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trademarks of Semtech Corporation.
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ScreenCoderŽ PS/2 UR7HCTS2-P540

Controller/Digitizer

for 5-Wire Touch Screens

www.semtech.com

HID & SYSTEM MANAGEMENT PRODUCTS, SCREENCODERŽ FAMILY

DESCRIPTION

FEATURES

APPLICATIONS

ˇ Interactive kiosks
ˇ Portable systems

ˇ Point of sale (POS) terminals
ˇ Industrial & medical systems

The ScreenCoderŽ PS/2 5-wire
UR7HCTS2-P540 is a high-
performance IC that interfaces any
5-wire resistive touch screen to the
standard PS/2 mouse port. Low-
power and tiny, this single IC is
ideal for industrial and medical
systems, portables and interactive
kiosks. It offers an advanced
algorithm for enhanced motion
control as well as an extra port for
hot-plug connection of an external
PS/2 pointing device. Both the
touch screen and the external
device can be operated
oncurrently without any penalty.

The UR7HCTS2-P540 is equipped
with a special command protocol
that enables the touch screen to
operate in either relative (mouse-
like) or absolute positioning mode.
Because the IC interfaces via the
PS/2 mouse port, it can utilize any
standard mouse driver when
operating in relative mode. For
absolute positioning, Semtech
offers a high-functionality driver.
Mice connected to the
ScreenCoderŽ PS/2's external
mouse port always operate in
relative mode, even if the touch
screen is operating in the absolute
mode. The PS/2 communication
channel is bi-directional at 10
kbps.

The ScreenCoderŽ PS/2 offers
built-in A/D. Touch detection and
motion are handled in firmware,
and no digitizer is required. The
cost-effective solution requires few
external components, allowing for
a simple and real estate saving
implementation.

ˇ Embedded touch screen and

external pointing device can
operate concurrently with no
performance penalty

ˇ Supports both absolute and

relative (mouse-like) modes of
operation

ˇ For relative mode, no special

drivers are needed; high-
functionality driver available for
absolute mode

ˇ Supports all commands defined

in the IBM PS/2 mouse
communication protocol, as
well as Semtech's extended PS/2
protocol for ScreenCoderŽ (with
absolute positioning)

ˇ Few external components required
ˇ Available in a low-profile 32-pin

LQFP package

PIN ASSIGNMENTS

SW_AD

SE_AD

SENSE_DRV

SENSE_AD

VREF

RESET

VSS2

VDD

TOUCH
SE2
SW2
NE2
NW2
HDAT
XDAT
XCLK

OCSIN

OSCOUT

VSS

SE1

SW1

NE1

NW1

HCLK

RSVD1

RSVD2

RSVD3

RSVD4

POWER_DOWN

NW_AD

NE_AD

ˇ Controller & digitizer in a single IC;

no need for external A/D

ˇ Interfaces ANY 5-wire resistive

touch screen to standard PS/2
mouse port; regardless of size,
material or vendor

ˇ High resolution, about 1000 points

per axis

ˇ High-performance IC offers

accurate cursor control due to
advanced algorithms

ˇ Low-power consumption, due to

sophisticated power management
states, ideal for battery-operated
systems

ˇ Highly resistant to RF & other

noise

ˇ Enables hot-plug connection of

an external pointing device

PRELIMINARY

Mnemonic

Pin #

Type

Name and Function

VDD

Power supply

VSS

Ground

VSS2

Ground

OSCIN

Oscillator input: external clock input or one
side of the Ceramic Resonator with built-in Load
Capacitors

_OSCOUT

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

_RESET

Reset: apply 0V to provide orderly start-up

XCLK

I/O (nd)

External mouse clock: PS/2 clock signal from
external mouse; keep open if unused

XDAT

I/O (nd)

External mouse data: PS/2 data signal from
external mouse; keep open if unused

_TOUCH

I/O (nd)

Touch detection: active low

_RB

I/O (nd)

Right button: active low

HDAT

I/O (nd)

Mouse data: connects to host's data line

HCLK

I/O (nd)

Mouse clock: connects to host's clock line

_SE1

I/O

Sensor's excitation driver: connect to
South East Corner

_SW1

I/O

Sensor's excitation driver: connect to
South West Corner

_NE1

I/O

Sensor's excitation driver: connect to
North East Corner

_NW1

I/O

Sensor's excitation driver: connect to
North West Corner

NW2

I/O

Sensor's excitation driver: connect to
North West Corner

NE2

I/O

Sensor's excitation driver: connect to
North East Corner

SW2

I/O

Sensor's excitation driver: connect to
South West Corner

SE2

I/O

Sensor's excitation driver: connect to
South East Corner

VREF

Reference voltage for built-in A/D

AD_NW

Sense line: for North West Corner

AD_NE

Sense line: for North East Corner

AD_SW

Sense line: for South West Corner

AD_SE

Sense line: for South East Corner

DRV_SENSE

I/O

Drive Pin for Sense Line

DRV_AD

Sense Pin for Sense Line

_POWER_

Hardware Power Down: tie high if unused

DOWN

RSVD1-4 26-29

I/O

Reserved

Note: An underscore before a pin 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

The ScreenCoderŽ PS/2
UR7HCTS2-P540 consists
functionally of six major sections
(see the block diagram on 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.

