FUNCTIONAL DESCRIPTION

Copyright ©1999-2001 Semtech Corporation

DOC7-TS2-P840-DS-106

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4

page 2). These are the Sensor Interface, Power Management section, the 16-Bit Timer, the Oscillator Circuit, the

PS/2 Communication Port and the 8042 Emulation Port. All sections communicate with each other and

operate concurrently.

To obtain position information from

the Resistive Touch Screen Sensor,

internal drivers (two pins for each

driver) and four sensing lines.

During sampling, first the drivers

and sensing lines for X axis are

activated, by setting one X driver

high and the other X driver low;

the drivers for Y axis are set

floating. This action produces a

voltage gradient across the touch

screen's surface in the X direction.

The internal A/D measures both the

voltage across the activated X

plane and the voltage potential

between the planes. Next, the

drivers for the Y axis are activated,

while the drivers for the X axis are

set floating. Again, the internal A/D

measures both voltage across the

activated plane and potential

between the planes. The X and Y

absolute position information is

calculated from these four A/D

measurements.

Before the measurement of X

PS2 checks if there is any touch

pressure applied to the sensor.

Proprietary touch detection

algorithm performs this test very

quickly, accommodating sensors

with various plate-to-plate

capacitances. Actual

measurements are somewhat more

complex and are covered by a US

and international patent currently

pending.

This IC has a built-in Oscillator circuit capable of operations with an

external 4.00 MHz Clock source, or a Ceramic Resonator (preferably with

built-in Load Capacitors). Note that the Crystals can NOT be used. The

to operate with the least amount of power consumption. Due to their very

high Q, the Crystal-based oscillators have exceedingly long Start-up times

SENSOR INTERFACE

OSCILLATOR

At start-up, or upon receiving a reset command, the UR7HCTS2-P840 will

wait between 300 and 500 milliseconds before sending an AAh to the Host

followed by a device ID of 00h. The IC will then set itself to its default

values (i.e., Incremental Stream Mode with 1:1 scaling, and a report

rate of 100 Hz). The device will then disable itself until an Enable (F4h)

command is sent from the Host.

PS/2 COMMUNICATION

For every correct command or parameter received from the Host, the

UR7HCTS2-P840 sends an Acknowledge (FAh). If an invalid command or

parameter is received, the UR7HCTS2-P840 issues a Resend Request

(FEh). If an invalid input is again received, the device transmits an Error

Code (FCh) to the Host.

Both Error and Resend Request responses are sent by the device within 25

milliseconds. Host may not issue any new commands until either the

ERROR HANDLING

POWER MANAGEMENT

Self-Power Management

independently of any system intervention, the lowest power consumption

possible within the present parameters and conditions of operation.

operating - most of the time - at only 1uA, independently of the state of the

system.