Mitsubishi DS907x SIP User Manual page 64

USER'S GUIDE
threshold, the Power On Reset cycle will be executed as
before. As a result, no special processing is required in
software to accommodate this case.
In the case that V dips without going below V
CC
PFW flag will be set and a Power Fail Warning interrupt
will still occur when V
CC
old. The PFW flag will remain set until it is cleared by ei-
ther a reset of the flag by the software or by a Power On
cycle. If it is cleared while V
threshold, it will be immediately set again. If it is cleared
after V has risen back above the V
CC
SECURE MICROCONTROLLER POWER MANAGEMENT Figure 7–3
RESET VECTOR
POR = 0?
YES
SET POR
PFW = 1?
YES
LONG POWER–UP
SLEW RATE, KEEP
CHECKING
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drops below the V thresh-
PFW
is still below the V
CC
threshold,
PFW
NO
RUN NORMAL
RESET ROUTINE
NO
SET EPFW
POWER–FAIL
INTERRUPT
POWER ON
BOOT ROUTINE
then it will remain cleared until the next time V
below V .
PFW
As long as the PFW flag is set, an interrupt condition is
, the defined if EPFW is set. If the software executes a ser-
LI
vice routine in response to a PFW interrupt and exits the
service routine with the PFW flag still set, then the pro-
cessor will be immediately interrupted again. In a typical
application, however, the Power Fail Interrupt service
routine would test the PFW flag in a conditional loop to
PFW
determine if V
then return control to the main program in response to
the event. See Figure 7–3 for details.
POWER–FAIL WARNING
INTERRUPT VECTOR
POWER HAS FALLEN BELOW VPFW,
CLEAR PFW FLAG BY READING
SAVE CRITICAL DATA TO NVRAM;
PREPARE FOR POWER FAILURE
VOLTAGE IS STILL BELOW
VPFW, NOT SAFE TO RUN
64
has risen back above V
CC
(READ PCON)
NO
PFW = 1?
YES
goes
CC
and would
PFW
POWER HAS
RETURNED,
RESUME
OPERATION