UR7HCTS2-S840 Datasheet, PDF (4/16 Pages) Semtech Corporation – High-Performance, Low Power Touch Screen Controller/Digitizer

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.
Figure 1: Self-Power Management^TM State
System Request To Send,
Mouse hot plug or Data Packet,
Touch Screen activity,
Button press
RUN
1s of inactivity
STOP
Copyright Semtech 2000-2001
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DOC7-TS2-S840-DS-102
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