BS801C/02C/04C/06C/08C
Touch Key Outputs
All Kout pins have NMOS structures to allow easy inter-
facing to external devices with different operating volt-
ages. The BS801C, BS802 and BS804C devices can
have their outputs configured to operate with either
Level-Hold or Toggle type. The output type is deter-
mined by the status of the LHF pin which is read during
power-on. The logic level on this pin must not be
changed after power on. Internal circuitry ensures that
the internal pull-high resistor on the LHF pin will not
consume current. The BS806C and BS808C only have
Level-Hold output types.
Part No.
BS801C
BS802C
BS804C
BS806C
BS808C
LHF
Open
Low
¾
Kout Type
Level-Hold
Toggle
Level-Hold
mands to the touch key device. The serial interface al-
lows three functions to be implemented, two are initiated
by the external MCU and one by the BS80xC.
SCD Command
Wake-up or Interrupt
MCU
Read Touch Key
Status
Send command to
BS804C/BS808C
Direction
BS804C/BS808C
®
MCU
Step1: MCU send command
MCU
®
BS804C/BS808C
Step2: MCU read key status
BS804C/BS808C
®
MCU
MCU
®
BS804C/BS808C
SCD Function Summary
·
BS804C/BS808C Wakes-up or Interrupts MCU
Serial Interface
-
SCD
Both the BS804C and BS808C are equipped with a sin-
gle line serial interface on the SCD pin, allowing for easy
interfacing to an external MCU.
This single line interface allows communication in both
directions between the touch key device and the external
MCU. Using this interface, the external MCU can serially
read the status of the touch keys at any time. The Serial
interface also allows the external MCU to send com-
When any of the touch keys change state, a pulse will
be generated by the BS804C/BS808C device which
can be used to wake up or to interrupt an external
MCU. The MCU must ensure that its pin connected to
the SCD pin is setup as an input to receive this pulse.
The pulse width generated by the device is equal to a
t
SCD
/2 period where t
SCD
is about 76ms.
t
S
O /P
C D
/2
IN T
o r
I/O
B S 8 0 4 C
B S 8 0 8 C
S C D
I/P
M C U
Wake-up/Interrupt Pulse to MCU
P o w e r O n
O n e -K e y S ta te
Y
O K W
O p e n ?
O K W
N
lo w
A n y -K e y S ta te
K e y 0 O n ?
N
R e tu rn to
O n e -K e y S ta te
A n y -K e y
O n ?
Y
E n a b le K e y n O u tp u t
N
E n a b le K e y 0 O u tp u t
Y
A n y -K e y o n
w ith in 2 0 s e c . ?
N
Y
E n a b le K e y n O u tp u t
BS804C, BS806C and BS808C Operating Flow
Rev. 1.00
6
December 2, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
