STMPE812A datasheet(39/53 Pages) STMICROELECTRONICS

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STMPE812A

Touchscreen controller

Doc ID 18225 Rev 4

39/53

11.4

Programming model

Below are steps to configure the Touchscreen controller in 3 different acquisition modes.

A. Autonomous touchscreen controller, 100 Hz, lowest power possible

Initialize the touchscreen controller (choose ACQ_Mode ‘00’ - data acquisition timed by

internal timer)

Initialize interrupt (with TSC_Data enabled, normal interrupt mode)

Wait for interrupt

On interrupt: Read interrupt status (this clears the set bits too)

If data is available, read data.

Note:

If one set of data is available in buffer, and not accessed by the I2C host, yet the sampling

timer is up for the next data, the STMPE812A samples the next data as scheduled.

If old data is still NOT accessed when new data is ready to be written to the buffer, it is over-

written.

If old data is IN PROGRESS of being accessed, new data is DISCARDED.

If I2C host accessed PART OF the data, and moved on to read ANY OTHER REGISTER

LOCATION, the existing data is CONSIDERED READ, and new data ready to be written into

buffer

B. Non-autonomous touchscreen controller style-interrupt, 100Hz, lowest

power possible:

Initialize TSC (Choose ACQ_Mode ‘01’ - Data acquisition triggered by a write to “ACQ”

bit)

Initialize Interrupt (With TSC_Data, TSC_Touch enabled, PEN_DOWN interrupt mode)

Wait for Interrupt

On Interrupt: Read Interrupt Status (this clears the set bits too)

If PEN_DOWN, start SYSTEM_TIMER (10 ms typically)

On TIMEOUT, write ACQ bit to start acquisition

Poll interrupt status register or ACQ bit to check for acquisition status

ON issuing ACQ, 812 may assume that data in buffer is already accessed by I2C host,

and reset the relevant pointers.

C. Host-controlled sampling rate (lowest bus utilization)

Initialize TSC (choose ACQ_Mode ‘10’ - Data acquisition using host-controlled

sampling rate control)

Initialize interrupt (with TSC_Data, TSC_Touch enabled, PEN_DOWN interrupt mode)

Wait for Interrupt

On interrupt: Read Interrupt Status (this clears the set bits too)

If PEN_DOWN, start SYSTEM_TIMER (10 ms typically)

On TIMEOUT, read data

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