Real time Clock and Non-Volatile RAM options

I tried to do the same using a DS1216E ROM Smartwatch, but with zero success. Could be faulty component or bad programming on my side. I can dig up and share the code here if someone is interested.

The documentation, schematics, and pictures for interfacing a DS12C887 RTC chip are here. link github.com/ytmytm/c64-ds12c887

Maybe that can be of help.

Yes, I had the ROM version, put in the U36 socket. I tried with and without adding a ROM chip with some (working) utility software on top of it and wrote some assembler code to set and read time from the RTC, following the official documentation I found on-line, but it never worked for me. Again, it could be just me: I'm not an expert at 6502 assembler programming at all!

So looking at the docs for my chip, which by the way is quite different from the ones mentioned here that require funky access to get to the RTC data (mine just puts it in the ram) I noticed the only real difference is A14 has moved because of the Vpp and R/W pins.

So I will need to either make a PCB adapter or just lift those 3 pins before inserting the chip and solder jumper wires onto them.

My only question is this, how does the system know to map in the U36 ROM space? Does it look for code in the rom like a cartridge or is there a keycheck in the boot sequence?

I will obviously need to bank in the U36 space in order to read the RTC ram locations. The plan is to put this code in the non-volatile ram itself but for initial testing I just want to manually bank it in and see if I can see the contents of those memory locations.

Now, I assume as when it's active writes are sent only to the "shadow" ram underneath that anything written will come back as 00 (or ff? Not sure what fills the ram to start with!) rather than what I write, which is hidden in the real ram?

So I can test if it's banked in correctly simply by writing and reading from the those memory locations?

Anyway, rambling. Will update when I have some tests in the bank.