BS801B HOLTEK [Holtek Semiconductor Inc], BS801B Datasheet - Page 7

• Manufacturer Part Number: BS801B
• Description: Touch Key
• Manufacturer: HOLTEK [Holtek Semiconductor Inc]

lows three functions to be implemented, two are initiated
by the external MCU and one by the BS80xB.
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 MCU to transmit three
or more pulses to inform the device that it desires to
Rev. 1.00
Wake-up or Interrupt
MCU
Read Touch Key
Status
Send command to
BS804B/BS808B
BS804B/BS808B Wakes-up or Interrupts MCU
When any of the touch keys change state, a pulse will
be generated by the BS804B/BS808B 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
MCU reads the touch key status
The MCU can send a command to the BS804B/
BS808B device to request the touch key status. The
protocol for reading the touch key status is as follows:
SCD
SCD Command
The external MCU takes control of the SCD line and
first sends three rising edge pulses or more to the
BS804B/BS808B within a time of about 152 s.
The MCU then changes its I/O pin to an input.
The BS804B/BS808B device will then pull the SCD
line low, then high, the timings are given by syn-
chronise period. This allows the MCU to synchro-
nise itself for the data transfer.
The BS804B/BS808B device will then transmit its
key status, given by D0~Dn
The MCU can then read the key status taking care
to read the data in the centre of the transmitted data
pulse.
Af t e r th e l as t data b i t is trans fe rr ed the
BS804B/BS808B device will return its SCD pin to
an input state.
/2 period where t
For the BS804B, the data format is D0~D3.
For the BS808B, the data format is D0~D7.
Wake-up/Interrupt Pulse to MCU
SCD Function Summary
SCD
BS804B/BS808B
Step1: MCU send command
MCU
Step2: MCU read key status
BS804B/BS808B
MCU
is about 76 s.
BS804B/BS808B
BS804B/BS808B
Direction
MCU
MCU
7
read the key status. After this time has elapsed the de-
vice 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.
MCU sends commands to BS804B/BS808B device
The MCU can send commands along the SCD line to
setup the device in different Operating Modes. To do
this the externally connected MCU takes control of the
SCD line, first forcing it low and holding it low for a
time of greater than 8 t
porarily disable the device and enable it to receive the
command from the MCU. Any command sent to the
device from the MCU will override the original power
on configuration setup.
The desired Operating Mode to be setup depends
upon the number of pulses received by BS804B/
BS808B within a time period, 4 t
table. After the programming clock cycles have been
transmitted and the SCD line returns high, the device
will return to normal operation.
Clock Pulses
0~2
3~6
7~10
11~14
>15
Key0
Key1
Keyn
BS804B and BS808B SCD Commands
Pin
:
:
BS804B
BS808B
Device
Key Status Read Total Time
BS801B/02B/04B/06B/08B
SCD Device Setup
Set by external pin
One-key wake-up
For test purposes
Any-Key wake-up
Always normal operation
Data Bit
SCD
D0
D1
Dn
:
:
cycles. This action will tem-
Operating Mode
SCD
22 t
38 t
, as shown in the
Time
1: Key Off
0: Key On
Dn Value
SCD
SCD
July 7, 2009