# CH32-16-CH-EXT

A simple CH32V003-based extension board providing 16 outputs (2x 74HC595), primarily designed for controlling [Chinese 16-relay modules](https://www.uctronics.com/download/Amazon/U604302_print.pdf) ([archive](https://web.archive.org/web/20220709045418/https://www.uctronics.com/download/Amazon/U604302_print.pdf)) over RS485. Uses 64-byte internal flash page for state persistence.

KiCad hardware design files are in the `hw` directory.

![photo](img/ch32_extension_photo.jpg)
![render](img/ch32_extension.png)

## Communication Protocol

### Message Format

The RS485 communication uses a simple 4-byte message format:

```
Byte 0: Board Address (0x01-0xFE, 0xFF for broadcast)
Byte 1: Command (0x01 for SET_OUTPUTS)
Byte 2: Data High Byte
Byte 3: Data Low Byte
```

### Protocol Constants

```c
#define BOARD_ADDRESS   0x01        // Default board address
#define CMD_SET_OUTPUTS 0x01        // Command to set outputs
#define BROADCAST_ADDR  0xFF        // Broadcast address
```

### Example Message

To control the outputs, send a 4-byte message:

```rust
let message = [
    address,            // Board address (0xFF for broadcast)
    CMD_SET_OUTPUTS,    // Command
    (value >> 8) as u8, // Data high byte
    value as u8,        // Data low byte
];
```