BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 36

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

BS2824/BS2854/BS2868
Touch Key MCU
Rev. 1.00
Operation Modes
Serial Interface - SCD
The touch keys have two modes of operation, the Standby Mode and the Normal Mode. After the
device is powered up it will automatically enter the Standby Mode to conserve power. The devices
can then be directly woken up by a One-key Wake-up using Key0. However if the devices are setup
by the microcontroller to be in the Any Key Wake-up mode, they can be woken up by touching any
key.
The advantage of choosing the One-key wake-up option is that it consumes less power than the
Any-key wake-up when in the Standby Mode.
When in the Standby Mode, after a relevant Keyn wake-up detection has been made, the
device will switch to the Normal Mode and await subsequent switch detections on all their Keyn
pins. It will remain in the Normal Mode for about 20 seconds and if no further detections are made
during this time will return to the Standby Mode.
Both devices are equipped with a single line serial interface on the SCD pin, allowing for easy
interfacing to the MCU circuitry. By connecting this SCD pin to one of the I/O pins, usually the INT
or TC0 or TC1 pin, then by using this interface, the MCU can serially read the status of the touch
keys at any time. The Serial interface also allows the MCU to send commands to the touch keys. The
serial interface allows three functions to be implemented, two are initiated by the MCU circuitry and
one by the touch key circuitry.
When any of the touch keys change state a pulse will be generated on the SCD pin which can be
used to wake-up or interrupt the internal MCU. To do this the SCD pin must be externally
connected to the INT, TC0, TC1 or an I/O pin. More information on this wake-up method is
provided in the Microcontroller Operating Mode section of the datasheet.
Commands can be sent to the touch key circuitry to request the touch key status. The protocol for
reading the touch key status is as follows:
The MCU first sets its I/O pin to an output and sends three or more rising edge pulses to the SCD
pin within a time of about 152 s.
Touch Keys Wake-up or Interrupt the MCU
MCU reads the touch key status
Wake-up or Interrupt MCU
Read Touch Key Status
Send command to Touch Key
SCD Command
Serial Interface Operating Mode
SCD Function Summary
Touch Key
Step1: MCU send command MCU
Step2: MCU read key status Touch Key
MCU
36
Touch Key
MCU
Direction
Touch Key
January 27, 2010
MCU