Figure 25-2, Shows cont, Discharge all lines sample x-axis sample y-axis – Cirrus Logic EP93xx User Manual
Page 743: Touch detect
DS785UM1
25-5
Copyright 2007 Cirrus Logic
Analog Touch Screen Interface
EP93xx User’s Guide
2
5
2
5
25
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.
details the configuration values required for 4-, 5-, 6-, and 8-wire touch screens.
Figure 25-2. 8-Wire Resistive Interface Switching Diagram
DISCHARGE ALL LINES
SAMPLE X-AXIS
SAMPLE Y-AXIS
X+
X-
Y+
Y-
SX+
SX-
SY+
SY-
SW12
SW14
SW13
SW20
A/D CONVERTER
IN
REF+
REF-
VDD
SW21
SW19
SW11
SW0
SW1
SW2
SW3
SW24
SW25
SW26
SW27
100K
SW23
SW22
100K
SW9
SW10
SW6
SW7
SW4
SW5
SW15
SW16
SW17
SW18
X+
X-
Y+
Y-
SX+
SX-
SY+
SY-
SW12
SW14
SW13
SW20
A/D CONVERTER
IN
REF+
REF-
VDD
SW21
SW19
SW11
SW0
SW1
SW2
SW3
SW24
SW25
SW26
SW27
100K
SW23
SW22
100K
SW9
SW10
SW6
SW7
SW4
SW5
SW15
SW16
SW17
SW18
X+
X-
Y+
Y-
SX+
SX-
SY+
SY-
SW12
SW14
SW13
SW20
A/D CONVERTER
IN
REF+
REF-
VDD
SW21
SW19
SW11
SW0
SW1
SW2
SW3
SW24
SW25
SW26
SW27
100K
SW23
SW22
100K
SW9
SW10
SW6
SW7
SW4
SW5
SW15
SW16
SW17
SW18
TOUCH DETECT
X+
X-
Y+
Y-
SW12
SW14
SW13
SW20
A/D CONVERTER
IN
REF+
REF-
VDD
SW21
SW19
SW11
SW0
SW1
SW2
SW3
SW24
SW25
SW26
SW27
100K
SW23
SW22
100K
SW8
VBAT
SW9
SW10
SW6
SW7
SW4
SW5
SW15
SW16
SW17
SW18
TOUCH_PRESS
SX+
SX-
SY+
SY-
SW28
SW30
DAC
SW29