GPIO Essentials

# GPIO Essentials

**GPIO** — General Purpose Input/Output. The most basic peripheral: making pins go high or low, and reading whether they're high or low.

## Configurations

Before you can use a GPIO pin, you need to decide *how* it will behave.

### Direction
- **Output** — you drive the pin (e.g., turn on an LED)
- **Input** — you read the pin (e.g., detect a button press)

### Output Modes
- **Push-pull** (default) — actively drives the pin high *and* low
- **Open-drain** — actively drives low, but *floats* when "high" (needs external pull-up)

### Pull Resistors (for inputs)
- **Pull-up** — pin reads high when nothing is connected; button pulls it low
- **Pull-down** — pin reads low when nothing is connected; button pulls it high
- **Floating** — no pull resistor; pin state is undefined when nothing is connected

### Drive Strength (for outputs)
How much current the pin can source or sink. Higher drive strength = brighter LED, but more power consumption.

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## Controls

### Output Controls
| Method | What It Does |
|--------|-------------|
| `set_high()` | Drive the pin high |
| `set_low()` | Drive the pin low |
| `toggle()` | Flip the pin state |
| `set_level(Level)` | Set to a specific level |
| `is_set_high()` | Check what you last set |

### Input Controls
| Method | What It Does |
|--------|-------------|
| `is_high()` → `bool` | Is the pin high? |
| `is_low()` → `bool` | Is the pin low? |
| `get_level()` → `Level` | Get the level as an enum |

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## uFerris GPIO Map

Check your **pinout card** for the exact pin assignments on the uFerris Megalops board:

| Function | Pin | Notes |
|----------|-----|-------|
| Onboard LED | GPIO? | Active high/low? |
| User Button | GPIO? | Needs pull-up? |
| I2C SDA | GPIO? | Used in Part 3 |
| I2C SCL | GPIO? | Used in Part 3 |

---

## Mapping to docs.rs

Here's how GPIO maps to the Create → Configure → Control pattern:

| Step | What to Look For | Where on docs.rs |
|------|-----------------|-----------------|
| **Create** | `Output::new(pin, level, config)` | Struct page → `impl Output` |
| **Configure** | `OutputConfig`, `InputConfig`, `Pull`, `DriveStrength` | Associated types / linked structs |
| **Control** | `set_high()`, `toggle()`, `get_level()` | Trait impls + inherent methods |

Now let's put this into practice.

The Embedded Rustacean · Rust Week 2026