Direct Operation; Figure 25-6. 5-Wire Feedback (7-Wire) Analog Resistive Interface Switching Diagram - Cirrus Logic EP93 Series User Manual

Analog Touch Screen Interface
EP93xx User's Guide
TOUCH DETECT
SW28
100K
SW22
100K
SW23
SW19
SW11
25
SW20
SW13
SW21
SW0
V+
SW1
V-
SW2
Z+/-
SW3
Z-/+
SW12
SW14
SW4
SW5
SW6
SW7
SW24
sV+
SW25
sV-
SW26
Wiper
Not Used
SW27
SW15
SW16
SW17
SW18

25.2.3 Direct Operation

When the touch screen controller is disabled (TSSetup.ENABLE low), the ARM Core has
direct control of the analog switch array through the TSDirect register. The full 12-bit output of
the analog-to-digital converter can also be read from the TSXYResult register when the touch
screen engine is disabled. Please note that the initial read value should be viewed as a
convert command where the data provided is stale and should be discarded. After the
conversion time for the A / D converter, the actual value may be read. This also sets off
another convert command.
The next few figures demonstrate some special functions that can be implemented with direct
ARM Core control of the switch array. The touch screen can be set up in a way that it can be
disabled for low power mode and still have the ability to interrupt the ARM Core.
shows how to detect a key press in either 4 / 8-wire or 5-wire installations with the touch
screen controller disabled. The TOUCH_PRESS signal in the figure is gated into the interrupt
logic when the touch screen controller is disabled and in low power mode. In this mode, the
clock to the module can be disabled and interrupts will still be generated. The low-power
mode should be entered and exited with the touch screen interrupt disabled, as the
asynchronous operation of this logic could cause glitches on the interrupt line. Entering the
low-power state with interrupts enabled may trigger false interrupts.
25-12
DISCHARGE ALL LINES
TOUCH_PRESS
SW29
DAC
VDD
VBAT
100K
SW22
SW8
100K
SW23
SW30
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
V+
SW1
V-
SW2
Z+/-
Z-/+
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+ sV+
SW25
sV-
SW26
Wiper
Not Used
SW27
REF-
SW15
SW16
SW10
SW17
SW18

Figure 25-6. 5-Wire Feedback (7-Wire) Analog Resistive Interface Switching Diagram

SAMPLE X-AXIS
VDD
100K
100K
A/D CONVERTER
IN
V+
V-
Z+/-
Z-/+
SW9
REF+ sV+
sV-
Wiper
Not Used
REF-
SW10
Copyright 2007 Cirrus Logic
SAMPLE Y-AXIS
VDD
100K
SW22
100K
SW23
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
V+
SW1
V-
SW2
Z+/-
Z-/+
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+ sV+
SW25
sV-
SW26
Wiper
Not Used
SW27
REF-
SW15
SW16
SW10
SW17
SW18
VDD
SW22
SW23
SW19
SW11
SW20
SW13
A/D CONVERTER
SW21
SW0
IN
SW1
SW2
SW3
SW12
SW14
SW4
SW5
SW9
SW6
SW7
SW24
REF+
SW25
SW26
SW27
REF-
SW15
SW16
SW10
SW17
SW18
Figure 25-7
DS785UM1