ML51/ML54/ML56
Sep. 01, 2020
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ML51/M
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Series
Tec
hnical Reference
Manual
6.2.3
Power Monitering and Reset
The ML51/ML54/ML56 Series has several options to place device in reset condition. It also offers the
software flags to indicate the source, which causes a reset. In general, most SFR go to their Reset
value irrespective of the reset condition, but there are several reset source indicating flags whose
state depends on the source of reset. User can read back these flags to determine the cause of reset
using software. There are five ways of putting the device into reset state. They are power-on reset,
brown-out reset, external reset, WDT reset, and software reset.
Power-On Rese
（
POR
）
t and Low Voltage Reset (LVR)
6.2.3.1
The ML51/ML54/ML56 Series incorporates an internal power-on reset (POR) and a low voltage reset
(LVR). During a power-on process of rising power supply voltage V
DD
, the POR or LVR will hold the
MCU in reset mode when V
DD
is lower than the voltage reference thresholds. This design makes CPU
not access program Flash while the V
DD
is not adequate performing the Flash reading. If an
undetermined operating code is read from the program Flash and executed, this will put CPU and
even the whole system in to an erroneous state. After a while, V
DD
rises above the threshold where the
system can work, the selected oscillator will start and then program code will execute from 0000H. At
the same time, a power-on flag POF (PCON.4) will be set 1 to indicate a cold reset, a power-on
process complete. Note that the contents of internal RAM will be undetermined after a power-on. It is
recommended that user gives initial values for the RAM block.
The POF is recommended to be cleared to 0 via software to check if a cold reset or warm reset
performed after the next reset occurs. If a cold reset caused by power off and on, POF will be set 1
again. If the reset is a warm reset caused by other reset sources, POF will remain 0. User may take a
different course to check other reset flags and deal with the warm reset event. For detailed electrical
characteristics.