Maxim Integrated MAX32600, Руководство пользователя

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MAX32600 User’s Guide System Clock, Timers/Counters, Watchdog Timers and Real Time Clock 10.1 System Clock
of the current system clock rate. Also, this provides a more variable (and not externally observable) clock to reduce the opportunity for an attacker to perform power
or timing analysis attacks against the cryptographic and security functions.
10.1.2 System Clock Configuration
The MAX32600 clock subsystem provides a high degree of flexibility to optimize an embedded system implementation. The user has options to trade-off external
components depending on the circuitry required by the desired application(s). A block diagram of the MAX32600 clock subsystem is provided in the figure above.
10.1.3 System Clock Sources
The internal clock circuitry generates the system clock from one of the three clock sources:
1. External Clock
2. Internal Oscillator with an external crystal or resonator
3. Internal Relaxation Oscillator
The register controls for the clocks are in the Clock Manager ( CLKMAN Registers ). There, clock sources can be selected and/or gated off and clock scalars can be
selected. In general, most clocks are disabled by default to minimize total system power consumption. Refer to the Clock Manager Register Map for details.
The external clock and crystal are mutually exclusive since they are input via the same clock pin. The clock subsystem is configured through the CLKMAN_CLK_CTRL
register; the primary clock source selection is made using the CLKMAN_CLK_CTRL.system_source_select register field.
Field Setting Primary Clock Source Selection
b00 24Mhz Relaxation Oscillator divided by eight
b01 24Mhz Relaxation Oscillator
b10 High Frequency Crystal Oscillator
b11 48Mhz PLL divided by two
The Relaxation Oscillator accuracy is sufficient to run the core on-chip digital logic and all external peripherals. For Real Time Clock (RTC) functionality, a 32kHz
XTAL/Resonator is required. For the USB peripheral, a frequency-accurate clock is required. This functionality can be provided by an external high-frequency crystal
oscillator or, if a 32kHz XTAL/Resonator is available, the Relaxation Oscillator can be used after firmware frequency calibration is performed.
An external high-frequency crystal (HFXTAL) may be required to achieve the highest precision ADC measurements. The most accurate ADC performance is obtained
when an 8MHz HFXTAL is used as the system clock source. However, in low sample rate ADC applications, the internal Relaxation Oscillator may be adequate.
Rev.1.3 April 2015 Maxim Integrated Page 501