AD7879 Просмотр технического описания (PDF) - Analog Devices
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AD7879 Datasheet PDF : 40 Pages
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AD7879/AD7889
SYNCHRONIZING THE AD7879/AD7889 TO THE
HOST CPU
The two methods for synchronizing the AD7879/AD7889 to the
host CPU are slave mode (in which the mode bits are set to 01
or 10) and master mode (in which the mode bits set to 11).
In master mode (ADC mode bits = 11), PENIRQ 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/AD7889 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 must first define a conversion sequence in
Control Register 3, initialize the AD7879/AD7889 in Mode 11,
and enable INT or DAV using Bit 15 in Control Register 1 and
Data Sheet
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/
AD7889 is active in this mode; therefore, when the screen is
touched, the programmed sequence of conversions automatically
begins. When the INT or DAV signal is asserted, the host reads
the new data available in the AD7879/AD7889 result registers and
returns to sleep mode. This method can significantly reduce the
load on the host.
Figure 38 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/INT/DAV
pin can output only INT or DAV signals.
ENABLE
PENIRQ
DETECTION
CIRCUIT
YES
ADC MODE = 11?
MASTER MODE
YES
TOUCH SCREEN TOUCHED
ENABLE
WAKE-UP
ON TOUCH
TO THE DIGITAL CORE
DAV
(END OF CONVERSION SEQUENCE)
INT
(GPIO ALERT/OUT OF LIMITS)
TOUCH SCREEN TOUCHED
0
INT/DAV/GPIO ALERT
1
CONTROL REGISTER 3
BIT 13
Figure 38. Master Mode Operation
0
PENIRQ/INT/DAV PIN
1
CONTROL REGISTER 1
BIT 15
Rev. D | Page 32 of 40
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