MK712

Touch Screen Controller

MDS 712 I

8

Revision 100899

Printed 11/16/00

Integrated Circuit Systems, Inc.•525 Race St.•San Jose•CA•95126•(408)295-9800tel•www.icst.com

I C R O

Read Register 0 D7D5, store as D7D5(n)

Wait for Interrupt

Is D7D5(n-1) = 11b

and D7D5(n) =11b?

No

Yes

Write point n-1 to display

Recommended Method for Reading Points

If the user is pressing lightly on the touch screen, it is likely that the screen contact will be intermittent.

The screen will bounce, causing false points. This effect can be reduced by insuring that the screen is

touched both before and after a conversion. By doing this, the first and last point in a series of points

are discarded. The following algorithm checks that a point has valid touches both before and after a

conversion, and it distinguishes between change-in-touch interrupts and conversion complete

interrupts. Register 6 bits 0, 1, and 2 must all be true (logical 1) in order to use this method.

Are this point and the previous point valid?

(11b = binary 11)

Write previous point.

Start

Interrupt

Increment

n

Read X and Y, store as point n

Warning - When Using a Switching Regulator Power Supply

When using the MK712 in a system where the power is supplied by a switching regulator, do not

perform screen conversions when the regulator is operating in the power saving mode. Some switching

regulators feature a low power mode (for example, Linear Technology’s “Burst Mode”) where the

output is turned on and off in order to save power. The extra power supply noise generated when using

this mode causes spurious data points to be returned from the MK712, so it should be disabled when

the MK712 is doing screen conversions.