SLAS887A September 2014 – May 2018
The clock system consists of a fixed 16.384-MHz frequency internal DCO. The DCO can operate in internal resistor mode or external resistor mode. The DCO clock accuracy is higher when operating in external resistor mode especially upon variation in operating temperature. This feature can be useful in applications like utility metering in which accurate clock is necessary under varying operating temperature. When external resistor mode is selected by application, the resistor of recommended value must be connected to ROSC pin of the device. Refer to Table 5-2 for the recommended value of resistor at ROSC pin. TI recommends connecting the ROSC pin to AVSS while operating DCO in internal resistor mode. When a resistor fault is detected in the external resistor mode, the DCO automatically switches to the internal resistor mode as a fail-safe mechanism to keep the system clocks active.
The DCO can be completely bypassed and the system clocks can be sourced by external digital clock. The clock system generates MCLK, SMCLK, and ACLK. MCLK is used by the CPU, while SMCLK and ACLK are used by the peripheral modules. There are programmable clock dividers for MCLK and SMCLK. ACLK runs at a fixed 32-kHz frequency. The clock system supports active mode and four low-power modes.