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# Clock Port

The Sentinel 65X clock port is a small, 28-pin female pin header on the mainboard, which exposes the system's debug serial line, I2C bus, reset and main interrupt lines, `PHI2` clock signal, and a 64-address memory-mapped I/O region, mapped to memory beginning at `0x00DFC0`. This region of uncommitted expansion is reserved for the use of user-installed clock port accessories.

## Pinout

| Pin  | Label |     | Label  | Pin  |
| :--- | :----:| --- | :----: | ---: |
| 1    |  GND  |     | +3.3V  | 2    |