N78E517A Datasheet, PDF (106/141 Pages) List of Unclassifed Manufacturers – Microcontroller

N78E517A Data Sheet
21. POWER MONITORING
In order to prevent incorrect execution during power up and power drop, N78E517A provides three power mon-
itor functions, power-on detection, Brown-out detection, and low power detection.
21.1 Power-on Detection
The power-on detection function is designed for detecting power up after power voltage reaches to a level
about 2.0V where the system can work. After power-on detected, the POF (PCON.4) will be set 1 to indicate a
cold reset, a power-on reset complete. The POF flag can be cleared via software.
21.2 Brown-out Detection
The other power monitoring function, Brown-out detection circuit is for monitoring the V_DD level during execu-
tion. There are four programmable Brown-out trigger levels available for wide voltage applications. The four
nominal levels are 2.2V, 2.7V, 3.8V, and 4.5V selected via setting CBOV[1:0] in CONFIG2. When V_DD drops to
the selected Brown-out trigger level (V_BOD), the Brown-out detection logic will either reset the CPU or request a
Brown-out interrupt. The user may determine Brown-out reset or interrupt enable according to different applica-
tion systems.
The Brown-out detection will request the interrupt while V_DD drops below V_BOD while BORST (PMC.4) is 0. In
this case, BOF (PMC.3) will set as a 1. After the user cleared this flag whereas V_DD remains below V_BOD, BOF
will not set again. BOF just acknowledge the user a power drop occurs. The BOF will set 1 after V_DD goes
higher than V_BOD to indicate a power resuming. The Brown-out circuit provides an useful status indicator BOS
(PMC.0), which is helpful to tell a Brown-out event or power resuming event occurrence. If BORST bit is set,
this will enable Brown-out reset function. After a Brown-out reset, BORF (RSR.2) will set 1 via hardware. It will
not be altered by reset other than power-on. Software can clear this bit. V_BOD has a hysteresis of 20-200mV.
The Brown-out detection circuit also provides a low power Brown-out detection mode for power saving. When
LPBOD is set 1, the Brown-out detection repeatedly senses the power voltage about every 12.8ms. For the
interval counting, the internal 10kHz RC oscillator will turn on in Brown-out low power mode. Note that the hys-
teresis feature will disappear in low power Brown-out detection mode.
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