ht82j31a Holtek Semiconductor Inc., ht82j31a Datasheet - Page 22

• Manufacturer Part Number: ht82j31a
• Description: 16 Channel A/d Mcu With Spi Interface
• Manufacturer: Holtek Semiconductor Inc.

Rev. 1.00
then any external components connected to the exter-
nal reset pin will have no effect and only the internal
RC circuit will provide the reset function.
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. Note that as the external reset pin
is also pin-shared with PA7, if it is to be used as a reset
pin, the correct reset configuration option must be se-
lected.
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 .
WDT Time-out Reset during Normal Operation
LVR
Low Voltage Reset Timing Chart
LVR
must exist for a time greater than that spec-
in the A.C. characteristics. If the low sup-
RES Reset Timing Chart
Timing Chart
LVR
LVR
such as might occur when
LVR
value can be se-
22
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
the microcontroller internal registers.
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
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
0 and the TO flag will be set to 1 . Refer to the A.C.
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
SST
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
details.
Condition After RESET
September 19, 2007
HT82J31A