BS2824 Holtek Semiconductor Inc., BS2824 Datasheet - Page 37

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

Rev. 1.00
The MCU then changes its I/O pin to an input. Now the touch switch circuitry will then pull the SCD
line low, then high, the timings are given by the synchronise period. This allows the MCU to
synchronise itself for the data transfer.
The touch switch circuitry will then transmit its key status, given as D0~Dn. For the BS2824 and
BS2854 the data format is D0~D3. For the BS2868 the data format is D0~D7.
The MCU can then read the key status taking care to read the data in the centre of the transmitted
data pulse. After the last data bit is transferred the touch key circuitry will return the SCD pin to
an input state.The timings associated with the above protocol can be described in multiples of the
SCD clock periods. The SCD clock period is about about 76 s.
A certain time is required for the to transmit three or more pulses to inform the touch key circuitry
that it desires to read the key status. After this time has elapsed the device will then transmit the data
bits, D0~Dn.
Each bit of transmitted data corresponds directly to a touch input key. Therefore the status of touch
key Key0 is represented by D0, Key1 by D1 and so on. A low bit means that a touch has been
detected, a high bit means no touch has been detected.
The desired Operating Mode to be setup depends upon the number of pulses received within a
time period, 4 t
and the SCD line returns high, the device will return to normal operation. Note that these pulses must
be transmitted within 4 t
Sending commands to the touch circuitry
The MCU can send commands along the SCD line to setup the touch keys in different Operating
Modes. To do this an I/O pin takes control of the SCD line, first forcing it low and holding it low
for a time of greater than 8 t
and enable them to receive commands from the MCU.
SCD
, as shown in the table. After the programming clock cycles have been transmitted
SCD
.
BS2824/BS2854
SCD
Key0
Key1
Keyn
Pin
:
:
BS2868
Device
cycles. This action will temporarily disable the touch key circuits
Key Status Read Total Time
SCD Device Setup
37
BS2824/BS2854/BS2868
Data Bit
D0
D1
Dn
:
:
22 t
38 t
Time
Touch Key MCU
1: Key Off
0: Key On
Dn Value
SCD
SCD
January 27, 2010