STMPE812ABJR datasheet(32/53 Pages) STMICROELECTRONICS

32 / 53 page

Touchscreen controller

STMPE812A

32/53

Doc ID 18225 Rev 4

11.1

Touchscreen controller detection sequence

Following is the sequence of detection in the STMPE812A touchscreen controller for X, Y

and Z:

Touch detect

Drive Y

Wait for settling time

Measure Y

Stop drive

Drive Z

Wait for settling time

Measure Z

Stop drive

10. Drive X

11. Wait for settling time

12. Measure X

13. Stop drive

14. Touch detect

11.2

3 modes of acquisition

Data acquisition timed by internal timer:

The host system selects a “sampling period” with, based on internal timer, the touchscreen

controller takes a complete set of samples on every period. The host system may choose to

read the data by:

–

Waiting for the INT

–

Polling for INT_STATUS register for TOUCH DATA

–

Reading the TSC_DATA at approximately the same timing. (Use “Data Valid Status

Read” option in this mode)

Data acquisition triggered by a write to “ACQ” bit:

As and when sampling is desired, host writes to the ACQ bit and:

–

Poll the ACQ to wait for completion

–

Wait for INT for Touch Data access

–

Poll the FIFO after approximate time required for sampling. (Use “Data Valid

Status Read” option in this mode)

Data acquisition using host-controlled sampling rate control

The host sets the internal timer for the desired data-rate. On staring the touchscreen

controller in this mode, a complete set of sample is taken immediately. The touchscreen

controller enters in hibernate mode (clock is turned OFF, only monitors the PEN-DOWN

status). When system host reads the Touch Data available in FIFO, another set of data is

taken immediately.

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