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FT81X Embedded Video Engine Datasheet

Version 1.4

Document No.: BRT_000002 Clearance No.: BRT#004

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.

Screen touch pressure is available in REG_TOUCH_RZ. The value is relative to the resistance of the touch

contact, a lower value indicates more pressure. The register defaults to 32767 when touch is not

detected. The REG_TOUCH_THRESHOLD can be set to accept a touch only when the force threshold is

exceeded.

4.7.2

Capacitive Touch Control

The Capacitive Touch Screen Engine (CTSE) of the FT81x communicates with the external capacitive

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

a touch detected. Upon detecting CTP_INT_N line active, the FT81x will read the touch data through I2C.

Up to 5 touches can be reported and stored in FT81x registers.

For a supported CTPM list please consult FTDI website.

Figure 4-9 Touch screen connection

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

REG_CTOUCH_MODE

Mode

Description

OFF

Acquisition stopped

1-2

Reserved

CONTINUOUS Perform acquisition continuously at the reporting rate of the

connected CTPM.

Table 4-18 Capacitive Touch Controller Operating Mode

The FT81x 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 resistive touch

engine. In this mode the same application code can run on FT810/FT812 and FT811/FT813 without

alteration. In extended mode, the touch register meanings are modified, and a second set of registers are

exposed. These allow multi-touch detection (up to 5 touches).

SCL

RSTN

SDA

INTN

FT811/

FT813

CTP_SCL

CTP_SDA

CTP_INT_N

CTP_RST_N

Capacitive Touch

Panel Module

VCCIO2

(1.8-3.3V)

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