Ok, after switching to a DS1340Z chip, the RTC Clock Plug now works:
Sample output:
I first ran a sketch to set the time, then commented out the setting part and uploaded it again. As you can see, the time kept ticking – just as in real life…
And it keeps going on its internal battery while power is disconnected:
That’s the whole point of this plug!
The battery holder is not perfect. The type I got is for surface mounting, but the board is for a narrower through-hole type. Had to snip the sides of this one off a bit, and it didn’t solder on quite as intended:
But it works. The spring action is very strong and pushes the battery to the board anyway.
The code for this RTC Plug has been added to the Ports library as “rtc_demo” example, and is available here.