MCU wakeup from sleep by a timer

[enkavak]

Hello,

       I am using nRF52832 IC with softdevice and SDK v15.

       I wish to make the MCU in sleep mode and then a couple of milliseconds (let's say 250ms) wakes up the MCU. For this purpose, can I use the timer? Or do you have any idea ?

       

[haakonsh]

You'll want to use the RTC — Real-time counter. See the Real Time Counter Example and RTC API documentation. 

[enkavak]

Can I use it with the softdevice?

I have external xtal. Do I need to use "lfclk"?

In addition, does the resolution is second? I need resolution in milliseconds 

[haakonsh]

You can use RTC1-2. You can also use the Timer library (app_timer), see also Application Timer API docs. 

[enkavak]

will this awake the MCU from sleep mode?

I have external xtal. Do I need to use "lfclk"?

[haakonsh]

Any interrupt will wake the CPU. 

"I have external xtal. Do I need to use "lfclk"?"
- Well, yes for the RTC you ned a LF clock source. If you've got a 32kHz crystal you can use the LFXO as the source. .