WM9713 datasheet(63/111 Pages) WOLFSON

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Preliminary Technical Data

WM9713L

PTD, March 2004, Rev 2.2

Figure 23 Pen Down Detection on 5-wire Touchpanel

Pen down detection works in a similar fashion for both 4-wire and 5-wire touchpanels (see Four-Wire

Touchpanel Operation). On a 5-wire touchpanel, all four contacts of the bottom plate are grounded,

and the top plate contact is connected to the internal programmable pull-up resistor, RPU.

CONTROLLING THE TOUCHPANEL DIGITISER

All touchpanel functions are accessed and controlled through the AC-Link interface.

PHYSICAL CHARACTERISTICS

The physical characteristics of the touchpanel interface are controlled through register 78h, as shown

below.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

45W

0 (4-wire)

Touchpanel Type Selection

0: 4-wire

1: 5-wire

PIL

0 (200

µA)

Current used for pressure measurement

0: IP = 200

µA

1: IP = 400

µA

78h

0:5

RPU

000001

(64k

Ω)

Internal Pull-up resistor for Pen Detection

111111: 64k

Ω/63 = 1.02kΩ (least sensitive)

111110: 64K

Ω/62 = 1.03KΩ

… (pull-up = 64k

Ω / binary value of RPU)

000010: 64K

Ω/2 = 32KΩ

000001: 64k

Ω/1 = 64kΩ (most sensitive)

000000: RESERVED (do not use this setting)

Table 45 Touchpanel Digitiser Control (Physical Characteristics)

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