GPIO pin summary based on MCU schematic (U1)
| GPIO | Net | Function / description | Type | Notes |
|---|---|---|---|---|
| IO20 (RXD) | RX | UART0 data receive | UART | J1_Monitor1 pin 3 — serial monitor |
| IO21 (TXD) | TX | UART0 data transmit | UART | J1_Monitor1 pin 2 — serial monitor |
| IO18 | D− | USB D− (programming) | USB | J1_Prog1 pin 3 — flash via USB |
| IO19 | D+ | USB D+ (programming) | USB | J1_Prog1 pin 2 — flash via USB |
| IO4 | SCL | I2C clock | I2C | Pull-up R23 4.7 kΩ. Shared bus: DUSBSS ×4, INA226, TC74 |
| IO5 | SDA | I2C data | I2C | Pull-up R24 4,7 kΩ. Shared bus |
| IO3 | CLK | Shift register clock | SPI/SR | Shared with 74HC165 (read) + 74HC595 (write) |
| IO8 | GET | Shift register latch / load | SPI/SR | Data transfer latch pulse (PL / RCLK) |
| IO17 | Data_Out | MISO — data from shift registers | SPI/SR | From 74HC165 U18 QH′ — FAULT, ALERT, CC status |
| IO16 | Data_In | MOSI — data to shift register | SPI/SR | To 74HC595 U19 SER — outputs EN0–EN3, BZ |
| IO6 | PWM | PWM output for fan | GPIO/PWM | J1Fan1 pin 4 |
| IO7 | TACH | Fan tachometer (input) | GPIO | J1Fan1 pin 3 — pull-up R42 10 kΩ |
| IO10 | Boot | Boot mode | GPIO | J1_Control1 pin 1, pull-up R18 10 kΩ. LOW = download mode |
| IO2 | Enable | EN pin — reset/enable | GPIO | J1_Control1 pin 3, pull-up R17 10 kΩ |
| 3V3 (pin 1) | +3V3 | MCU power | PWR | From XC6220B331MR (U3) — 3.3 V LDO |
| GND (pin 9) | Earth | Ground | PWR | Common ground |
IO1, IO9, IO13 are marked × (NC). IO0 and IO11–IO15 are not used in the schematic.
Click bits to set simulated input states. U17 = ports 0+1 (bits 15–8), U18 = ports 2+3 (bits 7–0).
| Bit | Net | Port | Typ | Stav |
|---|
Click bits to build the output byte. Physical outputs switch only after a GET pulse.
| Bit | Output | Net | Target | State |
|---|
Combined view from both registers — set bits in the Read and Write tabs.
| Signal | Value | Register | Description |
|---|