STMPE811_09 datasheet(32/64 Pages) STMICROELECTRONICS

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Touch screen controller

STMPE811

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Doc ID 14489 Rev 2

Touch screen controller

The STMPE811 is integrated with a hard-wired touch screen controller for 4-wire resistive

type touch screen. The touch screen controller is able to operate completely autonomously,

and will interrupt the connected CPU only when a pre-defined event occurs.

Figure 9.

Touch screen 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 touch screen 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 will 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 will not be discarded.

If pressure data is not used, select X/Y mode in touch screen data acquisition. (Opmode

field in TSCControl register).

Movement

window tracking

10/12 bit

ADC

Switch

drivers

Driver

switch control

FIFO

interrupt control

FIFO

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