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Clock System Introduction
3.1
Clock System Introduction
The clock system module supports low system cost and low power consumption. By selecting from the
internal clock signals, the user can select the best balance of performance and low power consumption.
The clock module can operate without any external components, with one or two external crystals, or with
resonators, under full software control.
The clock system module includes up to five clock sources:
•
XT1CLK: Low-frequency or high-frequency oscillator that can be used with low-frequency 32768-Hz
watch crystals, standard crystals, resonators, or external clock sources in the 4 MHz to 24 MHz range.
When optional XT2 is present (see below), the XT1 high-frequency mode may or may not be available,
depending on the device configuration. See the device-specific data sheet for supported functions.
•
VLOCLK: Internal very-low-power low-frequency oscillator with 10-kHz typical frequency
•
DCOCLK: Internal digitally controlled oscillator (DCO) with three selectable fixed frequencies
•
XT2CLK: Optional high-frequency oscillator that can be used with standard crystals, resonators, or
external clock sources in the 4 MHz to 24 MHz range. See the device-specific data sheet for
availability.
Four system clock signals are available from the clock module:
•
ACLK: Auxiliary clock. The ACLK is software selectable as XT1CLK, VLOCLK, DCOCLK, and when
available, XT2CLK. 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 XT1CLK, VLOCLK, DCOCLK, and when
available, XT2CLK. 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 XT1CLK, VLOCLK, DCOCLK, and
when available, XT2CLK. SMCLK is software selectable by individual peripheral modules.
•
MODCLK: Module clock. MODCLK is used by various peripheral modules and is sourced by
MODOSC.
shows a block diagram of the clock system module.
71
SLAU272C – May 2011 – Revised November 2013
Clock System (CS)
Copyright © 2011–2013, Texas Instruments Incorporated