BS85B12-3 HOLTEK [Holtek Semiconductor Inc], BS85B12-3 Datasheet - Page 49

• Manufacturer Part Number: BS85B12-3
• Description: Touch Key Flash Type 8-Bit MCU with LCD/LED Driver
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

BS85B12-3/BS85C20-3
Touch Key Flash MCU with LCD/LED Driver
Reset and Initialisation
Rev. 1.00
Reset Functions
Power-on Reset
Low Voltage Reset - LVR
A reset function is a fundamental part of any microcontroller ensuring that the device can be set to
some predetermined condition irrespective of outside parameters. The most important reset condition
is after power is first applied to the microcontroller. In this case, internal circuitry will ensure that the
microcontroller, after a short delay, will be in a well defined state and ready to execute the first
program instruction. After this power-on reset, certain important internal registers will be set to
defined states before the program commences. One of these registers is the Program Counter, which
will be reset to zero forcing the microcontroller to begin program execution from the lowest Program
Memory address.
Another type of reset is when the Watchdog Timer overflows and resets the microcontroller. All types
of reset operations result in different register conditions being setup. Another reset exists in the form of
a Low Voltage Reset, LVR, where a full reset, is implemented in situations where the power supply
voltage falls below a certain threshold.
There are several ways in which a microcontroller reset can occur, through events occurring both
internally and externally:
The most fundamental and unavoidable reset is the one that occurs after power is first applied to the
microcontroller. As well as ensuring that the Program Memory begins execution from the first
memory address, 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.
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. The LVR includes the
following specifications: For a valid LVR signal, a low voltage, i.e., a voltage in the range between
0.9V~V
state does not exceed t
specified voltage values for V
permanently on in these devices.
LVR
must exist for greater than the value t
Note: t
Note: t
LVR
, the LVR will ignore it and will not perform a reset function. One of a range of
RSTD
RSTD
Low Voltage Reset Timing Chart
is power-on delay, typical time=100ms
Power-On Reset Timing Chart
is power-on delay, typical time=100ms
LVR
can be selected using configuration options. The LVR function is
43
LVR
specified in the A.C. characteristics. If the low voltage
LVR
such as might occur when
February 1, 2011