According the datasheet of the MCU RA4M1 there is a VBATT pin (Pin 4) for battery backup function. The ideal solution for the RTC.
In the UNO R4 Minima schematic this VBATT pin is connected to +5V.
On the UNO R4 Wifi the VBATT is available on a header pin labeled with VRTC.
For a RTC project I will keep the current time without setting the time after every power off.
Why is the VBATT pin missing on the Minima?
This is a terrible design choice and has effectively ruled out the Minima for use with the onboard RTC. Also tying the VBATT pin to +5v has made it hard to do a mod to access the pin as well. The only option I can see is to use an external RTC, which is such a waste.
You, are totally right.
I don't understand this design either.
On the Uno R4 Wifi the VBAT is connected to an external pin.
Why not on the UNO R4 Minima?
2 posts were split to a new topic: Is there a more elegant way to set time on internal RTC?
Looks like Arduino cut every possible cost from Minima. No ENIG PCB, no RTC header, no qwiic, EVEN NO POLYFUSE on USB!
I have tried the internal RTC. The drift is very big. I use a ds3231 that cost nothing connected with I2C bus and very accurate.
That's because there's no external 32.768kHz crystal on the board. Instead the R4 uses the RA4M1's much less accurate, 32kHz-ish, low speed on-chip LOCO oscillator.
Try this Arduino UNO R4 WiFi VRTC & OFF Pins