110 lines
3.5 KiB
Markdown
110 lines
3.5 KiB
Markdown
# 2x4 Programming Header Pinout
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## Header J2 - 2x4 Programming Header (8 Pins Total)
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This is a standard 2-row, 4-column header (2.54mm pitch) commonly used for programming headers.
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### Physical Layout
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```
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Top View:
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┌─────────────┐
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│ 1 2 3 4 │ ← Top row
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│ 5 6 7 8 │ ← Bottom row
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└─────────────┘
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```
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**Pin Numbering:**
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- Top row (left to right): Pins 1, 2, 3, 4
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- Bottom row (left to right): Pins 5, 6, 7, 8
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### Pin Assignment
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| Pin | Signal | ESP32 Connection | Description |
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|-----|--------|------------------|-------------|
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| **1** | **+3V3** | +3V3 Power Rail | Optional - Power ESP32 from programmer |
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| **2** | **GND** | GND | Ground reference (required) |
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| **3** | **UART_TX** | GPIO1 (UART0 TX) | ESP32 transmits to programmer |
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| **4** | **UART_RX** | GPIO3 (UART0 RX) | ESP32 receives from programmer |
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| **5** | **DTR** | GPIO0 | Data Terminal Ready (auto-reset) |
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| **6** | **RTS** | EN | Request To Send (auto-reset) |
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| **7** | **NC** | - | Not connected (spare) |
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| **8** | **NC** | - | Not connected (spare) |
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### Connection to USB-to-Serial Adapter
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| USB-to-Serial Pin | J2 Pin | Signal | Notes |
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|-------------------|--------|--------|-------|
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| VCC (3.3V) | Pin 1 | +3V3 | Optional - only if powering ESP32 from adapter |
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| GND | Pin 2 | GND | **Required** - always connect |
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| RX | Pin 3 | UART_TX | Adapter RX receives from ESP32 TX |
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| TX | Pin 4 | UART_RX | Adapter TX sends to ESP32 RX |
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| DTR | Pin 5 | DTR | Auto-reset control |
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| RTS | Pin 6 | RTS | Auto-reset control |
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| - | Pin 7 | NC | Spare (not used) |
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| - | Pin 8 | NC | Spare (not used) |
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**Important Notes:**
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- **RX/TX are swapped** - Adapter RX connects to ESP32 TX (Pin 3), and vice versa
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- **Do NOT connect VCC** if ESP32 is already powered from J1 (JST connector)
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- **Always connect GND** - critical for proper operation
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- **DTR and RTS** enable automatic reset (no button pressing needed)
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### Advantages of 2x4 Header
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1. **Standard layout** - Common 2.54mm pitch header format
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2. **More stable** - 2-row design is more mechanically stable
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3. **Spare pins** - Pins 7 and 8 available for future expansion
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4. **Easy to connect** - Standard programming cable format
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5. **Prevents wrong orientation** - 2-row design makes it harder to connect backwards
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### KiCad Symbol
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**Library:** `Connector_PinHeader_2.54mm`
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**Symbol:** `PinHeader_2x04_P2.54mm_Vertical`
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### Optional Pull-up Resistors
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For maximum reliability, add pull-up resistors:
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- **R5**: 10kΩ between J2 Pin 5 (DTR) and +3V3
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- **R6**: 10kΩ between J2 Pin 6 (RTS) and +3V3
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Most USB-to-Serial adapters have built-in pull-ups, but adding them on the board ensures reliable operation.
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### Flashing Process
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1. Connect USB-to-Serial adapter to J2 header (pins 1-6)
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2. Power the board (via J1 JST connector or J2 Pin 1)
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3. Use `esptool` or ESPHome to flash:
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```bash
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esptool.py --port /dev/ttyUSB0 write_flash 0x0 firmware.bin
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```
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4. DTR/RTS signals automatically put ESP32 into boot mode
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5. No button pressing required!
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### Future Expansion
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Pins 7 and 8 are spare and can be used for:
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- Additional UART (if needed)
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- I2C (SDA/SCL) for debugging
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- SPI (MISO/MOSI) for additional peripherals
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- GPIO monitoring
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- Or leave as NC (Not Connected)
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---
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## Summary
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**2x4 Header Layout:**
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```
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Top Row: VCC GND TX RX
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Bottom Row: DTR RTS NC NC
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```
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**6 pins used** (1-6) for programming
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**2 pins spare** (7-8) for future use
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This is a standard, stable, and convenient programming header configuration!
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