| 1 | ID | Pin to communicate with the ID chip on an extension board |
| 2 | GND | Ground |
| 3 | ADC(+) | Analog-to-Digital Converter; alternatively, a pin for the positive
terminal of a differential ADC |
| 4 | ADC(-) | Analog-to-Digital Converter; alternatively, a pin for the negative
terminal of a differential ADC |
| 5 | GPIO1 | General purpose I/O pin |
| 6 | GPIO2 | General purpose I/O pin |
| 7 | PWM(+) | Pulse Width Modulation; alternatively, a pin for the positive part of
a differential PWM |
| 8 | PWM(-) | Pulse Width Modulation; alternatively, a pin for the negative part of
a differential PWM |
| 9 | IRQ/GPIO | Interrupt request pin and/or general purpose I/O pin |
| 10 | SPI_SS_B/ GPIO | Host select pin for Serial Peripheral Interface (SPI) and/or general
purpose I/O pin |
| 11 | I2C_SDA | Data pin for I2C interface. Always connected, bus type |
| 12 | I2C_SCL | Clock pin for I2C interface. Always connected, bus type |
| 13 | UART_RX | Receiver pin of target device UART |
| 14 | UART_TX | Transmitter pin of target device UART |
| 15 | SPI_SS_A | Client select for SPI. This pin should preferably not be connected to
anything else |
| 16 | SPI_MOSI | SPI host out, client in pin. Always connected, bus type |
| 17 | SPI_MISO | SPI host in, client out pin. Always connected, bus type |
| 18 | SPI_SCK | SPI clock pin. Always connected, bus type |
| 19 | GND | Ground pin for extension boards |
| 20 | VCC | Power pin for extension boards |
