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BT817/8 Advanced Embedded Video Engine Datasheet

Version 1.1

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

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 BT817/8’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 BT817/8 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.

4.8.5

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 BT818 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 BT817 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);

uint16_t main = FW_RD(0) & 0xfff;

uint16_t i_set = 0x4000 | (main - 4);

uint16_t patch = main + 1;

uint16_t i_eol = FW_RD(patch);

while (num_regs--) {

uint8_t reg = *reg_value++;

uint8_t val = *reg_value++;

FW_WR(patch++, 0x8000 | val);

FW_WR(patch++, 0x8000 | reg);

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