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UR7HCTS2-P840-FG Datasheet(PDF) 4 Page - Semtech Corporation |
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UR7HCTS2-P840-FG Datasheet(HTML) 4 Page - Semtech Corporation |
4 / 16 page FUNCTIONAL DESCRIPTION Copyright ©1999-2001 Semtech Corporation DOC7-TS2-P840-DS-106 www.semtech.com 4 The ScreenCoderTM UR7HCTS2-P840 consists functionally of six major sections (see the Functional Diagram on page 2). These are the Sensor Interface, Power Management section, the 16-Bit Timer, the Oscillator Circuit, the PS/2 Communication Port and the 8042 Emulation Port. All sections communicate with each other and operate concurrently. To obtain position information from the Resistive Touch Screen Sensor, the ScreenCoderTM PS2 uses four internal drivers (two pins for each driver) and four sensing lines. During sampling, first the drivers and sensing lines for X axis are activated, by setting one X driver high and the other X driver low; the drivers for Y axis are set floating. This action produces a voltage gradient across the touch screen's surface in the X direction. The internal A/D measures both the voltage across the activated X plane and the voltage potential between the planes. Next, the drivers for the Y axis are activated, while the drivers for the X axis are set floating. Again, the internal A/D measures both voltage across the activated plane and potential between the planes. The X and Y absolute position information is calculated from these four A/D measurements. Before the measurement of X and Y positions, the ScreenCoderTM PS2 checks if there is any touch pressure applied to the sensor. Proprietary touch detection algorithm performs this test very quickly, accommodating sensors with various plate-to-plate capacitances. Actual measurements are somewhat more complex and are covered by a US and international patent currently pending. 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 ScreenCoderTM PS2 frequently switches its Oscillator OFF and ON in order to operate with the least amount of power consumption. Due to their very high Q, the Crystal-based oscillators have exceedingly long Start-up times and can NOT be used with the ScreenCoderTM PS2. SENSOR INTERFACE OSCILLATOR At start-up, or upon receiving a reset command, the UR7HCTS2-P840 will wait between 300 and 500 milliseconds before sending an AAh to the Host followed by a device ID of 00h. The IC will then set itself to its default values (i.e., Incremental Stream Mode with 1:1 scaling, and a report rate of 100 Hz). The device will then disable itself until an Enable (F4h) command is sent from the Host. PS/2 COMMUNICATION For every correct command or parameter received from the Host, the UR7HCTS2-P840 sends an Acknowledge (FAh). If an invalid command or parameter is received, the UR7HCTS2-P840 issues a Resend Request (FEh). If an invalid input is again received, the device transmits an Error Code (FCh) to the Host. Both Error and Resend Request responses are sent by the device within 25 milliseconds. Host may not issue any new commands until either the ScreenCoderTM PS2 has responded or until 25 milliseconds have elapsed. ERROR HANDLING POWER MANAGEMENT The ScreenCoderTM PS2 implements two power management methods: Self-Power ManagementTM and System-coordinated Power Management. Self-Power Management Self-Power ManagementTM of the ScreenCoderTM PS2 permits, independently of any system intervention, the lowest power consumption possible within the present parameters and conditions of operation. Through Self-Power ManagementTM, the ScreenCoderTM PS2 is capable of operating - most of the time - at only 1uA, independently of the state of the system. |
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