FUNCTIONAL DESCRIPTION

PIN DEFINITIONS

OSCILLATOR

PS/2 COMMUNICATION

At start-up, or upon receiving a
reset command, the
UR7HCTS2-P540 waits between
300 and 500 milliseconds before
sending 0xAA to the host, followed
by a device ID of 0x00. The IC
then sets itself to its default values
(i.e., incremental stream mode with
1:1 scaling, and a report rate of
100 Hz). The device then disables
itself until an enable (0xF4)
command is sent from the host.

For every correct command or parameter received from the host, the
UR7HCTS2-P540 sends an acknowledge (0xFA). If an invalid command or
parameter is received, the IC issues a resend request (0xFE). If an invalid
input is again received, the device transmits an error code (0xFC) to the host.

Both error and resend request responses are sent by the device within 25
milliseconds. The host may not issue any new commands until either the IC
has responded or until 25 milliseconds have elapsed.

ERROR HANDLING

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 crystals can
NOT be used. The UR7HCTS2-
P540 frequently switches its
oscillator OFF and ON in order to
operate with the least amount of
power consumption. Due to their
very high Q, crystal-based
oscillators have exceedingly long
start-up times and can NOT be
used with the UR7HCTS2-P540.

www.semtech.com

www.semtech.com

POWER MANAGEMENT

POWER MANAGEMENT (CON'T)

RUN

STOP

System Request To Send,

Mouse hot plug or Data Packet,

Touch Screen activity,

Button press

1s of inactivity

Figure 1: Self-Power ManagementTM State

Figure 2: System-coordinated Power Management

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

Critical Suspend

At any time, the host may negate the _PWR_DOWN pin in order to force
the UR7HCTS2-P540 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 IC shuts down all pointing activities.
However, communications with the host are still enabled.

External PS/2 power down

The UR7HCTS2-P540 monitors the power state of the external PS/2
pointing device through the XPWRS pin. If the IC senses that the external
PS/2 device 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 ScreenCoderŽ PS/2 will re-initializes the external PS/2 pointing device
when the power to the external PS/2 port is restored.

The UR7HCTS2-P540 implements
two power management methods:
Self-Power ManagementTM and
system-coordinated power
management.

Self-Power ManagementTM

Self-Power ManagementTM of the
ScreenCoderŽ PS/2 permits,
independently of any system
intervention, the lowest power
consumption possible within the
present parameters and conditions
of operation. Through Self-Power
ManagemenTM, the IC is capable
of operating - most of the time - at
only 1 ľA, independently of the
state of the system.

Stop mode is the lowest power
consumption mode. In this mode,
the oscillator is stopped, and the
IC consumes only the leakage
current. This is the default mode
to which the IC reverts when it is
idle. An event or signal conditions
wake up the IC. The
UR7HCTS2-P540 can still operate
most of the time at only1 ľA, even
when the host is in the active state,
and with active external PS/2
device attached to the IC. If an
external PS/2 device sends a data
packet, the ScreenCoderŽ P/S2
exits the stop 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.

System-coordinated Power
Management

Normal Operation State

In normal operation state, both
_PWR_DOWN and XPWRS pins are
in high state. ScreenCoderŽ PS2
operations are controlled by Self-
Power ManagementTM.

www.semtech.com

SENSOR INTERFACE

The UR7HCTS2-P540 can acquire data from ANY five-wire resistive touch screen sensor, regardless of size,
material or vendor. The sensor interface has the following features:

Touch detection

The IC periodically checks touch pressure applied to the panel. If there is no touch, the IC does not perform
measurements and does not send data to system. When touch pressure is detected, the IC further qualifies and
determines the amount of pressure. Semtech's proprietary, patent-pending touch detection algorithm performs this
test very quickly, accommodating sensors with various plate-to-plate capacitances.

Touch Measurement

Position information is only collected if it has been determined that the touch pressure is sufficient for an accurate
reading. The 5-wire touch screen has two panels. One is the resistive panel for supplying the voltage gradient.
The other is the conductive panel used to get the touch voltage. To obtain position information from the resistive
touch screen sensor, the UR7HCTS2-P540 uses four internal drivers (three pins for each driver) and one sense line.
During sampling, the drivers of the X-axis are activated by setting one X-drive high and the other X-drive low. The
sense plane is 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. Again, the internal A/D measures both voltage across the
activated plane and potential between the planes. 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 data processing delivers
consistent position accuracy and quick touch response.

Resolution

The UR7HCTS2-P540 uses a built-in A/D converter to get the touch position. The maximum absolute position
resolution is 1000 points per direction. Resolution varies somewhat for different touch screen sensors, due to
voltage droop on connecting wires and sensor's mechanical construction.

Touch screens from different makers

Operating parameters for the touch screens from different manufacturers vary depending on the size of the sensor,
material it is made from, and mechanical construction. The UR7HCTS2-P540 takes these properties into account,
and adjusts automatically for plate-to-plate capacitance, intrinsic plate resistances, etc. The IC can support every
kind of 5-wire touch screen, no matter the makers and materials.

Touch-screen coordinates

The zero point for the touchscreen is at the left upper corner. See the diagram.

Buttons

The UR7HCTS2-P540 implements right button. The button information is combined
with external mouse's buttons information when it is sent to the system.

(0,0)

Part Number UR7HCTS2-P540