CRTOUCH Datasheet, PDF (19/68 Pages) Freescale Semiconductor, Inc – Capacitive and Resistive Touch Sensing Application Specific IC.

Functional Description
electrodes. For example, E0 corresponds to position 0, E0 and E1 correspond to position 1, and E1 corresponds to position 2.
When more than two electrodes are touched, the central position is reported.
2.3 Modes of operation
The CRTouch operating modes are described in this section. Entry into each mode and exit from each mode as well as the
function while in each of the modes are described.
2.3.1 Run mode
This is the normal operating mode for CRTouch which is the default mode for a new device. In this mode the device is not
entering into low-power nor shutdown modes at any time. Serial communications are active all the time waiting for a command
to be received. Scanning of a resistive touchscreen panel will be performed periodically as defined in the Sampling Rate register.
During run mode, all the internal circuitry remains enabled all the time. All the functions do not have any constraints or special
considerations to be used while in this mode. Power consumption is higher than in any other operating mode.
2.3.2 Sleep mode
Sleep mode is enabled through the SLEEPEN bit in the Configuration Register. This mode sends the part into a low power mode
between scanning periods of a resistive touchscreen panel. When the part is in sleep mode it turns off the internal clocks for the
serial communication peripherals, both UART and I2C. The overall function of the device is the same compared to normal run
mode, with the exception of communication interfaces.
2.3.2.1 CRTouch function in sleep mode
When Sleep mode is enabled, the part will remain in this state until the timeout configured in the Sampling rate register expires.
After the Sampling Rate period expires, the part will start the sequence to scan if the resistive touch screen connected has a new
coordinate and calculate the X and Y coordinates and gestures detection if needed.
Besides a sampling rate period expiration, there are two additional ways to transition from Sleep mode into Run mode:
• Wakeup pin—The active low wakeup pin will transition the part from Sleep mode into run mode. While being asserted,
the device will remain in run mode. The part will return into Sleep mode after the signal has been de-asserted, unless
there is an active communication (UART or I2C) or the part is actively scanning a resistive touchscreen panel. For the
communication case, the communication timeout rules will apply before going back to Sleep mode. When the part is
scanning the resistive touchscreen panel, it will go back to sleep mode as soon as the scanning process finishes.
• Serial communication—Either UART or I2C can transition the part from sleep mode into run mode. Each
communication interface has specific characteristics and rules while working in sleep mode.
2.3.2.2 I2C communication in sleep mode
If I2C communication is selected for CRTouch communication, a start condition followed by a Slave Address match can be
used to wakeup the part from sleep mode and transition to normal run mode. Because the I2C internal clock was turned off until
the slave address matched, CRTouch answers with a Not Acknowledge to this initial request. There are two alternatives to use
I2C communication with Sleep mode enabled:
• Include in the host the logic a re-send of the Slave Address with the appropriate read or write request upon reception
of a not acknowledge.
CRTouch Data Sheet, Rev. 3
Freescale Semiconductor
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