# Interfaces and Pinout

The board uses two MCUs. Both chips have the same pin definition. Each MCU
manages two CAN/CAN FD interfaces, two RS485 interfaces, one USB interface, and
one external SPI slave interface.

## Pins on Each MCU

| Function | MCU pins | Description |
| --- | --- | --- |
| FDCAN1 RX / TX | `PB8` / `PB9` | First CAN/CAN FD interface |
| FDCAN2 RX / TX | `PB5` / `PB6` | Second CAN/CAN FD interface |
| RS485-A TX / RX / RE | `PC4` / `PB7` / `PD2` | USART1, first RS485 interface |
| RS485-B TX / RX / RE | `PD5` / `PD6` / `PC9` | USART2, second RS485 interface |
| External SPI CS / SCK / MISO / MOSI | `PD0` / `PD1` / `PD3` / `PD4` | SPI2 slave, connected to the external host |
| Internal SPI CS / SCK / MISO / MOSI | `PA4` / `PA5` / `PA6` / `PA7` | SPI1, board-level connection between the two MCUs |
| Debug UART TX / RX | `PB10` / `PB11` | USART3 |
| I²C SCL / SDA | `PA9` / `PA10` | I2C1 |
| ADC input 1 / 2 | `PB0` / `PB1` | ADC1 channels 8 / 9 |
| LED1 / LED2 | `PA3` / `PC5` | Active low |
| USB DM / DP | `PA11` / `PA12` | USB composite device |
| SWDIO / SWCLK | `PA13` / `PA14` | ST-LINK programming and debugging |
| HSE OSC_IN / OSC_OUT | `PF0` / `PF1` | External 8 MHz crystal |
| Reserved input | `PC10` | Factory firmware configures this as floating input |

## External SPI Settings

| Item | Value |
| --- | --- |
| Mode | Slave |
| SPI mode | Mode 0 |
| Bit order | MSB First |
| Data width | 8 bit |

## Secondary Development Framework

The existing SANPO SPINE capabilities are retained. External sensors and other
devices can be expanded through UART, I²C, and ADC.

## Custom Development Framework

Use this framework for custom functionality. The project already configures the
functional pins of both MCUs, so application logic can be developed directly.

## Wiring Notes

- Install suitable termination resistors at both ends of a CAN/CAN FD bus. Do
  not reverse CAN_H and CAN_L.
- RS485 A/B naming may be reversed between vendors. If communication fails,
  check the transceiver markings and wiring.
- Connect USB, the SPI host, and external devices to a common ground.
- The two MCUs have independent USB and SWD interfaces. Do not mix them during
  firmware updates or debugging.