Connecting GPIOs

Connecting Your Caravel User Project to External Hardware Using GPIOs

When developing custom designs within the Caravel user project, General Purpose Input/Output (GPIO) pins are essential for interacting with the world outside your chip. These versatile pins allow your design to send and receive signals, connecting to everything from simple LEDs and switches to complex sensors and other integrated circuits.

Understanding Caravel's GPIOs

Caravel's GPIOs are highly adaptable and can be configured in several ways:

• Inputs: This setting allows your design to read signals from external devices. Imagine connecting a button; when pressed, the GPIO acts as an input, informing your design of the state change.

• Outputs: When configured as an output, your design can send signals to control external components. For instance, you could use an output GPIO to turn an LED on or off.

• Bidirectional: This advanced mode allows a single GPIO pin to dynamically switch between functioning as an input and an output. This is incredibly useful for communication protocols where data needs to flow in both directions over the same line.

Managing GPIO Direction with the Output Enable Bar (OEB)

The key to controlling a GPIO's behavior is the Output Enable Bar (OEB) signal. Each GPIO pin has its own OEB, which dictates whether the pin is configured for input, output, or is in a high-impedance state, allowing it to receive data without interference.

Here's how the OEB signal controls GPIO behavior:

• Configuring as an Input: To set a GPIO as an input, you must drive its OEB signal HIGH (1). This places the GPIO in a high-impedance state, effectively disconnecting your internal logic from the physical pin and allowing it to receive external signals without conflict.

• Configuring as an Output: To use a GPIO as an output, its OEB signal needs to be LOW (0). This enables your internal design to actively drive the voltage on the GPIO pin, sending signals to external components.

• Implementing Bidirectional GPIOs: For scenarios where a GPIO needs to alternate between sending and receiving data, you'll dynamically control its OEB signal.

  • When the OEB is LOW (0), the GPIO acts as an output, driven by your design.

  • When the OEB is HIGH (1), the GPIO transitions to an input, entering a high-impedance state to receive external data.

This dynamic control of the OEB allows for flexible communication with other devices using a single pin.

GPIO Configuration Summary

The table below summarizes how the OEB signal and your design's output determine the GPIO pin's behavior:

By effectively managing the OEB signal in your Verilog or VHDL code, you can unlock the full potential of Caravel's GPIOs, enabling seamless interaction between your custom design and the outside world.