I am using STM8 mcu , i want put a 15 minute counter or set timer to check some conditions in MCU so how i can do this?

[SJain.6]

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[Tesla DeLorean]

If it has a 1ms (1 KHz) ticker, count those off for the desire period. Perhaps use a TIM to count off minutes? Perhaps an RTC with an ALARM?

Which STM8? I think they make more than one, and they often have slightly different feature mixes.

https://www.st.com/resource/en/application_note/an3133-using-the-stm8l05xxxstm8l101xxstm8l15xxxstm8l162xxstm8al31xxstm8al3lxx-realtime-clock-stmicroelectronics.pdf