Power Domain

A 5 V micro-USB conncetor feeds the MIC5219-3. produces a clean 3.3 V rail. A green indicator LED confirms the rail is alive.

USB 5 V ──► LDO 3.3 V ──► VDD, VDDA
                    └──► LED (330 Ω → GND)

Clock Tree

The MCU can boot from three sources:

• HSI – internal 8 MHz RC, ±1 %
• HSE – external 8 MHz crystal, ±20 ppm
• PLL – multiplies HSE to 72 MHz

Typical configuration:

8 MHz HSE ──► HSE ──► PLL×9 ──► SYSCLK 72 MHz
──► AHB 72 MHz
                                                └──► APB1 36 MHz
                                                └──► APB2 72 MHz

Crystal load capacitance: 22 pF on each leg to ground.

Programming Interface

SWD (Serial Wire Debug) is preferred. Only three pins are required:

• SWDIO (PA13)
• SWCLK (PA14)
• nRESET

Add 100 kΩ pull-up on SWDIO and 10 kΩ pull-down on SWCLK for reliability.

Reset Network

nRESET is held high by a 10 kΩ resistor and pulled low by a push-button. A 100 nF capacitor debounces the switch and ensures a clean power-on reset.

3.3 V ──► 10 kΩ ──► nRESET ─┬──► MCU
                            ├──► Push-button → GND
                            └──► 100 nF → GND

Boot Configuration

Tie both pins to GND through 10 kΩ resitsors for normal flash execution.

Complete Schematic Overview

1. Power: USB → LDO → MCU + LED
2. Clock: 8 MHz crystal + with 22 pF caps
3. Debug: SWD header (3 pins + GND)
4. Reset: RC network + push-button
5. Boot: BOOT0/BOOT1 pulled low

All VSS pins grounded; each VDD pair decoupled with 100 nF + 4.7 µF.

Quick Bring-Up Checklist

• 3.3 V present on VDD/VDDA
• 8 MHz oscillation on OSC_IN/OUT
• nRESET idles high, goes low when button pressed
• SWDIO/SWCLK accessible via header
• BOOT0/BOOT1 both low

Once the checklist passes, the device is ready for firmware upload and further peripheral expansion.