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FT801 Embedded Video Engine Datasheet

Version 1.3

Document Reference No.: BRT_000001

Clearance No.: BRT#003

4.7 Touch-Screen Engine

The Capacitive Touch Screen Engine (CTSE) of FT801 communicates with external capacitive touch panel

module (CTPM) through I2C interface. The CTPM will assert its interrupt line when there is a touch

detected. Upon detecting CTP_INT_N line active, the FT801 will read the touch data through I2C. Up to 5

touches can be reported and stored in FT801 registers. FT801 currently supports CTPM with FT5x06 or

IQS5xx drive chip.

Figure 4-7 Touch screen connection

The host controls the CTSE operation mode by writing the REG_CTOUCH_MODE.

REG_CTOUCH_MODE Mode

Description

OFF

Acquisition stopped

ONE-SHOT

Perform acquisition once every time MPU write '1' to

REG_CTOUCH_MODE.

Reserved

CONTINUOUS

Perform acquisition continuously at the reporting rate of the

connected CTPM.

Table 4-14 Touch Controller Operating Mode

The FT801 CTSE supports compatibility mode and extended mode. By default the CTSE runs in

compatibility mode where the touch system provides an interface very similar to the FT800’s. In this

mode the same application code can run on FT800 and FT801 without alteration. In extended mode, the

touch register meanings are modified, and a second set of registers are exposed. These allow multi-touch

detection.

4.7.1 Compatibility mode

The CTSE reads the X and Y coordinates from CTPM and writes to register REG_CTOUCH_RAW_XY. If the

touch screen is not being pressed, both registers read 65535 (FFFFh).

These touch values are transformed into screen coordinates using the matrix in registers

REG_CTOUCH_TRANSFORM_A-F.

The

post-transform

coordinates

are

available

REG_CTOUCH_SCREEN_XY. If the touch screen is not being pressed, both registers read -32768 (8000h).

The values for REG_CTOUCH_TRANSFORM_A-F may be computed using an on-screen calibration process.

If the screen is being touched, the screen coordinates are looked up in the screen's tag buffer, delivering

a final 8-bit tag value, in REG_TOUCH_TAG. Because the tag lookup takes a full frame, and touch

coordinates change continuously, the original (x; y) used for the tag lookup is also available in

REG_TOUCH_TAG_XY.

SCL

RSTN

SDA

INTN

FT801

CTP_SCL

CTP_SDA

CTP_INT_N

CTP_RST_N

Capacitive Touch

Panel Module

3.3V

GND

4.7K

10K

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