HT46R49 Holtek Semiconductor, HT46R49 Datasheet - Page 37

• Manufacturer Part Number: HT46R49
• Description: Cost-Effective A/D Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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Rev. 1.30
RES Pin Reset
This type of reset occurs when the microcontroller is
already running and the RES pin is forcefully pulled
low by external hardware such as an external switch.
In this case as in the case of other reset, the Program
Counter will reset to zero and program execution initi-
ated from this point.
Low Voltage Reset
The microcontroller contains a low voltage reset circuit
in order to monitor the supply voltage of the device,
which is selected via a configuration option. If the supply
voltage of the device drops to within a range of
0.9V~V
tery, the LVR will automatically reset the device inter-
nally. The LVR includes the following specifications: For
a valid LVR signal, a low voltage, i.e., a voltage in the
range between 0.9V~V
value t
voltage state does not exceed 1ms, the LVR will ignore it
and will not perform a reset function.
Watchdog Time-out Reset during Normal Operation
The Watchdog time-out Reset during normal opera-
tion is the same as a hardware RES pin reset except
that the Watchdog time-out flag TO will be set to 1 .
Watchdog Time-out Reset during Power Down
The Watchdog time-out Reset during Power Down is
a little different from other kinds of reset. Most of the
conditions remain unchanged except that the Pro-
gram Counter and the Stack Pointer will be cleared to
Characteristics for t
WDT Time-out Reset during Normal Operation
0 and the TO flag will be set to 1 . Refer to the A.C.
LVR
LVR
Low Voltage Reset Timing Chart
specified in the A.C. characteristics. If the low
such as might occur when changing the bat-
RES Reset Timing Chart
Timing Chart
SST
LVR
LVR
details.
must exist for greater than the
HT46R46/C46/R47/C47/R48A/C48A/R49
37
Reset Initial Conditions
The different types of reset described affect the reset
flags in different ways. These flags, known as PDF and
TO are located in the status register and are controlled
by various microcontroller operations, such as the
Power Down function or Watchdog Timer. The reset
flags are shown in the table:
Note:
The following table indicates the way in which the vari-
ous components of the microcontroller are affected after
a power-on reset occurs.
The different kinds of resets all affect the internal regis-
ters of the microcontroller in different ways. To ensure
reliable continuation of normal program execution after
a reset occurs, it is important to know what condition the
microcontroller is in after a particular reset occurs. The
following table describes how each type of reset affects
each of the microcontroller internal registers. Note that
where more than one package type exists the table will
reflect the situation for the larger package type.
TO PDF
Program Counter
Interrupts
WDT
Timer/Event
Counter
Prescaler
Input/Output Ports I/O ports will be setup as inputs
Stack Pointer
0
u
1
1
WDT Time-out Reset during Power Down
u stands for unchanged
0
u
u
1
Item
RES reset during power-on
RES or LVR reset during normal operation
WDT time-out reset during normal operation
WDT time-out reset during Power Down
Timing Chart
Reset to zero
All interrupts will be disabled
Clear after reset, WDT begins
counting
Timer Counter will be turned off
The Timer Counter Prescaler will
be cleared
Stack Pointer will point to the top
of the stack
RESET Conditions
Condition After RESET
June 5, 2008