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BT817A Automotive Advanced Video Engine Datasheet

Version 1.0

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

0x30210c

REG_EHOST_TOUCH_X

Unsigned

16-bit

Touch x coordinate

0x302118

REG_EHOST_TOUCH_Y

Unsigned

16-bit

Touch y coordinate

0x302114

REG_EHOST_TOUCH_ID

4-bit

Touch ID / phase

0x302170

REG_EHOST_TOUCH_ACK

4-bit

Acknowledgement

Table 4-20

Registers for Touch Host Mode

The host writes raw (x; y) coordinates and IDs to the above registers. Up to 5 touches can be set,

using touch IDs 0-4. The host indicates no touch by supplying coordinates (0x8000; 0x8000). When

the host writes 0xf to the ID register, BT817A sets the ACK register to 0, transforms all the raw

coordinates, and writes the results to the regular touch registers.

Pseudocode:

wait until REG_EHOST_TOUCH_ACK is 1

for each touch:

write x coordinate to REG_EHOST_TOUCH_X

write y coordinate to REG_EHOST_TOUCH_Y

write id to REG_EHOST_TOUCH_ID

write 0xf to REG_EHOST_TOUCH_ID

As soon as BT817A has converted the coordinates, it writes 1 to the ACK register and sets the

INT_CONV_COMPLETE interrupt flag.

The ID should be zero in touch compatibility mode. The host should indicate no touch at all by writing

(0x8000; 0x8000) with ID 0.

In extended mode, the multiple touches may be sent in any order. Any IDs not assigned are assumed

to be not pressed. Again, the host should indicate no touch at all by writing (0x8000; 0x8000) with ID

The host can use three methods to ensure that BT817A is ready to accept touch inputs:

1. poll the ACK register until it is 1

2. use the INT_CONV_COMPLETE interrupt flag

3. supply touches slower than 1000 Hz, since BT817A guarantees to process the

touches in under 1 ms. Note that report rates from capacitive touch panels are about

100 Hz

Like the direct capacitive driver, this touch host mode works when REG_CTOUCH_EXTENDED is both

CTOUCH_MODE_EXTENDED and CTOUCH_MODE_COMPATIBILITY. CTOUCH_MODE_COMPATIBILITY

should be used for the calibration procedure, just as when using native capacitive support. After

changing mode, the BT817A touch engine must be reset.

4.8.6 Touch Detection in none-ACTIVE State

When the BT817A is in non-ACTIVE state, a touch event can still be detected and reported to the host

through the INT_N pin. In other words, a touch event can wake-up the host if needed.

For capacitive touch, the INT_N pin will follow CTP_INT_N pin when the BT817A is in STANDBY, SLEEP

or POWERDOWN state.

4.9 Power Management

4.9.1 Power Supply

The BT817A may be operated with a single supply of 3.3V applied to VCC and VCCIO pins, and a

supply of 1.28V applied to the VCC1V2 pins. For operation with a host MPU/MCU at a lower supply,

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