PCA21125 how can I set "interrupt output" right away?

[StrongOrange]

I would like to control the output of the PCA21125.

From what I have studied, there are four ways to set the interrupt output:
minute interrupts, second interrupts, alarm, and countdown.

However, I would like to set the interrupt output directly, regardless of these conditions.

I tried setting AF or TF via the Control 2 register, but it did not work.

So, my questions are:

1. Are AF and TF not set by the Tx command via SPI? Are AF and TF read-only?
2. If so, how can I distinguish between read-only register values and writable register values in the datasheet?
3. Is there a way to set the interrupt output by command right away?
   - I thought about using the countdown function and setting its countdown to a very short time, but the countdown function will be used for another purpose.
   - The second interrupt could also be a way, but it is too slow for the situation I want to use it for now.

[TomasVaverka]

Hi Jonggeun, 

The PCA21125 has an open-drain active low interrupt output and as you correctly stated it can be sourced from: second/minute timer, countdown timer and alarm function. There is no other option and it is not possible to activate the interrupt output via an SPI command.

BR, Tomas

[StrongOrange]

Thank you for your reply.

I think it is clear to say AF and TF cannot be set directly via SPI, it seems like read-only bits.

How can I figure out both bits or other register bits are read-only or the other are writable in the datasheet?

It seems like it is not written in the datasheet.