Data Sheet

BT81X (815/6) Advanced Embedded Video Engine Datasheet

Version 1.0

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

4.8 Touch-Screen Engine

The BT815/6 touch-screen engine supports both resistive and capacitive touch panels. BT816 supports

resistive touch, while BT815 supports capacitive touch.

4.8.1 Resistive Touch Control

The resistive touch-screen consists of a touch screen engine, ADC, Axis-switches, and ADC input

multiplexer. The touch screen engine reads commands from the memory map register and generates the

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

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

Figure 4-9 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 4-17 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 in register

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.

Y+

Y-

X-

X+

BT816

Resistive Touch Screen