Wire1 with PCF8575 on UNO R4 only runs once

[PickyBiker]

The code below is the PCF8575 library Wire2 test using the Arduino UNO R4 WIFI. It works the first time I upload the code, but on subsequent uploads it fails to connect. To recover, it needs to have the USB-C connect unplugged and plugged in again. Then it works the first time again.

I modified the code to use Wire1 because that is what the Quiic connector uses.

Is this something in the code, the Wire library or the R4?

PCF8575_Wire1.ino

//
//    FILE: PCF8575_Wire1.ino
//  AUTHOR: Rob Tillaart
//    DATE: 2021-01-03
// PUPROSE: demo

#include "PCF8575.h"

// adjust addresses if needed
PCF8575 PCF(0x21, &Wire1);

void setup()
{
  Serial.begin(115200);
  Serial.println(__FILE__);
  Serial.print("PCF8575_LIB_VERSION:\t");
  Serial.println(PCF8575_LIB_VERSION);

  if (!PCF.begin())
  {
    Serial.println("could not initialize...");
  }
  if (!PCF.isConnected())
  {
    Serial.println("=> not connected");
    while(1);
  }

  int x = PCF.read16();
  Serial.print("Read ");
  Serial.println(x, HEX);
  delay(1000);
}

void loop()
{
  Serial.println("HLT");
  while (Serial.available() == 0);
  switch (Serial.read())
  {
    case 'H': doHigh(); break;
    case 'L': doLow(); break;
    case 'T': doToggle(); break;
  }
}

void doHigh()
{
  PCF.write(4, HIGH);
  int x = PCF.read16();
  Serial.print("Read ");
  Serial.println(x, HEX);
}

void doLow()
{
  PCF.write(4, LOW);
  int x = PCF.read16();
  Serial.print("Read ");
  Serial.println(x, HEX);
}

void doToggle()
{
  PCF.toggle(4);
  int x = PCF.read16();
  Serial.print("Read ");
  Serial.println(x, HEX);
}

[PickyBiker]

This problem does not exist today. The only thing I can think of is that I rebooted the system this morning.

[gilshultz]

Consider posting an annotated schematic showing exactly how you have wired it. It sounds like a hardware problem.

[PickyBiker]

gilshultz, although this isn't happening today after a reboot, here is what you were looking for.

The PCF8575 is connected like this:

[gilshultz]

This tells me nothing. Pin numbers, labels, etc are missing as well as showing what wire goes where.

[PickyBiker]

Qwiic connectors and cables by Sparkfun are designed to make it easy to string together I2C devices. The R4 in my project has a qwiic connector and the ICM-20948 IMU device has 2 of them. The PCF device doesn't have Qwiic connectors, it has 5-pin connector like this
That is connected but the cable with the Qwiic connector on one end and the 4 female Dupont connectors on the other.

You can get more information about Quiic here: Qwiic Connect System - SparkFun Electronics

Here is the updated image showing the connections.

[gilshultz]

The pictures do not work for me. Try this link: How to Read a Schematic - SparkFun Learn Also realize I probably do not have the same hardware as you do and my things look different.

[PickyBiker]

Good idea, how can we move it to the R4 WIFI forum?

[PerryBebbington]

Moved as requested.

[PickyBiker]

This issue continues to happen randomly, so please regard it as an open problem.

Thanks.