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BT817A Automotive Advanced Video Engine Datasheet

Version 1.0

Document No.: BRT_000251 Clearance No.: BRT#194

The BT817A CTSE supports compatibility mode and extended mode. By default, the CTSE runs in

compatibility mode. 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).

4.8.2 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.

4.8.3 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 BT817A’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 BT817A tag mechanism is implemented by hardware, where up to 5 tags can be looked up.

In touch extended mode, the INT_TOUCH bit in REG_INT_FLAG register will not be set upon touch

down event. It is recommended to use INT_CONV_COMPLETE bit instead.

4.8.4 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 BT817A designated memory

location

Up to 10 register address/value can be added

Release the touch engine reset (set REG_CPURESET = 0)

Sample codes are listed below for configuring Focaltech touch controller:

#define FW_RD(a)

VC.rd16(RAM_JTBOOT + 2 * (a))

#define FW_WR(a, v) VC.wr16(RAM_JTBOOT + 2 * (a), (v))

void init_custom_touch(size_t num_regs, uint8_t *reg_value)

{

while (VC.rd(REG_CPURESET) != 0)

;

VC.wr(REG_CPURESET, 2);

BT817AQ-R Datasheet(PDF) 33 Page - Bridgetek Pte Ltd.

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