CTPM Application Note
3
FocalTech Systems, Ltd. Confidential
Read X bytes from I
2
C Slave
S
A
6
A
5
A
4
A
3
A
2
A
1
A
0
R
W
A
D
6
D
5
D
4
D
3
D
2
D
1
D
0
A
D
7
…
D
6
D
5
D
4
D
3
D
2
D
1
D
0
A
D
7
P
Slave Addr Data [N] Data [X+N-1]
START
Read
ACK
ACK
ACK
STOP
Note: In the I2C Read/Write mode, the Data Address should not be more than 0xFF, it will stays at 0xFF when
reaching 0xFF.
1.3 Interrupt signal from CTPM to Host
As for standard CTPM, host need to use both interrupt control signal and serial data interface to get the touch
data. There are two kind of method to use interrupt: interrupt trigger and interrupt query.
Note: In Interrupt query mode, To avoid missing touch data, the sampling rate should be bigger than the
report rate.
Here is the timing to get touch data.
Data Packet
0
Data Packet
1
……
Data Packet
N
Blank
Blank
/INT
Touch Start Touch End
Serial
Data
Figure 1-2 Interrupt query mode
Data Packet
0
Data Packet
1
……
Data Packet
N
Blank
Blank
/INT
Touch Start Touch End
Serial
Data
Figure 1-3 Interrupt trigger mode
Host use general I2C protocol to read the touch data or the information from CTPM . CTPM will send host a
interrupt signal when there is a valid touch. Then host can use the serial data interface to get the touch data. If
there is no valid touch detected, the /INT will not be pulled up, the host do not need to read the touch data.
NOTE: “valid touch” may have different definition in various systems. For example, in some systems, the valid
touch is defined as there is one more valid touch point. But in some other systems, the valid touch is defined as
one more valid touch with valid gestures. In usual, /INT will be pulled up when there is a valid touch point, and
to be low when a touch finishes.
As for interrupt trigger mode, /INT signal will be low if there is no touch detected. But for per update of valid
touch data, CTPM will produce a valid pulse for /INT signal, host can read the touch data periodically
according to the frequency of this pulse. In this mode, the pulse frequency is the touch data update frequency.
.
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