QT60240-ATG Datasheet, PDF (11/26 Pages) List of Unclassifed Manufacturers – 16 AND 24 KEY QMATRIX TOUCH SENSOR ICs

3.4 CHANGE Pin
Pin 2 (CHANGE) is an active-high output that can be used to
alert the host to key touches or key releases, thus reducing
the need for wasteful I²C communications. Normally, the host
can simply not bother to communicate with the device, except
when the CHANGE pin goes high.
CHANGE becomes active only when there is a change in key
state (either touch or touch release); CHANGE goes low
again only when the host performs a read from address 1, the
detect status register for all keys on Y0. CHANGE does not
self-clear; only an I²C read from location 1 will cause it to
clear.
It is important to read all three key state addresses to ensure
the host has a complete picture of which keys have changed.
In Shift Register mode the CHANGE pin does not operate
and should be left open.
Every key can be individually configured to wake a host
microcontroller upon a touch change; so, a product can wake
from sleep when any key state changes, or only when certain
desired keys change state. The configuration is set in the
Setups block (Section 6.13) on a key-by-key basis.
Key Scan
SCL
SDA
LATCH
Figure 3.2 Shift Register Cycle
Key 0 Key 1 Key 2 Key 21 Key 22 Key 23
Key 0
Key 3
Key 4
tSCL
tSCH
tSDA-SCL
Key 23
tLATCH
lQ
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QT60240-ISG R8.06/0906