HT82B40A HOLTEK [Holtek Semiconductor Inc], HT82B40A Datasheet - Page 24

• Manufacturer Part Number: HT82B40A
• Description: I/O MCU with USB Interface
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

Rev. 1.10
For most applications a resistor connected between
VDD and the RES pin and a capacitor connected be-
tween VSS and the RES pin will provide a suitable ex-
ternal reset circuit. Any wiring connected to the RES
pin should be kept as short as possible to minimise
any stray noise interference.
For applications that operate within an environment
where more noise is present the Enhanced Reset Cir-
cuit shown is recommended.
More information regarding external reset circuits is
located in Application Note HA0075E on the Holtek
website.
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.
Power-On Reset Timing Chart
RES Reset Timing Chart
Enhanced Reset Circuit
Basic Reset Circuit
24
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 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.
WDT Time-out Reset during Power Down
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-
HT82B40R/HT82B40A
Timing Chart
Timing Chart
SST
LVR
details.
LVR
such as might occur when
LVR
September 4, 2009
value can be se-