ht82a836r Holtek Semiconductor Inc., ht82a836r Datasheet - Page 30

• Manufacturer Part Number: ht82a836r
• Description: Usb Audio Mcu
• Manufacturer: Holtek Semiconductor Inc.

Rev. 1.00
dress, a power-on reset also ensures that certain
other registers are preset to known conditions. All the
I/O port and port control registers will power up in a
high condition ensuring that all pins will be first set to
inputs.
Although the microcontroller has an internal RC reset
function, if the VDD power supply rise time is not fast
enough or does not stabilise quickly at power-on, the
internal reset function may be incapable of providing
proper reset operation. For this reason it is recom-
mended that an external RC network is connected to
the RESET pin, whose additional time delay will en-
sure that the RESET pin remains low for an extended
period to allow the power supply to stabilise. During
t h i s t i m e d e l a y, n o r m a l o p e r a t i o n o f t h e
microcontroller will be inhibited. After the RESET line
reaches a certain voltage value, the reset delay time
t
which the microcontroller will begin normal operation.
The abbreviation SST in the figures stands for System
Start-up Timer.
For most applications a resistor connected between
VDD and the RESET pin and a capacitor connected
between VSS and the RESET pin will provide a suit-
able external reset circuit. Any wiring connected to the
RESET pin should be kept as short as possible to min-
imize any stray noise interference.
For applications that operate within an environment
where more noise is present the Enhanced Reset Cir-
cuit shown is recommended.
RES Pin Reset
This type of reset occurs when the microcontroller is
already running and the RESET 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
RSTD
is invoked to provide an extra delay time after
Power-On Reset Timing Chart
Enhanced Reset Circuit
Basic Reset Circuit
30
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, which is selected via a configuration option. If the
supply voltage of the device drops to within a range of
0.9V~V
battery, the LVR will automatically reset the device in-
ternally. The LVR includes the following specifica-
tions: For a valid LVR signal, a low voltage, i.e., a
voltage in the range between 0.9V~V
greater than the value t
acteristics. If the low 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.
WDT Time-out Reset during Power Down
LVR
Low Voltage Reset Timing Chart
such as might occur when changing the
RES Reset Timing Chart
Timing Chart
Timing Chart
SST
LVR
details.
LVR
specified in the A.C. char-
HT82A836R
LVR
March 20, 2008
must exist for