ScreenCoder
TM
UR7HCTS2-S840
High-Performance, Low Power
Touch Screen Controller/Digitizer
HID & SYSTEM MANAGEMENT PRODUCTS, MOUSECODER
TM
FAMILY
DESCRIPTION
The ScreenCoder
TM
SPI/Serial is a
touch screen controller and
integrated digitizer IC designed
specifically for RISC-based
systems, such as wireless Internet
appliances. The small, single
footprint IC interfaces the system
via either the Serial Peripheral
Interface (SPI) or Asynchronous
Serial Interface.
Unlike simple A/D implementations,
the ScreenCoder
TM
SPI/Serial does
not require complicated software
drivers and no processing burden
is placed on the CPU. Due to the
IC’s superior data processing and
sampling rate, the ScreenCoder
TM
SPI/Serial is ideal for use in systems
requiring handwriting recognition.
Patented-power management
techniques are also implemented
so that the IC only consumes 1uA
of current most of the time, even
with the external mouse connected.
The IC operates at 3 to 5 Volts.
Features of Semtech’s motion
algorithm include resistance to RF
and other noise which provides
smooth and precise motion control.
The UR7HCTS2-S840 also works
flawlessly with any 4 or 8-wire touch
screen, regardless of size or
manufacturer.
The cost-effective solution requires
few external components, allowing
for a simple and real estate saving
implementation.
FEATURES
• Touch screen controller / digitizer
in a single, small footprint IC
• Interfaces the system via either
Serial Peripheral Interface (SPI)
and Asynchronous Serial Interface
• Works with any 4- or 8-wire
resistive touch screen, regardless
of size, material or vendor
• Provides high resolution of 1000
points per axis and a sampling
rate of 200Hz
• Accurate, quick touch response
due to advanced sampling
technology and patented
algorithms
• Zero-Power
TM
operation — IC
typically consumes less than 1µA
• Highly resistant to RF and other
noise sources
• Uses sophisticated power
management for maximum power
savings
• Offers external PS/2 port for the
hot-plug connection of an external
PS/2 pointing device
• Capable of providing other
features, such as battery
monitoring and GPIO
• PS/2 and USB interfaces available
• Available in small 7mm X 7mm
32-pin LQFP package
APPLICATIONS
• Wireless Internet Appliances
• Handheld PCs (H/PCs)
PIN ASSIGNMENTS
• Web Phones
• Portable Systems
24
25
_RB
RSVD2
TxD
ISEL/SCLK
SOUT
_PWR_DOWN
SXL
SYT
YT2
XL2
RVSD1
XDAT
XCLK
_LB
XR2
YB2
17
16
_RTS/_SS
XL1
YT1
LQFP
YB1
XR1
VSS
_OSCOUT
OSCIN
32
1
VDD
VSS2
_RESET
VREF
_CTS/_ATN
XPWRS
SXR
SYB
9
8
ScreenCoder, MouseCoder and Self-Power
Management are a trademark of Semtech Corp.
All other trademarks belong to their respective
companies.
Copyright Semtech 2000-2001
DOC7-TS2-S840-DS-102
1
www.semtech.com
ORDERING CODE
Package Options
32-pin, Plastic LQFP
Pitch in mm’s
0.8
TA=-20° C to +85° C
UR7HCTS2-S840-FG
Other Materials
ScreenCoder
TM
SPI/Serial
Type
Evaluation Kit
Order number
EVK7-TS2-S840-XXX
Note 1:
XXX= Denotes Revision number
BLOCK DIAGRAM
Left Button
ASI/SPI
Right Button
ASI/SPI
Communication port
Switch Interface
Power Management
Section
Drivers for Touch
Screen
Touch Panel
Interface
4
Power-On Reset
Sense Line
4
Sensor Interface
16 bit Timer
XCLK
8042 Emulation port
Oscillator Circuit
XDAT
OSCIN
_OSCOUT
Copyright Semtech 2000-2001
DOC7-TS2-S840-DS-102
2
www.semtech.com
PIN DEFINITIONS
Mnemonic Pin #
VDD
8
VSS
11
VSS2
7
OSCIN
9
Type
P
P
P
I
Name and Function
Power Supply
Ground
Ground
Oscillator Input:
external clock input or one
side of the Ceramic Resonator with built-in Load
Capacitors
Oscillator Output:
open for external clock
input or other side of the Ceramic Resonator with
built-in Load Capacitors
Reset:
apply 0V to provide orderly start-up
External Mouse Clock:
PS/2 clock signal from
external mouse; keep open if unused
External Mouse Data:
PS/2 data signal from
external mouse; keep open if unused
Left Button:
active low
Right Button:
active low
Sensor’s Excitation Driver:
connect to X Right
Sensor’s Excitation Driver:connect
toY Bottom
Sensor’s Excitation Driver:connect
to Y Top
Sensor’s Excitation Driver:
connect to X Left
Reference Voltage
for built-in A/D
Sense line:
for X Left
Sense line:
for Y Top
Sense line:
for Y Bottom
Sense line:
for X Right
Hardware Power Down:
tie high if unused
External Mouse Power Sense:
connect to
switched power plane for the external pointing device
or tie high if external mouse port is used; tie low if
external mouse port is unused
Slave Select / Ready To Send:
active low, host
ready to get data
Attention / Clear To Send:
active low, request
data transfer
Data Output:
Serial mode
Interface Select / SPI Clock:
tie low for Serial
Data Output:
SPI mode
Reserved:
Keep open
_OSCOUT
10
O
_RESET
XCLK
XDAT
_LB
_RB
XR1, XR2
12,
YB1, YB2
13,
YT1, YT1
14,
XL1, XL2
15,
VREF
SXL
SYT
SYB
SXR
_PWR_DOWN
XPWRS
6
17
18
24
25
23
22
21
20
5
31
32
1
2
30
3
I
I/O (nd)
I/O (nd)
I/O (nd)
I/O (nd)
I/O
I/O
I/O
I/O
AI
AI
AI
AI
AI
I
AI
_SS/_RTS
_ATN/_CTS
TXD
SCLK/ISEL
SOUT
RSVD1-2
16
4
27
28
29
19,26
I
O
O
I
I/O
I/O
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
Copyright Semtech 2000-2001
DOC7-TS2-S840-DS-102
3
www.semtech.com
FUNCTIONAL DESCRIPTION
The UR7HCTS2-S840 consists functionally of five major sections (see the Functional Diagram). These are the
Sensor Interface, Power Management section, the 16-Bit Timer, the Oscillator Circuit and the Serial Peripheral
Interface (SPI) and the Asynchronous Serial Interface (Serial). All sections communication with each other and
operate concurrently.
