Waveshare 2-CH RS485 HAT & RP2350-PiZero Communication Library

A high-performance dual-channel RS485 communication library and example suite for the 2-CH RS485 HAT, specifically ported and optimized for the Raspberry Pi RP2350 (Pico 2).

This project leverages the SC16IS752 SPI-to-Dual-UART bridge to provide two independent RS485 channels with automatic hardware flow control, managed via a clean C-based configuration layer or a lightweight MicroPython driver.

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📸 Hardware Overview

The 2-CH RS485 HAT is an expansion board designed for the Raspberry Pi form factor, featuring:

• Dual RS485 Channels: Fully independent communication on two ports.
• SC16IS752 Controller: High-speed SPI interface to dual UART, offloading UART processing from the main MCU.
• Level Conversion: Built-in logic level conversion for stable 3.3V/5V operation.
• Onboard Protection: TVS (Transient Voltage Suppressor) and lightning protection.

🛒 Purchase Links

• Module: Waveshare 2-CH RS485 HAT
• Controller: Waveshare RP2350-PiZero

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✨ Key Features

• Multi-Language Support: Full implementation for both C/C++ (Pico SDK) and MicroPython.
• Native RP2350 Support: Optimized for the new RP2350 (Pico 2) architecture.
• Dual-Channel Management: Simple API to initialize and control both RS485 channels independently.
• Direction Control: Dedicated TXDEN pins for manual or automatic half-duplex direction switching.
• Comprehensive Examples: Includes robust dual-channel ping-pong communication tests for both languages.
• Efficient SPI Interface: High-speed communication with the SC16IS752 bridge.

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🛠 Hardware Mapping (RP2350)

The library is configured to use the following GPIO pins on the RP2350 (mapped to the standard 40-pin header):

Component	Function	RP2350 GPIO	Header Pin (Pi Zero)
SPI	MISO	GP19	Pin 35
SPI	MOSI	GP20	Pin 38
SPI	SCK	GP21	Pin 40
SPI	CS	GP18	Pin 12
IRQ	Interrupt	GP24	Pin 18
RS485	TXDEN 1	GP27	Pin 13
RS485	TXDEN 2	GP22	Pin 15

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🚀 Getting Started

1. C/C++ SDK (Pico SDK)

Navigate to the RP2350 folder to build the firmware.

Prerequisites

• Raspberry Pi Pico SDK (v2.1.0 or higher)
• CMake (3.13+)
• GCC ARM Embedded Toolchain

Build Instructions

Linux/macOS:

cd RP2350
mkdir build && cd build
cmake ..
make -j$(nproc)

Windows:

cd RP2350
mkdir build
cd build
cmake -G "MinGW Makefiles" ..
cmake --build . -j4

Tip

Recommended for Windows: Use the Raspberry Pi Pico VS Code Extension. It handles the environment setup automatically.

🎯 Build Targets

• rs485_hat.uf2: Compiled from examples/main.c. Single-channel communication entry point.
• rs485_pingpong.uf2: Compiled from examples/dual_ping_pong.c. Comprehensive test for CH1 ↔ CH2 communication.

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2. MicroPython

Navigate to the Micropython folder.

Prerequisites

• MicroPython Firmware installed on your RP2350.
• A MicroPython IDE (like Thonny or VS Code with Pymakr).

Installation

1. Copy Micropython/sc16is752.py (the driver) to your board.
2. Run Micropython/main.py to start the dual-channel ping-pong test.

Usage Example

from sc16is752 import RS485Port, SC16IS752

# Initialize the SPI-to-UART bridge
bridge = SC16IS752(cs_pin=18, irq_pin=24)

# Setup RS485 Channels
ch1 = RS485Port(bridge, SC16IS752.CHANNEL_A, txden_pin=27, baudrate=9600)
ch2 = RS485Port(bridge, SC16IS752.CHANNEL_B, txden_pin=22, baudrate=9600)

# Transmit and Receive
ch1.write("Hello World")
data = ch2.read_line()

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📂 Project Structure

• RP2350/ - Main development folder for Pico SDK (C/C++).
  • lib/ - Core driver files for RS485 and SC16IS752.
  • lib/Config/ - Hardware abstraction layer and pin definitions.
  • examples/ - Ready-to-run C demo applications.
• Micropython/ - MicroPython implementation.
  • sc16is752.py - Lightweight MicroPython driver for the SPI bridge.
  • main.py - MicroPython loopback/ping-pong demo.

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🧪 Demo: Dual Channel Ping-Pong

The ping-pong test (available in both C and MicroPython) verifies the hardware by looping data between the two channels.

Wiring Instructions:

1. Connect CH1 A to CH2 A.
2. Connect CH1 B to CH2 B.

Expected Output: The program will transmit "Hello from CH1" and verify receipt on CH2, then perform the reverse. All logs are output via USB Serial (stdio) at 115200 baud.

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👤 Author

Developed and ported by the Waveshare team & community contributors.

📄 License

This project is licensed under the MIT License.