Cirrus Logic EP93xx - Manual (Page 747)

DS785UM1 25-9
Copyright 2007 Cirrus Logic
Analog Touch Screen Interface
EP93xx User’s Guide
2
5
2
5
25
Figure 25-4. Analog Resistive Touch Screen Scan Flow Chart
START
SCAN X-AXIS
DISCHARGE ALL FOR
PRESET SETTLING TIME
APPLY VOLTAGE TO
X-AXIS
DELAY FOR PRESET
SETTLING TIME
TAKE 4,8,16,OR 32
SAMPLES STORING
MAX,MIN,AND AVERAGE
ABS(MAX-MIN)
LESS THAN X
DEVIATION
or DEVTMR
carry?
Y
N
ABS(X-XLAST)
GREATER THAN
XMAX?
Y
N
X INT PENDING?
Y
N
SET X INT PENDING
XLAST = X
SCAN Y-AXIS
DISCHARGE ALL FOR
PRESET SETTLING TIME
APPLY VOLTAGE TO
Y-AXIS
DELAY FOR PRESET
SETTLING TIME
TAKE 4,8,16,OR 32
SAMPLES STORING
MAX,MIN,AND AVERAGE
N
SET X INT PENDING
XLAST = X
N
ABS(X-XLAST) LESS
THAN XMIN?
Y
Y
ABS(Y-YLAST)
GREATER THAN
YMAX?
Y
N
Y INT PENDING?
Y
N
SET Y INT PENDING
YLAST = Y
SET INTERRUPT
YLAST = Y
N
ABS(Y-YLAST) LESS
THAN YMIN?
Y
N
X INT PENDING?
Y
SETTLING TIME FOR KEY
DETECTION
WAIT FOR TOUCH PRESS
ABS(MAX-MIN)
LESS THAN Y
DEVIATION
or DEVTMR
carry?