Cirrus Logic EP93xx - Manual (Page 750)

25-12 DS785UM1
Copyright 2007 Cirrus Logic
Analog Touch Screen Interface
EP93xx User’s Guide
2
5
2
5
25
Figure 25-6. 5-Wire Feedback (7-Wire) Analog Resistive Interface Switching Diagram
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.
Figure 25-7
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.
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
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
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
V+
V-
Z+/-
Z-/+
sV+
sV-
Wiper
Not Used
V+
V-
Z+/-
Z-/+
sV+
sV-
Wiper
Not Used
V+
V-
Z+/-
Z-/+
sV+
sV-
Wiper
Not Used
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
V+
V-
Z+/-
Z-/+
sV+
sV-
Wiper
Not Used
DISCHARGE ALL LINES SAMPLE X-AXIS SAMPLE Y-AXIS TOUCH DETECT
SW8
VBAT
TOUCH_PRESS
SW28
SW30
DAC SW29