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BT81X (815/6) Advanced Embedded Video Engine Datasheet

Version 1.0

Document No.: BRT_000220 Clearance No.: BRT#126

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.

4.8.2

Capacitive Touch Control

The Capacitive Touch Screen Engine (CTSE) of the BT815 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 BT815/6 will read the touch data through

I2C. Up to 5 touches can be reported and stored in BT815 registers.

The BT815 CTSE supports Focaltech and Goodix touch controllers, as well as touch host mode (refer to

section 4.8.7). For a supported CTPM list please refer to AN_336 FT8xx - Selecting an LCD Display.

The BT815 uses the I2C address value in the REG_TOUCH_CONFIG register to differentiate Focaltech or

Goodix touch controllers. For Focaltech IC the I2C address must be set as 0x38-0x3F (example:

REG_TOUCH_CONFIG = 0x0380), while for Goodix IC the I2C address must be set as 0x5D (example:

REG_TOUCH_CONFIG = 0x05D0).

Figure 4-10 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 BT815 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 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).

4.8.3

Compatibility Mode

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

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

SCL

RSTN

SDA

INTN

BT815

CTP_SCL

CTP_SDA

CTP_INT_N

CTP_RST_N

Capacitive Touch

Panel Module

VCCIO2

(1.8-3.3V)

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