Semtech, the Semtech logo, ScreenCoder, and
Self-Power Management are marks of Semtech
Corporation. All other marks belong to their
respective companies.

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UR7HCTS2 ScreenCoder®

PS/2, Asynchronous Serial, and SPI Interface

Touch Screen Controller

HID & SYSTEM MANAGEMENT PRODUCTS, SCREENCODER® FAMILY

DESCRIPTION

FEATURES

SYB/SW_AD

SXR/SE_AD

PWRS/SENSE_DR

SENSE_AD

VREF

_RESET

VSS2

VDD

_LB/_T

OUCH

XR2/SE2

YB2/SW2

YT2/NE2

XL2/NW2

HDA

T/_CTS/_A

XDA

XCLK

_RB

SERSEL

TxD

SCLK

SOUT

_PWR_DOWN

SXL/NW_AD

SYT/NE_AD

HCLK/_RTS/_SS
XL1/NW1
YT1/NE1
YB1/SW1
XR1/SE1
VSS
_OSCOUT
OSCIN

UR7HCTS2-FG

LQFP

The UR7HCTS2 ScreenCoder® is
a touch screen controller with an
integrated digitizer. It works with
any 4-wire, 5-wire, or 8-wire
resistive touch screen, regardless
of size or manufacturer. The
controller interfaces to the host
system via PS/2, asynchronous
serial, or SPI (serial peripheral
interface).

Unlike standalone digitizer designs,
which relegate the entire workload
to the host processor, the low-
power-consuming UR7HCTS2
integrates the digitizer, controller,
and both host system and sensor
interfaces. This greatly reduces
design complexity, development,
integration effort, and cost.

The UR7HCTS2 performs all touch
detection (from finger or pen input),
noise and RF filtering, and error
elimination tasks, supplying fully
processed, stable position data to
the host processor.

The UR7HCTS2's internal power
management technique employs
proprietary motion algorithms and
advanced sampling technology,
allowing the UR7HCTS2 to
consume a mere 1 µA of current
while no event occurs.

The device also provides system
wake-up either by touching the
screen or moving a mouse
connected to its external PS/2 port.
The UR7HCTS2's power
consumption is 3 mA only while an
event occurs.

Semtech's proprietary algorithm
samples at a rate of 100 points per
second.

· Resolution of 1024 points per axis

and a sampling rate of 100 points
per second

· Accurate, quick touch response

triggers system wake-up

· Highly resistant to RF and other

noise sources

· External PS/2 port for the hot-plug

connection of a PS/2 mouse

· Interfaces host system via PS/2,

asynchronous serial, or SPI (serial
peripheral interface)

· Works with any 4-, 5-, or 8-wire

resistive touch screen, regardless
of size or manufacturer

· Low-power operation, typically less

than 1 µA

· Touch screen controller in an LQFP

package

· Notebook computers
· Next-generation cell phones
· Handheld PCs (H/PCs)
· PDAs

· Smart phones
· Interactive kiosks
· Point-of-sale (POS) terminals

APPLICATIONS

PIN ASSIGNMENTS

FUNCTIONAL DESCRIPTION

PIN DEFINITIONS

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Mnemonic

Pin/Lead Type

Name and Function

_PWR_DOWN

4/8-wire: hardware power down: tie high if
unused; 5-wire: leave open

VDD

Power supply

VSS

Ground

VSS2

Ground

_RESET

Reset: apply 0 V to provide orderly start-up

_OSCOUT

Oscillator output: open for external clock input or
one side of the ceramic resonator with built-in
load capacitors

OSCIN

Oscillator input: external clock input or one side
of the ceramic resonator with built-in load
capacitors

HCLK/_RTS/_SS

I/O (pu) PS/2: clock line to host; Serial: input, active low,

ready-to-send; SPI: input, active low, slave select;

HDAT/_CTS/_ATN

I/O (pu) PS/2: data line to host; Serial: output, clear-to-

send; SPI: ouput, attention

SCLK

I/O

PS/2: leave open; Serial: tie to ground;
SPI: clock line

SERSEL

I/O

PS/2: leave open;
Serial, SPI: tie to XR and XR2

SOUT

PS/2, Serial: leave unconnected; SPI: output data

TxD

PS/2, SPI: leave unconnected; Serial: output data

XCLK

I/O (pu) PS/2 clock signal from external mouse; leave

open if unused

XDAT

I/O (pu) PS/2 data signal from external mouse; leave

open if unused

_LB/_TOUCH

I/O (nd) 4/8-wire: left button, active low, strobed sampling;

