External Clock

To drive the device from an external clock source, CLKI should be driven as shown in the Figure below. To run the device on an external clock, the CLKMSR.CLKMS must be programmed to '0b10'.

Table 1. External Clock Frequency
Frequency CLKMSR.CLKMS
0 - 12MHz 0b10
Figure 1. External Clock Drive Configuration

When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure stable operation of the MCU. A variation in frequency of more than 2% from one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the MCU is kept in Reset during the changes.