Helios4 provide 12 GPIOs on J12 header that are free to use for user application. This header connected to 16-bit IO Expander [PCA9655E](http://www.onsemi.com/PowerSolutions/product.do?id=PCA9655E) using I2C bus 0.

| Pin | GPIO number | Remarks |
|------------|----------|---------|
| 1 | - | 3.3V supply |
| 2 | IO0_2 | |
| 3 | IO0_3 | |
| 4 | IO0_4 | |
| 5 | IO0_7 | |
| 6 | IO1_0 | |
| 7 | IO1_1 | |
| 8 | IO1_2 | |
| 9 | IO1_3 | |
| 10 | IO1_4 | |
| 11 | IO1_5 | |
| 12 | IO1_6 | |
| 13 | IO1_7 | |
| 14 | - | GND |
!!! warning
**IO0_0**, **IO0_1**, **IO0_5**, and **IO0_6** are reserved for system use. It is not advisable to access the I2C IO expander directly using I2C.
## LED Expansion (J18)
Helios4 board was designed to either use the on-board LEDs or use custom expansion panel (not-available). To use the header insure to switch to OFF the DIP switch SW2.