SLAU367P October 2012 – April 2020 MSP430FR5041 , MSP430FR5043 , MSP430FR50431 , MSP430FR5847 , MSP430FR58471 , MSP430FR5848 , MSP430FR5849 , MSP430FR5857 , MSP430FR5858 , MSP430FR5859 , MSP430FR5867 , MSP430FR58671 , MSP430FR5868 , MSP430FR5869 , MSP430FR5870 , MSP430FR5872 , MSP430FR58721 , MSP430FR5887 , MSP430FR5888 , MSP430FR5889 , MSP430FR58891 , MSP430FR5922 , MSP430FR59221 , MSP430FR5947 , MSP430FR59471 , MSP430FR5948 , MSP430FR5949 , MSP430FR5957 , MSP430FR5958 , MSP430FR5959 , MSP430FR5962 , MSP430FR5964 , MSP430FR5967 , MSP430FR5968 , MSP430FR5969 , MSP430FR5969-SP , MSP430FR59691 , MSP430FR5970 , MSP430FR5972 , MSP430FR59721 , MSP430FR5986 , MSP430FR5987 , MSP430FR5988 , MSP430FR5989 , MSP430FR5989-EP , MSP430FR59891 , MSP430FR5992 , MSP430FR5994 , MSP430FR59941 , MSP430FR6005 , MSP430FR6007 , MSP430FR6035 , MSP430FR6037 , MSP430FR60371 , MSP430FR6041 , MSP430FR6043 , MSP430FR60431 , MSP430FR6045 , MSP430FR6047 , MSP430FR60471 , MSP430FR6820 , MSP430FR6822 , MSP430FR68221 , MSP430FR6870 , MSP430FR6872 , MSP430FR68721 , MSP430FR6877 , MSP430FR6879 , MSP430FR68791 , MSP430FR6887 , MSP430FR6888 , MSP430FR6889 , MSP430FR68891 , MSP430FR6920 , MSP430FR6922 , MSP430FR69221 , MSP430FR6927 , MSP430FR69271 , MSP430FR6928 , MSP430FR6970 , MSP430FR6972 , MSP430FR69721 , MSP430FR6977 , MSP430FR6979 , MSP430FR69791 , MSP430FR6987 , MSP430FR6988 , MSP430FR6989 , MSP430FR69891
3.1 Clock System Introduction
The clock system module supports low system cost and low power consumption. Using three system clock signals, the user can select the best balance of performance and power consumption. The clock module can be configured to operate without any external components, with one or two external crystals, or with resonators, under full software control.
The clock system module includes the following clock sources:
- LFXTCLK: Low-frequency oscillator that can be used either with low-frequency 32768-Hz watch crystals, standard crystals, resonators, or external clock sources in the 50 kHz or below range. When in bypass mode, LFXTCLK can be driven with an external square wave signal.
- VLOCLK: Internal very-low-power low-frequency oscillator with 10-kHz typical frequency
- DCOCLK: Internal digitally controlled oscillator (DCO) with selectable frequencies
- MODCLK: Internal low-power oscillator with 5-MHz typical frequency. LFMODCLK is MODCLK divided by 128.
- HFXTCLK: High-frequency oscillator that can be used with standard crystals or resonators in the 4‑MHz to 24-MHz range. When in bypass mode, HFXTCLK can be driven with an external square wave signal.
Four system clock signals are available from the clock module:
- ACLK: Auxiliary clock. The ACLK is software selectable as LFXTCLK, VLOCLK, or LFMODCLK. ACLK can be divided by 1, 2, 4, 8, 16, or 32. ACLK is software selectable by individual peripheral modules.
- MCLK: Master clock. MCLK is software selectable as LFXTCLK, VLOCLK, LFMODCLK, DCOCLK, MODCLK, or HFXTCLK. MCLK can be divided by 1, 2, 4, 8, 16, or 32. MCLK is used by the CPU and system.
- SMCLK: Subsystem master clock. SMCLK is software selectable as LFXTCLK, VLOCLK, LFMODCLK, DCOCLK, MODCLK, or HFXTCLK. SMCLK is software selectable by individual peripheral modules.
- MODCLK: Module clock. MODCLK may also be used by various peripheral modules and is sourced by MODOSC.
- VLOCLK: VLO clock. VLOCLK may also be used directly by various peripheral modules and is sourced by VLO.
NOTE
Not all devices contain both LFXT and HFXT clock sources. See the device-specific data sheet for availability.
Figure 3-1 shows the block diagram of the clock system module.
Figure 3-1 Clock System Block Diagram