AD7889 Analog Devices, AD7889 Datasheet - Page 31

• Manufacturer Part Number: AD7889
• Description: Low Voltage Controller for Touch Screens
• Manufacturer: Analog Devices

Specifications of AD7889

• Resolution (bits): 12bit
• # Chan: 6
• Sample Rate: 105kSPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni Vdd
• Adc Architecture: SAR
• Pkg Type: CSP

SYNCHRONIZING THE AD7879/AD7889 TO THE
HOST CPU
The two methods for synchronizing the AD7879/AD7889 to its
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 should first define a conversion sequence in
Control Register 3, initialize the AD7879/AD7889 in Mode 11,
(END OF CONVERSION SEQUENCE)
(GPIO ALERT/OUT OF LIMITS)
DETECTION
ENABLE
CIRCUIT
PENIRQ
DAV
INT
YES
TOUCH SCREEN TOUCHED
Figure 38. Master Mode Operation
ADC MODE = 11?
MASTER MODE
0
1
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CONTROL REGISTER 3
BIT 13
TOUCH SCREEN TOUCHED
INT/DAV/GPIO ALERT
YES
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/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.
ON TOUCH
WAKE-UP
ENABLE
0
1
CONTROL REGISTER 1
BIT 15
TO THE DIGITAL CORE
PENIRQ/INT/DAV PIN
AD7879/AD7889