adafruit_ds1307 module does not respect user-changed values for Square Wave output

[coplate]

I am working on a project with my rp2040 where I am using my DS1307 to trigger an interrupt every 1 second.
I had started this project in MicroPython with another library, and had updated register 07 in the DS1307 with the flags to generate a 1Hz square wave. ( set bits in register to '00010000' ).

When I started updating my project to use CircuitPython, I imported this library and found that it used those bits to validate if it is a 1307, which will not work.

This pull request is to update the module to reflect the specifications provided by the manufacture for which fields are constant.

[ladyada]

@caternuson any thoughts?

[caternuson]

This seems OK. But a little curious how one runs into this.

@coplate Are you restarting your code without a power cycle? Wondering how the check gets back anything from the register other than the expected power on defaults?

[coplate]

This seems OK. But a little curious how one runs into this.

@coplate Are you restarting your code without a power cycle? Wondering how the check gets back anything from the register other than the expected power on defaults?

@caternuson
My DS1307 has had a battery hooked up since I set it up a few weeks ago, so the IC itself has not had a power cycle. I kept the battery in to keep the clock accurate. I can imagine that previous tests on this would have passed if there wasn't a battery in the device, and it was relying on VCC power instead of VBAT. (If those tests including changing the SQW feature )

[caternuson]

oh yah, the battery. thanks. makes sense.

just dumping some datasheet info for ref:

there's really no dedicated who-am-i register. the existing check is making a flawed assumption that RS1 and RS0 will be power on defaults. using the always-read-0 bits seems like a better approach. and adding a second register (0x03) read should help to verify.

LGTM