Wire library help needed just i2c address transmitted

Projects Programming
1

Trying to study the Wire library, I read some info taken from here.
As you all know, this really simple example changes the value of a AD5171 digital potentiometer via I2C. Written by Nicholas Zambetti and Shawn Bonkowski, demonstrates use of the Wire library.

I just copied and adapted the code below from the example. I am an experienced assembler and C/C++ programmer and hardware developer/designer.
Although several I2C devices like DS3231 RTC, etc. work fine using standard Arduino libraries, the mentioned example doesn't work for me in my working NANO board.
What am I doing wrong, please?

This code should transmit:
1 - first the I2C protocol device address - Start / 8 + 1bits
2 - 1 test instruction data byte
3 - 1 variable test byte constantly incremented
4 - I2C Stop condition

The only byte I can see in my oscilloscope is just the first one (picture attached). The 2 data bytes are not being transmited. If I reduce the transmission to just the step (2) instruction single data byte, same result is shown.

#include <Wire.h>

void setup() 
{
  Wire.begin(); // join i2c bus (address optional for master)
}

byte val = 0;

  void loop() 
{
  Wire.beginTransmission(44); // transmit to device #44 (0x2c)
  Wire.write(byte(0x55));     // sends instruction byte
  Wire.write(val++);          // sends potentiometer value byte
  Wire.endTransmission();     // stop transmitting
  delay(50);                  // some time delay for my oscilloscope
}

Arduino I2C
Arduino I2C1920×1437 216 KB

Thank you in advance
Robert

2

shouldn't that be 0x00 ? (from https://www.arduino.cc/en/Tutorial/LibraryExamples/DigitalPotentiometer)

3

Check the code returned by Wire.endTransmission().

Even if your scope screenshot looks differently the transmission abort may indicate that no slave responded to that I2C address. Run the I2c_scanner example to find out the real I2C address of your sensor.

4

Ahhhhhhhhh !
Thank you DrDiettrich, that must be the reason.
I will test this and return to report.
The documentation that I have available doesn't mention that the function aborts if no slave responds on the bus. The function must be checking the ACK/NACK mechanism, which is correct. My intention was to make an "open loop" test.

5

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