Figure 25-2. 8-Wire Resistive Interface Switching Diagram - Cirrus Logic EP93 Series User Manual

array scanning and enable the state machine. In determining a touch point, the first axis to be
scanned is the X-axis. X and Y axis definitions are arbitrary and must only be coordinated
with the code when determining a screen position. For 8-wire and 4-wire implementations,
the touch screen X and Y axis positioning should be linear for all checking algorithms to work
linearly. The algorithm and the returned values will not be linear for a 5-wire touch screens or
7-wire (5-wires with feedback) touch screens and must be adjusted by software to determine
screen position. Some newer technology 5-wire touch screens approach linearity and will
need to be adjusted differently in software.
The same algorithm for sampling is used by 4, 5, 7, and 8-wire touch screens. However, the
switch combinations controlled by the algorithm are determined by configuration registers.
The configuration registers are set up by software according to the touch screen type.
Table 25-2 details the configuration values required for 4-, 5-, 6-, and 8-wire touch screens.
TOUCH DETECT
TOUCH_PRESS
SW28
SW29
VDD
100K
SW22
SW8
100K
SW23
SW30
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
X+
SW1
X-
SW2
Y+
Y-
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+
SX+
SW25
SX-
SW26
SY+
SY- SW27
REF-
SW15
SW16
SW10
SW17
SW18
DS785UM1
DISCHARGE ALL LINES
DAC
VDD
VBAT
100K
SW22
100K
SW23
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
X+
SW1
X-
Y+ SW2
Y-
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+
SX+
SW25
SX-
SW26
SY+
SW27
SY-
REF-
SW15
SW16
SW10
SW17
SW18

Figure 25-2. 8-Wire Resistive Interface Switching Diagram

Copyright 2007 Cirrus Logic
Analog Touch Screen Interface
SAMPLE X-AXIS
VDD
100K
SW22
100K
SW23
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
X+ X+
SW1
X-
Y+ SW2 Y+
Y-
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+
SX+ SX+
SW25
SX- SX-
SW26
SY+ SY+
SW27
SY- SY-
REF-
SW15
SW16
SW10
SW17
SW18
EP93xx User's Guide
SAMPLE Y-AXIS
VDD
100K
SW22
100K
SW23
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
SW1
X-
SW2
Y-
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+
SW25
SW26
SW27
REF-
SW15
SW16
SW10
SW17
SW18
25-5
25