WM9713 Datasheet, PDF (63/111 Pages) Wolfson Microelectronics plc – AC 97 AUDIO + TOUCHPANEL CODEC

Preliminary Technical Data
WM9713L
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.
REGISTER
ADDRESS
78h
BIT LABEL DEFAULT
DESCRIPTION
12 45W
8
PIL
0:5 RPU
0 (4-wire)
0 (200µA)
000001
(64kΩ)
Touchpanel Type Selection
0: 4-wire
1: 5-wire
Current used for pressure measurement
0: IP = 200µA
1: IP = 400µA
Internal Pull-up resistor for Pen Detection
111111: 64kΩ/63 = 1.02kΩ (least sensitive)
111110: 64KΩ/62 = 1.03KΩ
… (pull-up = 64kΩ / binary value of RPU)
000010: 64KΩ/2 = 32KΩ
000001: 64kΩ/1 = 64kΩ (most sensitive)
000000: RESERVED (do not use this setting)
Table 45 Touchpanel Digitiser Control (Physical Characteristics)
1
PTD, March 2004, Rev 2.2
63