Data Sheet

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BT81X (815/6) Advanced Embedded Video Engine Datasheet
Version 1.0
Document No.: BRT_000220 Clearance No.: BRT#126
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_THRESHOLD 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 BT815 communicates with the external capacitive
touch panel module (CTPM) through an I
2
C interface. The CTPM will assert its interrupt line when there is
a touch detected. Upon detecting CTP_INT_N line active, the BT815/6 will read the touch data through
I
2
C. Up to 5 touches can be reported and stored in BT815 registers.
The BT815 CTSE supports Focaltech and Goodix touch controllers, as well as touch host mode (refer to
section 4.8.7). For a supported CTPM list please refer to AN_336 FT8xx - Selecting an LCD Display.
The BT815 uses the I2C address value in the REG_TOUCH_CONFIG register to differentiate Focaltech or
Goodix touch controllers. For Focaltech IC the I2C address must be set as 0x38-0x3F (example:
REG_TOUCH_CONFIG = 0x0380), while for Goodix IC the I2C address must be set as 0x5D (example:
REG_TOUCH_CONFIG = 0x05D0).
Figure 4-10 Touch Screen Connection
The host controls the CTSE operation mode by writing the REG_CTOUCH_MODE.
REG_CTOUCH_MODE
Mode
Description
0
OFF
Acquisition stopped
1-2
Reserved
Reserved
3
CONTINUOUS
Perform acquisition continuously at the reporting rate of the
connected CTPM.
Table 4-18 Capacitive Touch Controller Operating Mode
The BT815 CTSE supports compatibility mode and extended mode. By default the CTSE runs in
compatibility mode where the touch system provides an interface very similar to the resistive touch
engine. 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).
4.8.3 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).
SCL
RSTN
SDA
INTN
BT815
CTP_SCL
CTP_SDA
CTP_INT_N
CTP_RST_N
Capacitive Touch
Panel Module
VCCIO2
(1.8-3.3V)
1K
1K