BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 35

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

Touch Key Wake-up
Rev. 1.00
Touch Key Function
Touch Key Operation
When the touch key circuits are in the standby state they will be woken up again when a touch action
occurs on their key sense pads. This will however not automatically wake-up the the
microcontroller. However when a touch action wakes up the touch key circuits, a low pulse will be
generated on the SCD pin line which can be connected to the external interrupt pin, INT, or timer
input pin, TC0 or TC1, to wake up the microcontroller. If the timer pin is used to wake up the
microcontroller then the appropriate timer must be setup in the event counting mode and preloaded
with a value of FEH. Then when a pulse is received on its timer input pin the counter will overflow
and generate an interrupt and corresponding wake up signal. The pulse generated by SCD is equal to
a t
The devices contain 4 or 8 touch key inputs which can detect human body contact using external
touch pads. The high level of integration enable touch key applications to be implemented with a
minimum number of external components.
The touch key circuitry contains a single line serial interface to allow easy communication with a
microcontroller I/O pin for touch key setup and for touch key monitoring purposes. Special internal
circuitry is also employed to ensure excellent power noise rejection to reduce the possibility of
false detections, increasing the touch switch application reliability under adverse environmental
conditions. With auto-calibration, low standby current and a choice of wake-up features, this range
of touch key devices provides a simple and effective means of implementing touch switches in a
wide variety of applications.
SCD
/2 period where tSCD is about 76 s.
35
Operating Flow
BS2824/BS2854/BS2868
Touch Key MCU
January 27, 2010