I've been working for some time to get an Adafruit data logging shield that includes a PCF8523 RTC to work with a DUE. The shield and essentially the same sketch do work with a MEGA. The shield includes 1K pull-up resistors for both SDA1 and SCL1.
The only differences I've been able to identify between operation of the two boards is that different versions of Wire.h are used. Testing has identified that both SDA1 and SCL1 go to a constant 3.3 volts during start-up. All bits of the TWI_SR register are 1.
I am using IDE 2.0.3.
In reading various posts on this topic, I get the impression that I2C interfaces with the DUE can be touchy, but I could not identify specifics to look for.
In the attached sketch until I get to line 86 and I get a Serial.print indicating RTClib did not start.
Data_Log_Due.ino (7.8 KB)
Some assistance or areas for me to look at would be appreciated.
Thanks