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BT817/8 Advanced Embedded Video Engine Datasheet

Version 1.1

Document No.: BRT_000302 Clearance No.: BRT#154

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

other touch controller IC, consult Bridgetek.

The BT817 uses the I2C address value in the REG_TOUCH_CONFIG register to differentiate

Focaltech/Hycontek and Goodix touch controllers. For Focaltech/Hycontek 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). The touch engine requires a reset if

changing I2C address from default value, as shown below:

Write REG_CPURESET = 2

Write REG_TOUCH_CONFIG = 0x05D0

//For Goodix touch controller

Write REG_CPURESET = 0

The BT817 supports I2C clock stretch. This is particularly useful for supporting Hycontek touch IC.

Figure 4-8 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 4-20 Capacitive Touch Controller Operating Mode

The BT817 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). These touch values are

transformed into screen coordinates using the matrix in registers REG_CTOUCH_TRANSFORM_A-F. The

post-transform coordinates are available in register 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

BT817

CTP_SCL

CTP_SDA

CTP_INT_N

CTP_RST_N

Capacitive Touch

Panel Module

VCCIO2

(1.8-3.3V)

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