4.1 XTAL1,XTAL2 Pin Configuration

For the ATmega328PB device, the PB6,PB7 can be multiplexed into the XTAL1,XTAL2 pin of internal inverting oscillator amplifier with clock fuse setting to Crystal oscillator as shown in the table below. As the table shows, an external clock can be input from the XTAL1 pin once the CKSEL fuse is programmed to “External clock” option.

Table 4-1. Device Clocking Options Select
Device clocking optionCKSEL[3:0]
Low Power Crystal Oscillator1111 - 1000
Low Frequency Crystal Oscillator0101 – 0100
Internal 128kHz RC Oscillator0011
Calibrated Internal RC Oscillator0010
External Clock0000
Reserved0001