ACT5880
Rev 2, 03-Sep-13
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.
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
www.active-semi.com
Copyright © 2013 Active-Semi, Inc.
Active-Semi Confidential―Do Not Copy or Distribute
ActivePMUTM and ActivePathTM are trademarks of Active-Semi.
I2CTM is a trademark of NXP.
- 75 -
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
