveEvent(int bytes) {

x = Wire.read(); // read one character from the I2C

}

// loop() function – runs repeatedly as long as board is on ---------------

void loop() {

if (x == 1) {

strip.setPixelColor(0,255,0,0); // Set pixel’s color (in RAM) RED

strip.show();

// Fill along the length of the strip in various colors…

// colorWipe(strip.Color(255, 0, 0), 2000); // Red

// colorWipe(strip.Color( 0, 255, 0), 2000); // Green

// colorWipe(strip.Color( 0, 0, 255), 2000); // Blue

}

// Do a theater marquee effect in various colors…

// theaterChase(strip.Color(127, 127, 127), 100); // White, half brightness

// theaterChase(strip.Color(127, 0, 0), 100); // Red, half brightness

// theaterChase(strip.Color( 0, 0, 127), 100); // Blue, half brightness

if (x == 3) {

strip.setPixelColor(0,0,255,0); // Set pixel’s color (in RAM) GREEN

strip.show();

// rainbow(50); // Flowing rainbow cycle along the whole strip

// theaterChaseRainbow(50); // Rainbow-enhanced theaterChase variant

}

}

// Some functions of our own for creating animated effects -----------------

// Fill strip pixels one after another with a color. Strip is NOT cleared

// first; anything there will be covered pixel by pixel. Pass in color

// (as a single ‘packed’ 32-bit value, which you can get by calling

// strip.Color(red, green, blue) as shown in the loop() function above),

// and a delay time (in milliseconds) between pixels.

void colorWipe(uint32\_t color, int wait) {

for(int i=0; i\<strip.numPixels(); i++) { // For each pixel in strip…

strip.setPixelColor(i, color); // Set pixel’s color (in RAM)

strip.show(); // Update strip to match

delay(wait); // Pause for a moment

}

}

// Theater-marquee-style chasing lights. Pass in a color (32-bit value,

// a la strip.Color(r,g,b) as mentioned above), and a delay time (in ms)

// between frames.

void theaterChase(uint32\_t color, int wait) {

for(int a=0; a\<10; a++) { // Repeat 10 times…

for(int b=0; b\<3; b++) { // ‘b’ counts from 0 to 2…

strip.clear(); // Set all pixels in RAM to 0 (off)

// ‘c’ counts up from ‘b’ to end of strip in steps of 3…

for(int c=b; c\<strip.numPixels(); c += 3) {

strip.setPixelColor(c, color); // Set pixel ‘c’ to value ‘color’

}

strip.show(); // Update strip with new contents

delay(wait); // Pause for a moment

}

}

}

// Rainbow cycle along whole strip. Pass delay time (in ms) between frames.

void rainbow(int wait) {

// Hue of first pixel runs 5 complete loops through the color wheel.

// Color wheel has a range of 65536 but it’s OK if we roll over, so

// just count from 0 to 5\*65536. Adding 256 to firstPixelHue each time

// means we’ll make 5\*65536/256 = 1280 passes through this outer loop:

for(long firstPixelHue = 0; firstPixelHue \< 5\*65536; firstPixelHue += 256) {

for(int i=0; i\<strip.numPixels(); i++) { // For each pixel in strip…

// Offset pixel hue by an amount to make one full revolution of the

// color wheel (range of 65536) along the length of the strip

// (strip.numPixels() steps):

int pixelHue = firstPixelHue + (i \* 65536L / strip.numPixels());

// strip.ColorHSV() can take 1 or 3 arguments: a hue (0 to 65535) or

// optionally add saturation and value (brightness) (each 0 to 255).

// Here we’re using just the single-argument hue variant. The result

// is passed through strip.gamma32() to provide ‘truer’ colors

// before assigning to each pixel:

strip.setPixelColor(i, strip.gamma32(strip.ColorHSV(pixelHue)));

}

strip.show(); // Update strip with new contents

delay(wait); // Pause for a moment

}

}

// Rainbow-enhanced theater marquee. Pass delay time (in ms) between frames.

void theaterChaseRainbow(int wait) {

int firstPixelHue = 0; // First pixel starts at red (hue 0)

for(int a=0; a\<30; a++) { // Repeat 30 times…

for(int b=0; b\<3; b++) { // ‘b’ counts from 0 to 2…

strip.clear(); // Set all pixels in RAM to 0 (off)

// ‘c’ counts up from ‘b’ to end of strip in increments of 3…

for(int c=b; c\<strip.numPixels(); c += 3) {

// hue of pixel ‘c’ is offset by an amount to make one full

// revolution of the color wheel (range 65536) along the length

// of the strip (strip.numPixels() steps):

int hue = firstPixelHue + c \* 65536L / strip.numPixels();

uint32\_t color = strip.gamma32(strip.ColorHSV(hue)); // hue → RGB

strip.setPixelColor(c, color); // Set pixel ‘c’ to value ‘color’

}

strip.show(); // Update strip with new contents

delay(wait); // Pause for a moment

firstPixelHue += 65536 / 90; // One cycle of color wheel over 90 frames

}

}

}