ad7879-1acbz-rl Analog Devices, Inc., ad7879-1acbz-rl Datasheet - Page 29

• Manufacturer Part Number: ad7879-1acbz-rl
• Description: Low Voltage Controller For Touch Screens
• Manufacturer: Analog Devices, Inc.

SCREEN
SCREEN
When the screen is touched, PENIRQ goes low. This generates
an interrupt request to the host. When the screen touch ends,
and if the ADC is idle, PENIRQ immediately goes high. If the
ADC is converting, PENIRQ goes high when the ADC becomes
idle. The PENIRQ operation for these two conditions is shown
in
STATUS
STATUS
PENIRQ
PENIRQ
Figure 36
ADC
ADC
Figure 36. PENIRQ Operation for ADC Idle and ADC Converting
TOUCHED
TOUCHED
NOT
NOT
.
ADC IDLE
PENIRQ
DETECTS
TOUCH
PENIRQ
DETECTS
TOUCH
TOUCHED
TOUCHED
(END OF CONVERSION SEQUENCE)
(GPIO ALERT/OUT OF LIMITS)
ADC IDLE
CONVERTING
DETECTION
ADC
ENABLE
CIRCUIT
PENIRQ
RELEASE NOT
DETECTED
DAV
INT
PENIRQ
DETECTS
RELEASE
YES
ADC IDLE
TOUCH SCREEN TOUCHED
PENIRQ
DETECTS
RELEASE
TOUCHED
TOUCHED
Figure 37. Master Mode Operation
NOT
NOT
ADC MODE = 11?
MASTER MODE
0
1
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CONTROL REGISTER 3
BIT 13
TOUCH SCREEN TOUCHED
INT/DAV/GPIO ALERT
YES
SYNCHRONIZING THE AD7879 TO THE HOST CPU
The two recommended methods for synchronizing the AD7879
to its host CPU are slave mode (in which the mode bits can be
either 01b or 10b) and master mode (in which the mode bits
are 11b).
In master mode (ADC mode bits = 11b), PENIRQ mode can
be used as an interrupt to the host. When PENIRQ goes low to
indicate that the screen has been touched, the host is awakened.
The host can then program the AD7879 to convert in any mode
and read the results after the conversions are completed.
In master mode, INT or DAV can also be used as an interrupt
to the host. The host should first define a conversion sequence
in Control Register 3, initialize the AD7879 in Mode 11b and
enable INT or DAV using Bit 15 in Control Register 1 and Bit 13
in Control Register 3. The host can then enter sleep mode to
conserve power. The wake-up on-touch feature of the AD7879
is active in this mode; therefore, when the screen is touched,
the programmed sequence of conversions automatically begins.
When the INT or DAV signal asserts, the host reads the new
data available in the AD7879 results registers and returns to
sleep mode. This method can significantly reduce the load on the
host.
Figure 37 shows how the PENIRQ circuit is enabled. The wake-
up on-touch circuit and the PENIRQ circuit are enabled only in
master mode (ADC mode = 11). In slave mode, the PENIRQ /
DAV / INT pin can output only DAV or INT signals.
ON TOUCH
WAKE UP
ENABLE
0
1
CONTROL REGISTER 1
BIT 15
TO THE DIGITAL CORE
PENIRQ/INT/DAV PIN
AD7879