5-wire: touch detection, active low

_RB

I/O (nd) Right button: active low, strobed sampling

SENSE_AD

I/O

4/8-wire: leave unconnected;
5-wire: connect to sense line

SXL/NW_AD

Sense line: 4/8-wire: X Left; 5-wire: North West

SXR/SE_AD

Sense line: 4/8-wire: X Right; 5-wire: South East

SYB/SW_AD

Sense line: 4/8-wire: Y Bottom;
5-wire: South West

SYT/NE_AD

Sense line: 4/8-wire: Y Top; 5-wire: North East

VREF

Reference voltage for built-in A/D

XL1/NW1

I/O

Excitation driver: 4/8-wire: X Left;
5-wire: North West

XL2/NW2

I/O

Excitation driver: 4/8-wire: X Left;
5-wire: North West

XPWRS/SENSE_DRV 3

4/8-wire: external mouse power sense: tie high
(can not be left floating);
5-wire: driver for sense line

XR1/SE1

I/O

Excitation driver: 4/8-wire: X Right;
5-wire: South East

XR2/SE2

I/O

Excitation driver: 4/8-wire: X Right;
5-wire: South East

YB1/SW1

I/O

Excitation driver: 4/8-wire: Y Bottom;
5-wire: South West

YB2/SW2

I/O

Excitation driver: 4/8-wire: Y Bottom;
5-wire: South West

YT1/NE1

I/O

Excitation driver: 4/8-wire: Y Top;
5-wire: North East

YT2/NE2

I/O

Excitation driver: 4/8-wire: Y Top;
5-wire: North East

Note:

An underscore before a pin/lead mnemonic denotes an active low signal.

Pin Types Legend:

AI=Analog Input; I=Input; O=Output; I/O=Input or Output;

I/O (nd) = Input or Output with N-channel Open Drain driver
I/O (pu) = Input or Output with internal pull-up

The UR7HCTS2 ScreenCoder®
consists functionally of several
major sections shown in the block
diagram on page 2, including the
sensor interface, the power
management section, the 16-bit
timer, the oscillator circuit, and the
host interface. All sections
communicate with each other and
operate concurrently.

The UR7HCTS2 has a built-in
oscillator circuit capable of
operating with an external
4.00 MHz ceramic resonator
(preferably with built-in load
capacitors).

Note:

Crystals can NOT be used

with the UR7HCTS2, because of
their long start-up time. The
UR7HCTS2 frequently turns its
oscillator off to minimize power
consumption.

OSCILLATOR

EXTERNAL PS/2 INTERFACE

The UR7HCTS2 has one hot-
pluggable, hot swappable, auto-
detecting external PS/2 port for the
connection of a standard PS/2
mouse (including a wheel mouse or
5-button mouse). On power-up or
PS/2 hot plug, the device
recognizes what type of mouse is
plugged in.

The device accepts button, wheel,
and relative motion data from the
external mouse and returns it in a
relative position data packet to the
host.

If the power supply voltage is lower
than the PS/2 standard (e.g.,
3.3 V), the external mouse must be
low voltage compatible.

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POWER MANAGEMENT

The UR7HCTS2 implements two power management methods: Self-Power ManagementTM and system-
coordinated power management.

Self-Power ManagementTM

Self-Power ManagementTM of the UR7HCTS2 permits, independently of any system intervention, the lowest power
consumption possible within the present parameters and conditions of operation. Through Self-Power
ManagementTM, the UR7HCTS2 can operate on only 1 µA, most of the time, independently of the state of the
system.

The "Stop" mode is the lowest power consumption mode. In this mode, the oscillator is stopped and the
UR7HCTS2 consumes only leakage current. This is the default
mode, which the device enters when it is idle. An event or signal
condition wakes up the device. The UR7HCTS2 can still operate
most of the time at only 1 µA, even when the host is in the active
state, and with an active mouse attached to the UR7HCTS2's
external PS/2 port. If the external mouse sends a data packet, the
UR7HCTS2 enters "Run" mode for as long as it takes to process the
message and relay the information to the system. This operation is
done transparently to the host, without any data loss or any
response delay from the input device.

RUN

STOP

System Request To Send,

Mouse hot plug or Data Packet,

Touch Screen activity,

Button press

1s of inactivity

Figure 1:

Self-Power Management

State

Host request

Screen activity

Button press

External PS/2 activity

System-coordinated Power Management

Note:

The UR7HCTS2 supports System-coordinated Power Management only in 4/8-wire sensor configurations.

