ETRA SOM/ETRA Hardware/Peripherals/Real Time Clock

History
Issue Date	Notes
2020/12/31	First Release

Real Time Clock

This chapter describes the technical specifications and features for the RTC component on the ETRA module.

Features

The Real Time Clock available on ETRA SOM is based on STM32MP1 SoC.

The RTC supports the following standards and features:

• calendar with subsecond, seconds, minutes, hours (12 or 24 format), week day, date, month, year, in BCD (binary-coded decimal) format
• automatic correction for 28, 29 (leap year), 30, and 31 days of the month
• two programmable alarms
• digital calibration circuit with 0.95 ppm resolution, to compensate for quartz crystal inaccuracy
• timestamp feature which can be used to save the calendar content
• 17-bit auto-reload wakeup timer (WUT) for periodic events with programmable resolution and period
• the RTC clock sources can be:
  • a 32.768 kHz external crystal
  • an external resonator or oscillator
  • the internal low power RC oscillator
  • the high-speed external clock (HSE), divided by a prescaler in the RCC
• the RTC is functional in VBAT mode and in all low-power modes when it is clocked by the external crystal or oscillator
• the RTC is supplied through a switch that takes power either from the VDD supply when present or from the VBAT pin
• all RTC events (Alarm, WakeUp Timer, Timestamp) can generate an interrupt and wakeup the device from the low-power modes

Backup power is provided through the VBAT signal connected to J1.14, for more detail see the Pinout table section.

If not used, VBAT signal must be externally connected to the VDD rail.

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