Reading from and writing to registers on an I2C device

[RickSeiden]

Hello,

I am attempting to write data to an i2c device and then read it back using Wire.h. I don't think it's device specific, but it's a DS1337C real time clock with an internal crystal. (I'm running an external RTC because I need two alarms and as far as I know the PICO's RTC only provides 1.) I have it wired with RTC SDA to PICO 8 and RTC SCL to PICO 9 with 1k resistors pulling both lines up to 3V3.

I start out with a fairly simple sketch

#include <Wire.h>

void setup() {

  Serial.begin(115200);
  delay(5000);
  
  
  Wire.setSDA(8);
  Wire.setSCL(9);
  Wire.begin();
  
}

void loop() {

  //write 0x11 to register 0x02
  Wire.beginTransmission(0x68);
  Wire.write(0x02);
  Wire.write(0x11);
  Wire.endTransmission();
  delay(1000);

  //read register 0x02
  Wire.beginTransmission(0x68);
  Wire.write(0x02);
  Wire.endTransmission();

  Wire.requestFrom(0x68, 1, true);
  byte returnValue;
  while (Wire.available()) {
    returnValue = Wire.read();
  }  
  Serial.print("read ");
  Serial.println(returnValue,HEX);
  
  //write 0x12 to register 0x02
  Wire.beginTransmission(0x68);
  Wire.write(0x02);
  Wire.write(0x12);
  Wire.endTransmission();
  delay(1000);
  
  //read register 0x02
  Wire.beginTransmission(0x68);
  Wire.write(0x02);
  Wire.endTransmission();

  Wire.requestFrom(0x68, 1, true);
  while (Wire.available()) {
    returnValue = Wire.read();
  }  
  Serial.print("read ");
  Serial.println(returnValue,HEX);
  
}

and everything works as I expect it to.

So now I want to reduce redundancy, so I throw the read and write code into some subroutines, giving this seconds sketch:

#include <Wire.h>

uint8_t _address = 0x68;

void setup() {
  Serial.begin(115200);
  delay(5000);


  Wire.setSDA(8);
  Wire.setSCL(9);
  Wire.begin();

}

void writeRegister(uint8_t myRegister, uint8_t myValue) {
  Wire.beginTransmission(_address);
  Wire.write(myRegister);
  Wire.write(myValue);
  Wire.endTransmission();
}

byte readRegister(uint8_t myRegister) {
  Wire.beginTransmission(_address);
  Wire.write(myRegister);
  Wire.endTransmission();

  Wire.requestFrom(_address, 1, true);
  byte returnValue;
  while (Wire.available()) {
    returnValue = Wire.read();
  }
  return returnValue;
}


void loop() {

  //write 0x11 to register 0x02
  writeRegister(0x02, 0x11);
  delay(1000);
  
  //read register 0x02
  Serial.print("read ");
  Serial.println(readRegister(0x02), HEX);

  //write 0x12 to register 0x02
  writeRegister(0x02, 0x12);
  delay(1000);
  
  //read register 0x02
  Serial.print("read ");
  Serial.println(readRegister(0x02), HEX);

}

Both of these give the same output:

20:17:30.078 -> read 11
20:17:31.104 -> read 12
20:17:32.086 -> read 11
20:17:33.115 -> read 12

So far so good, but I'd really like this to be in a library, so I write a library. First is the header file:

#ifndef WireRegister_h
#define WireRegister_h

#include <Arduino.h>

class WireRegister {
  public:
    WireRegister(uint8_t myAddress);
    byte readRegister(uint8_t myRegister);
    void writeRegister(uint8_t myRegister, uint8_t myValue);

  private:
    byte _address;
};

#endif

Next is the CPP file:

#include "WireRegister.h"
#include <Wire.h>

WireRegister::WireRegister(uint8_t myAddress){
  _address=myAddress;
  Wire.setSDA(8);
  Wire.setSCL(9);
  Wire.begin();
}

byte WireRegister::readRegister(uint8_t myRegister) {
  Wire.beginTransmission(_address);
  Wire.write(myRegister);
  Wire.endTransmission();

  Wire.requestFrom(_address, 1, true);
  byte returnValue;
  while (Wire.available()) {
    returnValue = Wire.read();
  }
  return returnValue;
}

void WireRegister::writeRegister(uint8_t myRegister, uint8_t myValue) {
  Wire.beginTransmission(_address);
  Wire.write(myRegister);
  Wire.write(myValue);
  Wire.endTransmission();
}

And finally is the sketch:

#include "WireRegister.h"

byte _address = 0x68;

WireRegister myRegister=WireRegister(_address);

void setup() {
  Serial.begin(115200);
  delay(5000);
}

void loop() {
  //write 0x11 to register 0x02
  myRegister.writeRegister(0x02, 0x11);
  delay(1000);

  Serial.print("read ");
  Serial.println(myRegister.readRegister(0x02), HEX);

  //write 0x12 to register 0x02
  myRegister.writeRegister(0x02, 0x12);
  delay(1000);

  Serial.print("read ");
  Serial.println(myRegister.readRegister(0x02), HEX);
}

As you can see, I've pretty much just moved the subroutines into the Class. The problem I have is that this gives the following output:

20:20:17.388 -> read 0
20:20:18.419 -> read 0
20:20:19.404 -> read 0
20:20:20.389 -> read 0

I have no idea why this isn't working in the class. I'm hoping that someone here can help me out, but I'm not sure if this is PICO specific or not.

Thanks

PS: Why don't I just use some of the pre-written libraries for the DS1307 which has the same registers and works the same way as the DS1337C? Because the libraries I've found don't address all of the features I want, and don't return the time and date in the way that I need. Some of them, for example, don't have a way of checking that an alarm has gone off. Others return the date and time in a format I don't want to use. I could write a wrapper around them, I suppose, but I'm trying to treat this as a learning experience rather than a means to an end.

[RickSeiden]

Hello again. I decided to do a little more testing, so I commented out the lines for Wire.setSDA and Wire.SCL in the first sketch and sent it to a clone of an Arduino Uno. It worked. So I did the same for the second sketch, and again it worked. Finally, I commented out the Wire.SDA and Wire.SCL lines in the class and uploaded the library version to the Uno clone, and it worked.

So the native Wire library that uses the same code with the exception of Wire.setSDA and Wire.setSCL works on an Uno clone, but the Wire library for the Pico W does not work in the Class.