====== STM32U0 Notes ======

===== Literature =====

  * Datasheets
    * [[https://www.st.com/resource/en/datasheet/stm32u031f4.pdf|DS14581 STM32U031x4/6/8]]
    * [[https://www.st.com/resource/en/datasheet/stm32u073c8.pdf|DS14548 STM32U073x8/B/C]]
    * [[https://www.st.com/resource/en/datasheet/stm32u083kc.pdf|DS14463 STM32U083xC]]
  * Application Notes
    * [[https://www.st.com/resource/en/application_note/an5938-getting-started-with-stm32u0-mcus-hardware-development-stmicroelectronics.pdf|AN5938 Getting started with STM32U0 MCUs hardware development]]
    * [[https://www.st.com/resource/en/application_note/an2606-stm32-microcontroller-system-memory-boot-mode-stmicroelectronics.pdf|AN2606 STM32 microcontroller system memory boot mode]]
  * Reference Manual
    * [[https://www.st.com/resource/en/reference_manual/rm0503-stm32u0-series-advanced-armbased-32bit-mcus-stmicroelectronics.pdf|RM0503 Reference manual]]

===== Development Boards =====

  - [[https://www.st.com/en/evaluation-tools/nucleo-u083rc.html|Nucleo-U083RC]] (STM32U083RCT6)
    * Purchasing
      * [[https://sg.element14.com/stmicroelectronics/nucleo-u083rc/dev-board-32bit-arm-cortex-m0/dp/4377835|S$21.68 at element14]]
    * User Manuals
      * [[https://www.st.com/resource/en/user_manual/um1727-getting-started-with-stm32-nucleo-board-software-development-tools-stmicroelectronics.pdf|UM1727 Getting started with STM32 Nucleo board software development tools]]
      * [[https://www.st.com/resource/en/user_manual/um3256-stm32-nucleo64-boards-mb1932-stmicroelectronics.pdf|UM3256 STM32 Nucleo-64 boards (MB1932)]]
  - [[https://www.st.com/en/evaluation-tools/stm32u083c-dk.html|STM32U083C-DK]] (STM32U083MC)
    * Purchasing
      * [[https://sg.element14.com/stmicroelectronics/stm32u083c-dk/discovery-kit-32bit-arm-cortex/dp/4377838|S$37.06 at element14]]
    * User Manuals
      * [[https://www.st.com/resource/en/user_manual/um3292-discovery-kit-with-stm32u083mc-mcu-stmicroelectronics.pdf|UM3292 Discovery kit with STM32U083MC MCU]]
      * [[https://www.st.com/resource/en/user_manual/um3313-stm32cubeu0-stm32u083cdk-demonstration-firmware-stmicroelectronics.pdf|UM3313 STM32CubeU0 STM32U083C-DK demonstration firmware]]

===== Operating Conditions =====

  * VDDx
    * 1.71 ≤ VDDx ≤ 3.60 V (absolute maximum: 4.00 V)
    * Nucleo-083RC LEDs become very dim when 3.3V net falls below 1.80 V
  * Brownout Reset((RM0503, §3.7.7 FLASH option register (FLASH_OPTR), Bits 10:8 BOR_LEV[2:0]: BOR reset level))
    * Selectable: 1.7, 2.0, 2.2, 2.5 or 2.8 V

===== Native USB (STM32U073, STM32U083) =====

In order to use the native USB for programming on pins PA11 and PA12, the following settings **must** be done in STM32CubeProgrammer --> Option bytes --> User Configuration.

^ Option byte name  ^ Value  ^ Description ^ Notes ^
| NBOOT_SEL  | 0 (Unchecked)  | BOOT0 pin (legacy mode) | :!: Factory setting is 1. You must change it to 0 to keep USB DFU programming capability. :!: |
| nBOOT1 | 1 (Checked) | Boot from Flash if BOOT0 = 1, otherwise System Memory | This is the factory setting |
| NRST_MODE | 1 or 3 | 1: Reset input only\\ 3. Bidirectional reset: The NRST pin is configured in reset input/output (legacy) mode | 3 is the factory setting |

===== STM32duino LowPower & RTC =====

^ State  ^ Peripherals ^ Memory ^ Voltage Supplies (VDDx) ^ STM32RTC::LSI_CLOCK  ^ STM32RTC::LSE_CLOCK :!: ^ STM32RTC::HSE_CLOCK :!: ^
| LowPower.idle() | On | On | On | Supported | Supported | Supported |
| LowPower.sleep() | On | On | On | Supported | Supported | Supported |
| LowPower.deepSleep() | On | On | On | Supported | Supported | Supported |
| LowPower.shutdown() :!: | Off | Off | Off |   | Supported |   |

:!:: External hardware required

==== Prerequisites for LowPower.shutdown() ====

  * External 32.768 kHz crystal for LSE((DS14581/DS14548/DS14463, §6.3.7 External clock source characteristics, Low-speed external clock generated from a crystal resonator))
  * <code>rtc.setClockSource(STM32RTC::LSE_CLOCK);
rtc.begin();</code>

==== RTC Clock Sources ====