Rainbow Electronics AT42QT1110-AZ - Manual (Page 21)

21
9570H–AT42–02/10
AT42QT1110-MZ/AT42QT1110-AZ
4.11.2 Burst Length Limitations
The maximum burst length is 2048 pulses. The recommended design is to use a capacitor that
gives a signal of <1000 pulses.
The number of pulses in the burst can be obtained by reading the key signal (that is, the number
of pulses to complete measurement of the key’s signal) over the SPI interface (see
Section 6.8
on page 26 ). Alternatively, a scope can be used to measure the entire burst, and then the burst
length divided by the time for a single pulse.
Note that the keys are independent of each other. It is therefore possible, for example, to have a
signal of 100 on one key and a signal of 1000 on another.
4.11.3 Adjacent Key Suppression Technology
The device includes Atmel’s patented Adjacent Key Suppression (AKS) technology to allow the
use of tightly spaced keys on a keypad with no loss of selectability by the user.
AKS is enabled or disabled for each key individually; only one key out of those enabled for AKS
may be reported as touched at any one time. The first key touched dominates and stays in
detect until it is released, even if another stronger key is reported. Once it is released, the next
strongest key is reported. If two keys are simultaneously detected, the strongest key is reported,
allowing a user to slide a finger across multiple keys with only the dominant key reporting touch.
Each key can be enabled for AKS processing via the AKS mask (see Section 7.11 on page 33 ).
Keys outside the group of enabled keys may be in detect simultaneously.