I try to communicate, read and write, from Arduino - slave - to RPi - master - with Android Things.

If i R/W, with a level converter, from RPi to Arduino 5v (16Mhz), everything works fine.

So i decide to eliminate the level converter, and use a 3v3 Arduino mini pro (8Mhz).

The write works fine, but when i try to read from the Arduino, the signal stops.

[5v\_16Mhz](https://i.stack.imgur.com/9M96g.png)  

After the Setup to 9, 0 address, and reads to 9, the signal still low and received the data. No problem.

[3v3\_8Mhz](https://i.stack.imgur.com/mQfEN.png)  

After the Setup to 9, 0 address, and read to 9, the signal goes high and the data stop.

I used the same example for the Slave:

```
#include <Wire.h>

byte RFID[20] = {9,8,7,6,5,4,3,2,1,1,2,3,4,5,6,7,8,9,1,2};

void setup() {
  Wire.begin(8);          // join i2c bus with address #8
  Wire.onRequest(requestEvent); // register event
  Wire.onReceive(receiveEvent); // register event
  Serial.begin(115200);     // start serial for output
  pinMode(13, OUTPUT);
}

void loop() {
  delay(100);
}

// function that executes whenever data is requested by master
// this function is registered as an event, see setup()
void requestEvent() {
  Serial.println("Master ask");
  digitalWrite(13, HIGH);
  delay(250);
  Wire.write(RFID, 20);
  digitalWrite(13, LOW);
}

// function should be executes whenever data is received from master
// this function is registered as an event, but it's called every time the RPi
// call the Device.
void receiveEvent(int howMany) {
  while (0 < Wire.available()) {
    byte RTC_syn = Wire.read(); // receive byte
    Serial.println(RTC_syn);
  }
}

```

I really don't know how drives the signal high...  

Someone can help me?