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BT817/8 Advanced Embedded Video Engine Datasheet

Version 1.1

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

the required control signals to the axis-switches and inputs mux and ADC. The ADC data is acquired,

processed and updated in the respective register for the MPU/MCU to read.

Figure 4-7 Resistive Touch Screen Connection

The host controls the TOUCH SCREEN ENGINE operation mode by writing the REG_TOUCH_MODE.

REG_TOUCH_MODE

Mode

Description

OFF

Acquisition stopped, only touch detection interrupt is still

valid.

ONE-SHOT

Perform acquisition once every time the MPU writes '1' to

REG_TOUCH_MODE.

FRAME-SYNC

Perform acquisition for every frame sync (~60 data

acquisition/second.

CONTINUOUS

Perform acquisition continuously at approximately 1000

data acquisition / second.

Table 4-19 Resistive Touch Controller Operating Mode

The Touch Screen Engine captures the raw X and Y coordinate and writes to register

REG_TOUCH_RAW XY. The range of these values is 0-1023. 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_TOUCH_TRANSFORM_A-F.

The

post-transform

coordinates

are

available

REG_TOUCH_SCREEN_XY. If the touch screen is not being pressed, both registers read -32768

(8000h).

The values for REG TOUCH 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.

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_RZTHRESH (valid in touch continuous mode, frame mode and one-shot

mode) 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 BT817 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 BT817/8 will read the touch data

through I2C. Up to 5 touches can be reported and stored in BT817 registers. The BT817 built-in ROM

code supports Focaltech, Hycontek and Goodix touch controllers, as well as touch host mode (refer to

Y+

Y-

X-

X+

BT818

Resistive Touch Screen

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