The internal expansion interface features a mikroBUS™ compatible socket and extra I/O, power supply and control lines on two additional rows on the side, with standard 2.54 mm (.100 in) headers.
| EXT-B | mikroBUS socket |
EXT-A | ||
| Description | Pin | Pin | Description | |
| Main Supply | VIN |  |
GPIO1 | Generic IO |
| Expansion IO | IO1 | GPIO2 | Generic IO | |
| Expansion IO | IO2 | TX | UART Tx | |
| Modem Supply | 4V | RX | UART Rx | |
| RTC Supply | VRTC | PWM | PWM Out | |
| Shutdown | SHDN | ADC | Analog In | |
| Boot | BOOT | DAC1 | Analog IO | |
| Reset | NRST | DAC2 | Analog In | |