Datasheet

STMPE811 Touchscreen controller
Doc ID 14489 Rev 6 39/65
10.2 Touch detect delay
Touch Detect Delay is an additional method used to compensate for the time it takes for the
panel voltage to be pulled high during a non-touch condition.
For example, the way it works to detect a touch:
X+ is pulled high and Y+ is driven low. After Touch Detect Delay is expired the level of X+ is
read. If no touch, X+ is high. If there is a touch, X+ is low.
If the initial voltage of X+ is low before being pulled high by the internal resistor, especially if
a filtering capacitor is connected, this time needs to be compensated. The Touch Delay
setting provides time for the voltage to be pulled high in a non-touch condition and avoids a
false report of a touch condition.
Normally the Touch Detect Delay needs to be long enough to allow the voltage to rise to V+
in a non-touch condition and this will depend on the presence of external filtering capacitors.
For more details on recommendation of Touch Detect delay register setting, refer to
STMPE811 Application Note (AN2825 ST document).