BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 39

• Manufacturer Part Number: BS2824
• Description: Touch Key Mcu
• Manufacturer: Holtek Semiconductor Inc.

Watchdog Timer
Rev. 1.00
Watchdog Timer Operation
The Watchdog Timer, also known as the WDT, is provided to inhibit program malfunctions caused
by the program jumping to unknown locations due to certain uncontrollable external events such as
electrical noise.
The Watchdog Timer operates by providing a device reset when the Watchdog Timer counter
overflows. Note that if the Watchdog Timer function is not enabled, then any instructions related to
the Watchdog Timer will result in no operation.
Setting up the various Watchdog Timer options are controlled via the configuration options and two
internal registers WDTS and CTRL1. Enabling the Watchdog Timer can be controlled by both a
configuration option and the WDTEN bits in the CTRL1 internal register in the Data Memory.
The Watchdog Timer will be disabled if bits WDTEN3~WDTEN0 in the CTRL1 register are written
with the binary value 1010B and WDT configuration option is disable. This will be the condition
when the device is powered up. Although any other data written to WDTEN3~WDTEN0 will ensure
that the Watchdog Timer is enabled, for maximum protection it is recommended that the value
0101B is written to these bits.
The Watchdog Timer clock can emanate from three different sources, selected by configuration
option. These are LXT, f
Idle/Sleep Mode the instruction clock is stopped, therefore if the configuration options have selected
value of the Cs capacitor is equivalent to the touch pad capacitance, however the value can still be
changed to obtain the required sensitivity value. Higher Cs values will result in higher levels of
sensitivity. Recommended values for Cs are between 0pF and 10pF.
Larger touch key sizes will increase sensitivity and of course vice-versa, small electrode sizes will
decrease sensitivity.
A thinner panel will result in higher sensitivity and of course thicker panels will result in a lower
sensitivities.
The choice of the dielectric material for the panel will influence the sensitivity. Materials with higher
dielectric constants will result in higher sensitivities and lower dielectric constants will result in
lower sensitivities.
Touch key pad size
Touch key pad insulating panel thickness
Touch key pad insulating panel material
Configuration Option
Disable
Disable
SYS
Enable
/4, or LIRC. It is important to note that when the system enters the
Watchdog Timer On/Off Control
39
BS2824/BS2854/BS2868
CTRL1 Register
Disable
Enable
x
Touch Key MCU
WDT Function
OFF
ON
ON
January 27, 2010