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Merge branch 'docs/update_rtc_clock_source_description_in_api_references' into 'master'

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docs: update the description for RTC Clock Sources for esp32 and esp32s2

Closes DOC-530

See merge request espressif/esp-idf!10577
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Krzysztof Budzynski
2020-09-24 15:31:53 +08:00
parent 068690e604 a50966cf7a
commit b07a60c0b8
3 changed files with 17 additions and 14 deletions
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docs/en/api-reference/system/system_time.rst
+8 -5
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@@ -1,6 +1,9 @@
System Time
===========
{IDF_TARGET_RTC_CLK_FRE:default="150kHz", esp32="150kHz", esp32s2="90kHz"}
{IDF_TARGET_HARDWARE_DESIGN_URL:default="`ESP32 Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32_hardware_design_guidelines_en.pdf#page=10>`_", esp32="`ESP32 Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32_hardware_design_guidelines_en.pdf#page=10>`_", esp32s2="`ESP32-S2 Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32-s2_hardware_design_guidelines_en.pdf#page=10>`_"}
Overview
--------
@@ -27,17 +30,17 @@ RTC Clock Source
The RTC timer has the following clock sources:
- ``Internal 150kHz RC oscillator`` (default): Features lowest deep sleep current consumption and no dependence on any external components. However, as frequency stability is affected by temperature fluctuations, time may drift in both Deep and Light sleep modes.
- ``Internal {IDF_TARGET_RTC_CLK_FRE} RC oscillator`` (default): Features lowest deep sleep current consumption and no dependence on any external components. However, as frequency stability is affected by temperature fluctuations, time may drift in both Deep and Light sleep modes.
- ``External 32kHz crystal``: Requires a 32kHz crystal to be connected to the 32K_XP and 32K_NP pins. Provides better frequency stability at the expense of slightly higher (by 1 uA) Deep sleep current consumption.
- ``External 32kHz crystal``: Requires a 32kHz crystal to be connected to the 32K_XP and 32K_XN pins. Provides better frequency stability at the expense of slightly higher (by 1 uA) Deep sleep current consumption.
- ``External 32kHz oscillator at 32K_XP pin``: Allows using 32kHz clock generated by an external circuit. The external clock signal must be connected to the 32K_XP pin. The amplitude should be less than 1.2 V for sine wave signal and less than 1 V for square wave signal. Common mode voltage should be in the range of 0.1 < Vcm < 0.5xVamp, where Vamp is signal amplitude. Additionally, a 1 nF capacitor must be placed between the 32K_XN pin and ground. In this case, the 32K_XN pin cannot be used as a GPIO pin.
- ``External 32kHz oscillator at 32K_XN pin``: Allows using 32kHz clock generated by an external circuit. The external clock signal must be connected to the 32K_XN pin. The amplitude should be less than 1.2 V for sine wave signal and less than 1 V for square wave signal. Common mode voltage should be in the range of 0.1 < Vcm < 0.5xVamp, where Vamp is signal amplitude. Additionally, a 1 nF capacitor must be placed between the 32K_XP pin and ground. In this case, the 32K_XP pin cannot be used as a GPIO pin.
- ``Internal 8.5MHz oscillator, divided by 256 (~33kHz)``. Provides better frequency stability than the ``internal 150kHz RC oscillator`` at the expense of higher (by 5 uA) deep sleep current consumption. It also does not require external components.
- ``Internal 8.5MHz oscillator, divided by 256 (~33kHz)``: Provides better frequency stability than the ``internal {IDF_TARGET_RTC_CLK_FRE} RC oscillator`` at the expense of higher (by 5 uA) deep sleep current consumption. It also does not require external components.
The choice depends on your requirements for system time accuracy and power consumption in sleep modes. To modify the RTC clock source, set :ref:`CONFIG_{IDF_TARGET_CFG_PREFIX}_RTC_CLK_SRC` in project configuration.
More details on wiring requirements for the ``External 32kHz crystal`` and ``External 32kHz oscillator at 32K_XP pin`` sources can be found in Section 2.1.4 *Crystal Oscillator* of `Hardware Design Guidelines <https://www.espressif.com/sites/default/files/documentation/esp32_hardware_design_guidelines_en.pdf#page=10>`_.
More details on wiring requirements for the ``External 32kHz crystal`` and ``External 32kHz oscillator at 32K_XN pin`` sources can be found in Section *Crystal Oscillator* of {IDF_TARGET_HARDWARE_DESIGN_URL}.
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