HT45R22E Holtek Semiconductor, HT45R22E Datasheet - Page 28

• Manufacturer Part Number: HT45R22E
• Description: Remote Type 8-bit OTP MCU
• Manufacturer: Holtek Semiconductor

Note: t
Note: t
Note: t
Rev. 1.00
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 cir-
cuit in order to monitor the supply voltage of the de-
vice. The LVR function is selected via a configuration
option. If the supply voltage of the device drops to
within a range of 0.9V~V
changing the battery, the LVR will automatically reset
the device internally. For a valid LVR signal, a low sup-
ply voltage, i.e., a voltage in the range between
0.9V~V
ified by t
ply voltage state does not exceed this value, the LVR
will ignore the low supply voltage and will not perform
a reset function. The actual V
lected via configuration options.
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 Idle/Sleep mode
The Watchdog time-out Reset during Idle/Sleep mode
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.
RSTD
RSTD
RSTD
LVR
Low Voltage Reset Timing Chart
LVR
is power-on delay, typical time=100ms
is power-on delay, typical time=100ms
is power-on delay, typical time=100ms
must exist for a time greater than that spec-
in the A.C. characteristics. If the low sup-
RES Reset Timing Chart
Timing Chart
SST
LVR
details.
LVR
such as might occur when
LVR
value can be se-
28
Note:
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
Idle/Sleep function or Watchdog Timer. The reset flags
are shown in the table:
Note: u stands for unchanged
The following table indicates the way in which the vari-
ous components of the microcontroller are affected after
a power-on reset occurs.
Program Counter
Interrupts
WDT
Timer/Event
Counter
Prescaler
Input/Output Ports I/O ports will be setup as inputs
Stack Pointer
TO
0
u
1
1
WDT Time-out Reset during Idle/Sleep
PDF
The t
clock cycles via configuration option if the sys-
tem clock source is provided by ERC or HIRC.
The SST is 1024 for HXT or LXT.
Item
0
u
u
1
SST
Power-on reset
RES or LVR reset during Normal or Slow
Mode operation
WDT time-out reset during Normal or
Slow Mode operation
WDT time-out reset during Idle or Sleep
Mode operation
can be chosen to be either 1024 or 2
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
HT45R22E
March 17, 2010
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