Abov MC96FR364B, Руководство пользователя

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November, 2018 Rev.1.4 167
13.7 Brown Out Detector
The MC96FR364B includes a system to protect against low voltage conditions in order to preserve
memory contents and control MCU system states during supply voltage variations. The system is
comprised of a power-on-reset(nPOR) and an BOD with 4 voltage level indicators. The BOD is
enabled when BODEN in BODR is high. The BOD is auto-disabled upon entering STOP mode. This
auto-disable function reduces operating power noticeably consumed by BOD itself.
The BOD has two main functions. One is to generate a BOD stop level(=BODOUT0) and the other is
to indicate voltage levels above BOD stop level denoted by BODOUT1,2,3,4 each.
Remember that BOD itself does not generate a reset signal. When operating voltage drops below a
pre-defined level(V
BODOUT0
), the BOD does not cause the whole system to be reset, but signals main
chip to enter BOD(STOP) mode instantaneously. For more information about BOD stop, refer to
section 12.4 POWER MANAGEMENT.
Besides BOD stop level, the BOD gives four low voltage warning flags to indicate to the user that the
supply voltage is approaching, but is still above, the BOD stop level. These flags can be read through
the BODSR register, also can be an interrupt source when BODIEN bit in BODSR is set.
Like external reset, BODOUT0 is also filtered by a dedicated noise cancelling logic. A pulse shorter
than about 2us(typically) is ignored by the system in condition Vdd is between 1.75V and 5.5V.
BODLS[1:0]
RESET_BODB
Brown Out
Detector
BODOUT0
D s Q
CP
r
D Q
CP
r
DEBOUNCE
CLK
External VDD
BODEN
STOP MODE
BODRF
(BOD Reset Flag)
CPU
Write
SCLK
(System CLK)
nPOR
r Q
CP
STOP_OSCB
VDD Rise
VDC Lock
s
STOP_OSCB : Indicates STOP mode (active low signal)
VDC Lock : VDC Lock detect signal indicating that VDC is
stable after BOD(STOP) mode exit.
Figure 13-9 Block Diagram of BOD