Normal Operation State

In normal operation state, both the _PWR_DOWN and XPWRS pins are in high state. The UR7HCTS2 operations
are controlled by Self-Power ManagementTM.

Critical Suspend

At any time, the host may negate the _PWR_DOWN pin in order to force the device into a "critical suspend" mode.
This signal can be activated (driven low) due to specific conditions of the host's operations (for example, a
discharged battery), or due to actions of the operating
system or BIOS.

During the "critical suspend", the device shuts down all of
its pointing activities.

External PS/2 power down

The UR7HCTS2 monitors the state of the power supply rail
for the external PS/2 mouse through the XPWRS pin. If the
device senses that the external PS/2 mouse has been
powered-down by the host, it actively eliminates shot-
through current in the input buffers for the clock and data
lines by driving both low.

The UR7HCTS2 re-initializes the external PS/2 mouse
when power to the external PS/2 port is restored.

Critical Suspend

Ext Mouse

power down

Normal State

_PWR_DOWN=0

_PWR_DOWN=1
and XPWRS=1

_PWR_DOWN=0

_PWR_DOWN=1
and XPWRS=1

_PWR_DOWN=1
and XPWRS=0

Figure 2:

System-coordinated Power Management

TOUCH SCREEN SENSOR INTERFACE

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The UR7HCTS2 ScreenCoder® can acquire data from any 4-wire, 5-wire, or 8-wire resistive touch screen sensor.

Touch detection

If there is no touch, the IC does not perform measurements and does not send data to the system. When plate-to-

plate conductance is detected, the IC qualifies the touch based on the conductance detected. Semtech's proprietary

touch qualification algorithm works quickly (since data need not be collected over time for filtering), and

accommodates sensors with various plate-to-plate capacitances and impedances.

Touch Measurement (4/8-wire sensors)

Position information is collected only if the plate-to-plate conductance is sufficient for an accurate reading. To obtain

position information from the resistive touch screen sensor, the UR7HCTS2 uses four internal drivers (two pins for

each driver) and four sense lines. During sampling, the drivers of the X-axis are activated by setting one X-drive

high and the other X-drive low. The drivers for the Y-axis are set floating. This 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 at the contact point. Next, the drivers for the Y-axis are activated while the drivers

for the X-axis are set floating. The internal A/D measures both voltage across the activated plane and potential at

the contact point. The X and Y absolute position is obtained from these four A/D measurements. The device keeps

monitoring the conductance even while the positioning data is being acquired. If insufficient conductance is

detected during sampling of the position, the current data set is rejected.

Touch Measurement (5-wire sensors)

Position information is collected only if the plate-to-plate conductance is sufficient for an accurate reading. The

5-wire touch screen has two layers. One is the resistive layer for supplying the voltage gradient. The other is the

conductive layer used to get the touch voltage. To obtain position information from the resistive touch screen

sensor, the UR7HCTS2 uses four internal drivers (two pins for each driver) and one sense line. During sampling,

the drivers for the top corners (northeast and northwest) are set high and the drivers for the bottom corners

(southeast and southwest) are set low. The sense plane is set floating. This produces a voltage gradient across the

touch screen's surface in the Y direction. The internal A/D measures both the voltage across the activated Y-plane

and the voltage potential at the contact point, determining the Y position. Next, the drivers for the left corners

(northwest and southwest) are set high and those for the right corners are set low. Again, the internal A/D measures

both voltage across the activated plane and potential at the contact point, determining the X position. The X and Y

absolute position is obtained from these A/D measurements.

Touch algorithm

Due to vibration and electrical noise, the raw data can not be used directly. Internal digital signal processing

delivers consistent position accuracy and quick touch response.

Resolution

The maximum touch screen resolution with the UR7HCTS2 is 1024 points per axis. Resolution varies somewhat for

different touch screen sensors, due to voltage droop on connecting wires from the parastic capacitance and

resistance of the sensor.

Speed

The UR7HCTS2 samples up to 100 points per second. Each point is one coordinate pair: an X value and a Y value.

Touch screens from different manufacturers

Operating parameters for touch screens from different manufacturers vary depending on the size of the sensor,

material it is made from, and mechanical construction. The UR7HCTS2 takes these properties into account, and

adjusts automatically for plate-to-plate capacitance, intrinsic plate resistances, etc.

Buttons

The UR7HCTS2 implements left and right buttons. The button information is combined with the external mouse's

button information when it is sent to the system.

Note:

Typically, the buttons are not used; they are implemented, and provided in the evaluation kit, as a

development aid.

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