OSCILLATOR
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 ScreenCoder
TM
SPI/Serial frequently switches its Oscillator OFF and ON in order to operate with the least amount of power
consumption. Due to very high Q, the Crystal-based oscillators have exceedingly long Start-up time and can not
be used with the ScreenCoder
TM
SPI/Serial .
EXTERNAL PS/2 INTERFACE
There is one external PS/2 port for the connection of standard PS/2 devices, including a Microsoft WheelMouse or
5-Button Mouse. The mouse motion data is sent out in relative format. The external PS/2 port also supports hot-
plug; users can connect the mouse to the system at any time without rebooting.
POWER MANAGEMENT
The ScreenCoder
TM
SPI/Serial implements two power management methods: Self-Power Management
TM
and
System-coordinated Power Management.
Self-Power Management
TM
Self-Power Management
TM
is a method implemented by the IC that, independently of any system intervention,
results in the lowest power consumption possible within the present parameters of its operation. Through Self-
Power Management
TM
, the IC is capable of typically operating at only 1uA, independently of the state of the Host
system. Self-Power Management
TM
primarily determines the actual power consumption of the IC. When the host is
in the active state, the IC can still operate most of the time at only 1uA, even when an active external PS/2 device
is attached to it.
Self-Power Management
TM
offers three modes of operation: Stop, Run and Wait. "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 will revert when it is idle. “Wait” mode is entered when the IC is waiting for a
response or continuation of data stream from the PS/2 device. The duration of wait mode is limited to 40ms, within
which time the IC will either receive new data from the PS/2 device or enter “Stop” mode. Typical power
consumption in this mode is several hundred uAs. “Run” mode is entered briefly, only to process an event. The IC
will only remain in this mode when there are pending tasks, such as PS/2 report reception or initialization of the
PS/2 device.
System Request To Send,
Mouse hot plug or Data Packet,
Touch Screen activity,
Button press
Figure 1:
Self-Power Management
TM
State
RUN
STOP
1s of inactivity
Copyright Semtech 2000-2001
DOC7-TS2-S840-DS-102
4
www.semtech.com
POWER MANAGEMENT (CON’T)
System-coordinated Power
Management
Figure 2:
System-coordinated Power Management
Normal Operation State:
Critical Suspend
In normal operation state, both the
_PWR_DOWN and XPWRS pins are
in high state. The ScreenCoder
TM
SPI/Serial operations are controlled
by Self-Power Management
TM
.
_PWR_DOWN=0
_PWR_DOWN=0
_PWR_DOWN=1
and XPWRS=0
_PWR_DOWN=1
and XPWRS=1
Critical Suspend:
At any time, the Host may negate
the _PWR_DOWN pin in order to
force the ScreenCoder
TM
SPI/Serial
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
ScreenCoder
TM
SPI/Serial will shut
down all of the pointing activities.
Ext Mouse
power down
_PWR_DOWN=1
and XPWRS=0
Normal State
_PWR_DOWN=1
and XPWRS=1
TOUCH SCREEN SENSOR INTERFACE
The ScreenCoder
TM
SPI/Serial can acquire data from any four- or eight-wire
resistive touch screen sensors. 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 will not perform measurements and will 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.
External PS/2 power down:
The ScreenCoder
TM
SPI/Serial
monitors the state of the power
supply rail for 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 will actively
eliminate shot-through current in the
input buffers for the clock and data
lines by driving both low.
The ScreenCoder
TM
SPI/Serial will re-
initialize the external PS/2 pointing
device when the power to the
external PS/2 port is restored.
Copyright Semtech 2000-2001
DOC7-TS2-S840-DS-102
5
www.semtech.com
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