Rainbow Electronics MAXQ3120 - Manual (Page 21)

MAXQ3120
High-Precision ADC
Mixed-Signal Microcontroller
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System Timing
The MAXQ3120 generates its internal system clock
from an external high-frequency crystal. Because the
MAXQ3120 includes internal capacitors for this pur-
pose, no external capacitors are required to use the
high-frequency crystal. The MAXQ3120 should not be
driven directly by an external clock source.
A crystal warmup counter enhances operational relia-
bility. Each time the external crystal oscillation must
restart, such as after exiting stop mode, the device initi-
ates a crystal warmup period of 65,536 oscillations.
This allows time for the crystal amplitude and frequency
to stabilize before using it as a clock source.
Power Management
Advanced power-management features minimize power
consumption by dynamically matching the processing
speed of the device to the required performance level.
This means device operation can be slowed and power
consumption minimized during periods of reduced
activity. When more processing power is required, the
microcontroller can increase its operating frequency.
Software-selectable clock-divide operations allow flexi-
bility, selecting whether a system clock cycle is 1, 2, 4,
or 8 oscillator cycles. By performing this function in soft-
ware, a lower power state can be entered without the
cost of additional hardware.
For extremely power-sensitive applications, two addi-
tional low-power modes are available.
• Divide-by-256 power-management mode (PMM)
(PMME = 1, CD1:0 = 00b)
• Stop mode (STOP = 1)
In PMM, one system clock is 256 oscillator cycles, signifi-
cantly reducing power consumption while the microcon-
troller functions at reduced speed. The optional
switchback feature allows enabled interrupt sources,
such as the external interrupts and USARTs, to cause the
processor to quickly exit PMM mode and return to a
faster internal clock rate.
Figure 2. Clock Sources
MAXQ3120
GLITCH-FREE
MUX
DIV 1 DIV 2 DIV 4 DIV 8 PWM
CLOCK
DIVIDER
SELECTOR
DEFAULT
WATCHDOG
TIMER
RESET DOG
RWT
RESET
POWER-ON
RESET
STOP
STOP
POWER-ON
RESET
SWB
INTERRUPT/SERIAL PORT
RESET
STOP
POWER MONITOR
REAL-TIME CLOCK
LCD CONTROLLER
WATCHDOG RESET
CLOCK
GENERATION
SYSTEM CLOCK
ENABLE
WATCHDOG INTERRUPT
32kHz
CRYSTAL
CRYSTAL
MONITOR
ENABLE
INPUT
HF
CRYSTAL
CRYSTAL KILL
XDOG
STARTUP
TIMER
CLK INPUT
RESET
XDOG COUNT
XDOG DONE