MK712RLF Просмотр технического описания (PDF) - Integrated Device Technology

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MK712RLF

TOUCH SCREEN CONTROLLER

Integrated Device Technology 

MK712

TOUCH SCREEN CONTROLLER

TOUCH SCREEN CONTROL

Optimizing Performance when Reading and Writing Registers

Reading and writing the MK712 generates digital noise that may reduce the accuracy of the A to D converter. This

noise has several causes, including board layout, data bus loading, and power supply voltage. By appropriately

timing the register operations, the effects of this noise can be minimized.

After an interrupt is issued, the MK712 allows a minimum of 1 millisecond to elapse before initiating the conversion

cycle. This allows the screen drivers to settle. For best performance, complete all register operations within this 1ms

window after an interrupt.

Power Down/Stopping the Clock

If the screen is untouched, the supply current is under 3µA. If the input clock is stopped, the supply current is also

less than 3µA. When the screen is touched with no clock, TOUCH goes low and INT goes high, but no further

operations occur until the clock starts. A to D conversions are invalid until after the clock has stabilized at the correct

frequency and one full conversion cycle has been completed.

Input Clock

The MK712 is highly tolerant of different clock frequencies (from 12 to 20 MHz), rise times, and duty cycles.

However, any input clock undershoot or overshoot will cause the MK712 to draw extra current. This can be

eliminated by using a MicroClock clock synthesizer and properly terminating the clock driver. MicroClock makes low

power clock synthesizers with 14.3 MHz power down.

Resistive Touch Screen (4-wire)

Resistive touch screens consist of 2 resistive plates that are separated by a small gap. Each plate has an electrode

at each end and when the screen is touched, the two plates are shorted together at that point.

If a voltage is applied, for example, between XL and XH, then a voltage divider is formed on the X PLATE. When the

Y PLATE is touched to the X PLATE, a voltage will be developed on the Y PLATE that is proportional to distance of

the touch from XL and XH. By accurately measuring this voltage, the position of the touch can be determined.

IDT™ / ICS™ TOUCH SCREEN CONTROLLER

7

MK712

REV L 070805

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