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GPIO Protocol Configuration

Overview​

FREE-WILi's GPIO header supports multiple digital communication protocols. Each protocol can be configured through the settings menu and operates independently on dedicated pin sets.

SPI Configuration​

Pin Assignment​

  • Pin 1: Chip Select (CS) - Output
  • Pin 12: RX (MISO) - Input
  • Pin 13: TX (MOSI) - Output
  • Pin 15: SCLK - Output

SPI Parameters​

Frequency Configuration:

  • Range: Up to 70 MHz
  • Default: 5 MHz
  • Configuration: Via settings menu

Clock Polarity and Phase:

  • CPOL: Programmable clock polarity
  • CPHA: Programmable clock phase

I2C Configuration​

Pin Assignment​

  • Pin 8: SCL (Clock) - Bidirectional
  • Pin 10: SDA (Data) - Bidirectional

I2C Parameters​

Frequency Configuration:

  • Range: Up to 1 MHz
  • Default: 100 kHz (Standard mode)
  • Supported: Standard (100 kHz), Fast (400 kHz), Fast+ (1 MHz)

Pull-up Resistors:

  • Built-in: Software-controlled 10kΩ pull-ups on PCA9517 buffer
  • Control: Enable/disable via settings menu
  • Voltage: Matches V PINS IN level

UART Configuration​

Pin Assignment​

  • Pin 5: RX (Receive) - Input
  • Pin 7: CTS (Clear To Send) - Input
  • Pin 9: TX (Transmit) - Output
  • Pin 11: RTS (Request To Send) - Output

UART Parameters​

Baud Rate:

  • Range: Up to 8,000,000 bps
  • Default: 115,200 bps
  • Configuration: Programmable via settings menu

Data Format:

  • Data Bits: 4-16 bits (default: 8)
  • Parity: None, Even, Odd (default: None)
  • Stop Bits: 1-2 (default: 1)
  • Flow Control: RTS/CTS handshaking available (default: disabled)

Full Duplex: Simultaneous transmit and receive operations supported.

Protocol Interaction​

Concurrent Protocol Operation​

Supported Combinations:

  • All three protocols (SPI, I2C, UART) can operate simultaneously
  • No hardware conflicts between protocols
  • Independent configuration and operation

Shared Resources:

  • All protocols share the same V PINS IN voltage level
  • Logic analyzer can monitor all protocols

Configuration Examples​

High-Speed SPI Setup​

Settings Menu > SPI Configuration:
- Frequency: 20 MHz
- CPOL: 0 (Clock idle low)
- CPHA: 0 (Sample on rising edge)

Fast I2C Configuration​

Settings Menu > I2C Configuration:
- Frequency: 400 kHz (Fast mode)
- Pull-ups: Enabled

High Baud Rate UART​

Settings Menu > UART Configuration:
- Baud Rate: 2,000,000 bps
- RTS Hand Shaking: Enabled
- CTS Hand Shaking: Enabled
- Data Bits: 8
- Parity: None
- Stop Bits: 1

Related documentation: