UR7HCTS2-S840 Datasheet, PDF (5/16 Pages) Semtech Corporation – High-Performance, Low Power Touch Screen Controller/Digitizer

POWER MANAGEMENT (CON’T)
System-coordinated Power
Management
Figure 2: System-coordinated Power Management
Normal Operation State:
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.
Critical Suspend
_PWR_DOWN=0
_PWR_DOWN=1
and XPWRS=0
_PWR_DOWN=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.
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.
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.
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
5
DOC7-TS2-S840-DS-102
www.semtech.com