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Document Number: 001-57308 Rev. *E Page 7 of 39
Power States Summary
The CY8CTMA340 controller includes a configurable power
state machine as shown in Figure 3. There are three separate
states:
■ Active, during which the touchscreen is actively scanned and
new touchscreen data is regularly refreshed
■ Low Power, during which the touchscreen is scanned at a much
slower rate to detect the presence of a finger
■ Deep Sleep, during which the touchscreen is not scanned and
the CY8CTMA340 controller is in a very low power state. The
internal clocks are turned off but the state of all registers and
RAM is maintained.
Figure 3. CY8CTMA340 Power States and Transitions
There are three parameters to configure the power state
machine: Active Refresh Interval (register ACT_INTRVL) defines
the minimum time between the start of subsequent touchscreen
scans in the active state; Touch Timeout (register TCH_TMOUT)
defines the time to stay in the Active state after the last finger is
removed from the touchscreen before transitioning to the Low
Power state; and Low Power Refresh Interval (register
LP_INTRVL) defines the time in the Low Power state between
touchscreen scans. The power state machine is active only when
the CY8CTMA340 controller is communicating in the operating
mode. In all other communication modes, the touchscreen is
scanned continuously. See Communications Protocol Summary
on page 11 for a detailed description of operating mode, system
information mode, and test mode.
At startup in Operating mode, the CY8CTMA340 controller
enters the Active power state. In the Active power state, the
controller periodically scans the panel, determines whether it is
being touched, identifies the finger centroid locations, and
processes these positions and motion into gestures.
In Active state, the Active Refresh Interval register specifies the
scanning/processing cycle interval in milliseconds. If a
touchscreen can be scanned and processed in less time than
specified by the Active Refresh Interval. The controller sleeps for
the remaining time to reduce power consumption. If the scanning
and processing time exceeds the specified actual scanning and
processing cycle interval by the ACT_INTRVL register, scanning
and processing cycles are executed continuously without any
idle or sleep time. Increasing the Active Refresh Interval value
decreases power consumption in the Active state but increases
touchscreen data refresh time.
If the host sets the Low Power bit (bit 2 of the HST_MODE
register) the CY8CTMA340 controller automatically manages
transitions from the Active state to the Low Power state, based
upon finger/touch activity. The Touch Timeout specifies the
minimum time duration (in 10-ms increments) the controller
remains in the Active state after its last detection of touch activity.
After no touch activity has been detected for this time duration,
the controller enters the Low Power state.
In the Low Power state, the Low Power Refresh Interval defines
how often the touchscreen is scanned. Unlike the Active state, in
the Low Power state the finger positions are not updated after a
scan; the controller is only scanning to see whether a finger is
detected. When a finger is detected, the controller transitions to
the active state and begins normal, regular touchscreen
scanning and processing. The host may also clear the Low
Power bit to force the CY8CTMA340 controller out of the Low
Power state and into the Active state. Also, if the host sets the
Deep Sleep bit (bit 1 of the HST_MODE register) while in the Low
Power state, the controller will transition to the Deep Sleep state.
To transition from the Active or Low Power states to the Deep
Sleep state, the host must set the Deep Sleep bit, after which the
CY8CTMA340 controller will put itself in an ultra-low power
condition instead of performing the next touchscreen scan. The
controller remains in the Deep Sleep state until the host pulls the
COMM INT pin low, after which the controller wakes up and
returns to the Active state.
Figure 3 illustrates the three power states and their transitions.
For more information on configuring the behavior of power states
in the CY8CTMA340, refer to the TrueTouch
®
Touchscreen
Controller Standard Product TRM (Technical Reference
Manual).
Active
Deep Sleep
Low Power
Host requests deep sleep
COMM INT pin
pulled low
Touch detected,
or host disables Low Power
Low Power enabled
and no touches detected
for Touch Timeout
Start
Host requests deep sleep