HT46R94 Datasheet, PDF (38/62 Pages) Holtek Semiconductor Inc – A/D Type 8-Bit MCU with 16
16 High Current LED Driver

HT46R94
· Low Voltage Reset - LVR
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_LVR such as might occur when
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_LVR must exist for a time greater than that spec-
ified by t_LVR in the A.C. characteristics. If the low sup-
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_LVR value can be se-
lected via configuration options.
LV R
tR S T D
S S T T im e - o u t
In te rn a l R e s e t
Low Voltage Reset Timing Chart
· 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 ²1².
W D T T im e - o u t
tR S T D
S S T T im e - o u t
In te rn a l R e s e t
WDT Time-out Reset during Normal Operation
Timing Chart
· _{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
²0² and the TO flag will be set to ²1². Refer to the A.C.
Characteristics for t_SST details.
W D T T im e - o u t
tS S T
S S T T im e - o u t
WDT Time-out Reset during Power Down
Timing Chart
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:
TO PDF
RESET Conditions
0 0 RES reset during power-on
u u RES or LVR reset during normal operation
1 u WDT time-out reset during normal operation
1 1 WDT time-out reset during Power Down
Note: ²u² 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.
Item
Condition After RESET
Program Counter Reset to zero
Interrupts
All interrupts will be disabled
WDT
Clear after reset, WDT begins
counting
Timer/Event
Counter
Timer Counter will be turned off
Prescaler
The Timer Counter Prescaler will
be cleared
Input/Output Ports I/O ports will be setup as inputs
Stack Pointer
Stack Pointer will point to the top
of the stack
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
accompanying table describes how each type of reset
affects each of the microcontroller internal registers.
Rev. 1.10
38
November 5, 2008