Maxim Integrated 2-14
MAX31782 User’s Guide
Revision 0; 8/11
2.7 Clock Generation
The MAX31782 generates its 4MHz instruction clock using an internal oscillator. This oscillator starts up when V
DD
exceeds the brownout voltage level, V
BO
. There is a delay of approximately 1000 clock cycles (t
SU:MOSC
) between
when the oscillator starts and when clocking of the MAX31782 begins. This delay ensures that the clock is stable prior
to beginning normal operation.
2.8 Power Modes
The MAX31782 has two modes of operation. These two modes of operation are detailed in the state diagram as shown
in Figure 2-6.
1) Normal CPU mode
2) Stop mode
The MAX31782 enters stop mode when the STOP bit in the system clock control register (CKCN) is set. Upon entering
stop mode, the digital core is no longer clocked, thus making the core inactive. In stop mode, the ADC is also disabled
and the Supply Voltage Monitor (SVM) can be disabled. The internal oscillator, brownout detection, and regulators
(REG18 and REG25 pins) remain active during stop mode. Table 2-2 details the state of the MAX31782’s analog and
digital blocks during the different modes of operation.
The MAX31782 exits stop mode when any of the following interrupt conditions occurs:
• GPIO interrupt from Port 6
• I
2
C START interrupt
• SVM interrupt
• External reset
The interrupt sources listed must be enabled prior to entering stop mode if they are going to be used to bring the
MAX31782 out of stop mode. After receiving one of these interrupts, the MAX31782 exits stop mode and returns to CPU
mode within 10 system clock cycles. If an interrupt causes the system to come out of stop mode, the program execution
starts from the point where stop mode was asserted. However, if an external reset is used to come out of stop mode,
the program execution begins from utility ROM location 8000h.
Table 2-2. State of Circuits During Different Modes
CKCN.STOP SVM.SVMEN SVM.SVMSTOP
POWER
MODE
CPU
REGULATORS
INTERNAL
OSCILLATOR
BROWNOUT
DETECTION
SVM
MONITOR
ADC
1.8V 2.5V
0 0 X
CPU
Mode
On On On On On Off On/Off
0 1 X
CPU
Mode
On On On On On On On/Off
1 0 X
Stop
Mode
Off On On On On Off Off
1 1 0
Stop
Mode
Off On On On On Off Off
1 1 1
Stop
Mode
Off On On On On On Off
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