Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK データシート

 900

SAM9M10 [DATASHEET]

6355F–ATARM–12-Mar-13

When there is no contact, it is not necessary to perform conversion. However, it is important to detect a contact by
keeping the power consumption as low as possible. 

The proposed implementation polarizes the vertical panel by closing the switch on X

P

 and ties the horizontal panel

by an embedded resistor connected to Y

M

. This resistor is enabled by a fifth switch. Since there is no contact, no

current is flowing and there is no related power consumption. As soon as a contact occurs, a current is flowing in
the touch screen and a schmitt trigger detects the voltage in the resistor.

. If this bit is written at 1, the switch on X

P

 and the switch on the resistor are both closed, except when a touch

screen conversion is in progress. 

To complete the circuit, a programmable debouncer is placed at the output of the schmitt trigger. This debouncer is
programmable at 1 ADC Clock period, useful when the system is running at Slow Clock, or at up to 2

15

 ADC Clock

periods, but better used to filter noise on the Touch Screen panel when the system is running at high speed. The
debouncer length can be selected by programming the field PENDBC in 

.

X

P

X

M

VDDANA

GND

Switch 

Resistor

Switch 

Resistor

XPos Measure(Yp)

Y

P

Y

M

Open 

circuit

Rp

X

P

X

M

VDDANA

GND

Switch 

Resistor

Switch 

Resistor

Z1 Measure(Xp)

Y

P

Y

M

Open 

circuit

Rp

X

P

X

M

VDDANA

GND

Switch 

Resistor

Switch 

Resistor

Z2 Measure(Xp)

Y

P

Y

M

Open 

circuit

Rp