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MK715

Optimizing Performance when Reading and Writing Registers

Reading and writing the MK715 generates digital noise that may reduce the accuracy of the A to D converter. This

noise has several causes, including board layout, and power supply voltage. By appropriately timing the register

operations, the effects of this noise can be minimized.

After an interrupt is issued or RDIPT is asserted, the MK715 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.

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.