HT37B90/HT37B70/HT37B50/HT37B30
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:
RES Reset Timing Chart
TO PDF
RESET Conditions
RES reset during power-on
·
Low Voltage Reset - LVR
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 and
The VLVR can select as 3.0V or 2.4V. If the supply
voltage of the device drops to within a range of
0.9V~VLVR such as might occur when changing the
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~VLVR must exist for
greater than the value tLVR specified in the A.C. char-
acteristics. If the low voltage state does not exceed
1ms, the LVR will ignore it and will not perform a reset
function.
0
u
0
1
1
0
u
1
u
1
RES or LVR reset during normal operation
RES Wake-up HALT
WDT time-out reset during normal operation
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
WDT
All interrupts will be disabled
Clear after reset, WDT begins
counting
Low Voltage Reset Timing Chart
Timer/Event
Counter
Timer Counter will be turned off
·
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.
The Timer Counter Prescaler will
be cleared
Prescaler
Input/Output Ports I/O ports will be setup as inputs
Stack Pointer will point to the top
Stack Pointer
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
following table describes how each type of reset affects
each of the microcontroller internal registers.
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 tSST details.
WDT Time-out Reset during Power Down
Timing Chart
Rev. 1.00
34
June 22, 2017
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
