| Pin | Description |
|---|---|
| Digital 0 | Serial RX |
| Digital 1 | Serial TX |
| Digital 2 | RFM12B Interrupt (INT 0) - if installed |
| Digital 3 |
Interrupt / Wake Up Alarm Output from MCP7941x - if installed Enable ports 3 & 4 on the L293D - if installed and if JP4 is shorted between 2 and 3. |
| Digital 4 |
Slave Select for SD Card - if installed Input 1 for L293D - if installed |
| Digital 5 | Input 2 for L293D - if installed |
| Digital 6 |
LED Input 3 for L293D - if installed |
| Digital 7 | Input 4 for L293D - if installed |
| Digital 8 | Spare and available for use |
| Digital 9 |
Slave Select for 23K256 SRAM (DIP) - if installed Enable ports 1 & 2 on the L293D - if installed Enable ports 3 & 4 on the L293D - if installed and if JP4 is shorted between 1 and 2. |
| Digital 10 | Slave Select for RFM12B - if installed |
| Digital 11 | SPI bus: Shared MOSI (Master Output, Slave Input) |
| Digital 12 | SPI bus: Shared MISO (Master Input, Slave Output) |
| Digital 13 | SPI bus: Shared Serial Clock (output from master) |
| Analog 0 | Spare and available for use - on screw terminals with up to 16v inputs |
| Analog 1 | Spare and available for use - on screw terminals with up to 16v inputs |
| Analog 2 | Spare and available for use - on screw terminals with up to 16v inputs |
| Analog 3 | Spare and available for use - on screw terminals with up to 16v inputs |
| Analog 4 | I2C Bus: SDA (data) |
| Analog 5 | I2C Bus: SCL (clock) |