The STK505 has support to easily configure the hardware to upport three different clock configurations.
External Clock
On board crystal
Internal Oscillator
The XTAL1 and XTAL2 pins are configured as regular I/O port pins when not used as clock input/output. The clock selection switch is used to connect the pins to different components depending on whether it is used as clock pins or I/O pins.
The device fuses must be programmed to use the selected clock source. See the device datasheet for more details.
| Position | Function |
|---|---|
| XTAL |
XTAL1 and XTAL2 pins connected to the XTAL socket. |
| EXT CLK |
XTAL1 pin connected to the STK500 clock source. XTAL2 pin connected to PORTB header. |
| INT RC |
XTAL1 and XTAL2 pins connected to the PORTB header. |