ACT5880 datasheet(75/87 Pages) ACTIVE-SEMI

75 / 87 page

ACT5880

Rev 2, 03-Sep-13

- 75 -

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TSC ADC Registers

The conversion manipulation and the configuration

are all user accessible through the register bits

writing or reading. Purposes of most register bits

are straight and clear, refer to the REGISTER AND

BIT DESCRIPTIONS

section for detail.

Acquisition Configuration

The whole TSC ADC circuit could be disabled by

setting the nEN bit for reducing the operation current.

For any TSC ADC operation, clear the nEN bit to 0

firstly.

The acquisition configuration includes how an

acquisition is started, how conversions are grouped

in an acquisition, the conversion length selection,

the calibration time selection, the conversion clock

divider selection, and selection of sampling to

conversion start delay.

The analogue front end only provides force driving

to the touch panel when the group scan to touch

screen interface is selected, which reduces the

power consumption for driving the panel when it is

not measured. When the group scan is not

selected, 3 of the 4 touch screen interface pins

could be used as normal input path for ADC.

Interrupts and Status Bits

If not masked, interrupt is asserted when a touch is

detected and/or an acquisition is done and the

result waits for being read. Each of the interrupt

conditions could be masked by its mask bit and the

status of the detection and acquisition could be

read through the I2C interface, regardless if it is

masked. Refer to the REGISTER AND BIT

DESCRIPTIONS

section for detail.

Application Program Consideration

Touch spot tracking desires intensive computing.

Dynamic

processing

resource

allocation

and

interrupt mask reconfiguration are necessary to

accelerate the tracking process.

Before any touch press is detected, the TSC ADC is

set to wait for touch press event and to assert

interrupt when a touch is detected. When touch

press is ever detected, the pen-touch detection

interrupt should be masked and the interrupt

disposing routine should initialize for a polling

routine which starts conversion and reads result

with a fix time interval.

When applying the force voltage onto one layer of

the touch screen, a coupled voltage is seen at

another layer through the layer to layer capacitance

if there is no effective resistive leakage path at the

another layer. This mechanism causes a false

touching at the first time enabling the pen touch

detection function, which should be ignored by

application software. This mechanism also causes

false reading of around center point touching if

reading without touching detected firstly. There is

no false reading in automatic conversion operation

when the nAUTO[ ] is cleared to 0, where the

conversion starts only when touching is detected.

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