BT816Q-R datasheet(35/64 Pages) BRIDGETEK

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BT81X (815/6) Advanced Embedded Video Engine Datasheet

Version 1.0

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

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.

4.8.4

Extended Mode

Setting REG_CTOUCH_EXTENDED to 1b’0 enables extended mode. In extended mode a new set of

readout registers are available, allowing gestures and up to five touches to be read. There are two

classes of registers: control registers and status registers. Control registers are written by the MCU.

Status registers can be read out by the MCU and the BT815/6’s hardware tag system.

The five touch coordinates are packed in REG_CTOUCH_TOUCH0_XY, REG_CTOUCH_TOUCH1_XY,

REG_CTOUCH_TOUCH2_XY, REG_CTOUCH_TOUCH3_XY, REG_CTOUCH4_X and REG_CTOUCH4_Y.

Coordinates stored in these registers are signed 16-bit values, so have a range of -32768 to 32767. The

no-touch condition is indicated by x=y= -32768. These coordinates are already transformed into screen

coordinates based on the raw data read from the CTPM, using the matrix in registers

REG_CTOUCH_TRANSFORM_A-F. To obtain raw (x,y) coordinates read from CTPM, the user sets the

REG_CTOUCH_TRANSFORM_A-F registers to the identity matrix.

The BT815/6 tag mechanism is implemented by hardware, where up to 5 tags can be looked up.

4.8.5

Short-Circuit Protection

For resistive touch it is useful to protect the chip from permanent damage due to potential short-circuits

on the 4 XY lines. When a short circuit on the touch screen happens, the BT816 can detect it and stop the

touch detection operation, leaving the 4 XY pins in the high impedance state.

The short-circuit protection can be enabled/disabled by the REG_TOUCH_CONFIG.

4.8.6

Capacitive Touch Configuration

On a capacitive touch system some users may need to adjust the CTPM default values, such as the

registers affecting touch sensitivity. To do this the following sequence shall be executed once after chip

reset:

Hold the touch engine in reset (set REG_CPURESET = 2)

Write the CTPM configure register address and value to the BT815 designated memory location

Up to 10 register address/value can be added

Release the touch engine reset (set REG_CPURESET = 0)

The CTPM can be enabled in low power state when the touch function is not required by the application.

Setting the low-power bit in REG_TOUCH_CONFIG will enable the low power mode of the CTPM. When

the low-power bit is cleared, the BT815 touch engine will send a reset to the CTPM, thus re-enabling the

touch detection function.

4.8.7

Host Driven Multi-Touch

If the host MCU can provide touch inputs, it can supply them directly to the BT815 using touch host

mode. By using touch host mode, an application can choose to select a touch controller that is not in the

BT815 direct support list. For example, Touch Host mode would allow controllers to be used from other

manufacturers beyond Focaltech and Goodix.

To use the touch host mode, the host MCU shall be connected to the touch panel directly. The four touch

related pins of the BT815 can be left unconnected on the PCB. The host MCU is responsible for

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