Datasheet

STMPE811 Touchscreen controller
Doc ID 14489 Rev 6 33/65
10 Touchscreen controller
The STMPE811 is integrated with a hard-wired touchscreen controller for 4-wire resistive
type touchscreen. The touchscreen controller is able to operate completely autonomously,
and interrupt the connected CPU only when a pre-defined event occurs.
Figure 9. Touchscreen controller block diagram
10.1 Driver and switch control unit
The driver and switch control unit allows coordination of the ADC and the MUX/switch. With
the coordination of this unit, a stream of data is produced at a selected frequency.
The touchscreen drivers can be configured with 2 current ratings: 20 mA or 50 mA. In the
case where multiple touch-down on the screen is causing a short, the current from the driver
is limited to these values. Tolerance of these current setting is +/- 25%.
Movement tracking
The "Tracking Index" in the TSC_CTRL register specifies a value, which determines the
distance between the current touch position and the previous touch position. If the distance
is shorter than the tracking index, it is discarded.
The tracking is calculated by summation of the horizontal and vertical movement. Movement
is only reported if:
(Current X - Previously Reported X) + (Current Y - Previously Reported Y) > Tracking Index
If pressure reporting is enabled (X/Y/Z), an increase in pressure override the movement
tracking and report the new data set, even if X/Y is within the previous tracking index. This is
to ensure that a slow touch is not discarded.
If pressure data is not used, select X/Y mode in touchscreen data acquisition. (Opmode field
in TSCControl register).
s
Movement
&
window tracking
10/12 bit
ADC
Switch
&
drivers
Driver
&
switch control
FIFO
&
interrupt control
FIFO