Timer1 external oscillator for RTC on PIC18F47j13

[PCM programmer]

I believe he actually means Epson Toyocom.

There is no Epson MC-164, so I conclude it is likely this one:
https://www5.epsondevice.com/en/products/crystal_unit/mc146.html
According to the data sheet on that page, the loads available are
6pf, 9pf, and 12.5pf.

Also, a 0 parameter in setup_rtc_alarm() does not mean no alarms.
It means no repeat alarms. With 0, you will get one alarm only.
With 10, you get the initial alarm and then 10 repeats.

[Ttelmah]

Good. The ESR on this is nicely in the required range.
However, if he has the 7pF version, he will probably have this much
capacitance without any add on capacitors. Even the 9pF one will only
want something like 10pF for the external capacitors.

[HaveAchat]

Sorry for delay in getting back to you, been dragged out into the sunshine for a few days!
The datasheet PCM found is correct. I had thought I had ordered the 12.5pF device but it looks like I have the 7pF version.

Every little error adds up!

[Ttelmah]

OK. The 7pF versions are designed basically to work without extra capacitors.
Typically the chip has a pin capacitance around 3 to 4pF. If you then have a
couple of cm of trace, with a power plane round it on both sides, you have
perhaps another 5pF. The crystal itself will have a pin capacitance of
perhaps 3pF, so the effective load capacitance will be:

(4+5+3)/2 = 6pF

Very close to the 7pF.

In fact some of the RTC clock chips are specifically specified to work
correctly with the 7pF crystals, with a specific board layout, and no extra
capacitors.

No wonder it is overloaded with the extra capacitors though!...