© 2009 Microchip Technology, Inc.

DS41393A-Page 5

7.3

4, 5, 8-Wire Sensor Selection

The desired sensor type of 4/8-Wire or 5-Wire is hardware selectable using pin M2.

Type

M2 pin

4/8-wire

VSS

5-wire

VDD

Table 4 : 4/8-wire vs 5-wire Selection

If 4/8-wire has been hardware selected, then the choice of 4-wire or 8-wire is software selectable, via the

TouchOptions

configuration register. When 4/8-Wire is hardware selected, the controller defaults to 4-wire

operation. If 8-wire operation is desired, then the TouchOptions configuration register must be changed.

7.4

4-wire Touch Sensor Interface

Sensor tail pin-outs can vary by manufacturer and part number. Ensure both sensor tail pins for one sensor axis

(layer) are connected to the controller’s X–/X+ pins and the tail pins for the other sensor axis (layer) are

connected to the controller’s Y–/Y+ pins. The controller’s X–/X+ and Y–/Y+ pin pairs do not need to connect to a

specific sensor axis. The orientation of controller pins X– and X+ to the two sides of a given sensor axis is not

important. Likewise, the orientation of controller pins Y– and Y+ to the two sides of the other sensor axis is not

important.

Connections to a 4-wire touch sensor are as follows.

Figure 4 : 4-wire Touch Sensor Interface

Tie unused controller pins 5WSX-, SX+, SY-, and SY+ to VSS.

The capacitance of alternate ESD diodes may adversely affect touch performance. A lower

capacitance is better. The PESD5V0S1BA parts shown in the reference design have a typical

capacitance of 35pF. Test to ensure that selected ESD protection does not degrade touch

performance.

ESD protection is shown in the reference design, but acceptable protection is dependent on your

specific application. Ensure your ESD solution meets your design requirements.