EVAL-AD7879EBZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7879EBZ' PDF : 36 Pages View PDF
Data Sheet
For master mode operation, the channels to be digitized are
written to Control Register 3. Master mode is then selected by
writing 11 to the mode bits in Control Register 1. In this mode,
the wake-up on touch feature is active; therefore, conversion
does not begin immediately. The AD7879/AD7889 wait until
the screen is touched before beginning the sequence of conversions.
The ADC then digitizes the selected channels, and the results are
written to the result registers. Before beginning another sequence
of conversions, the AD7879/AD7889 wait for the screen to be
touched again or for a timer event if the screen remains touched.
ADC Channel (Control Register 1, Bits[14:12])
The ADC channel address is selected by Bits[14:12] of Control
Register 1 (CHNL ADD2 to CHNL ADD0). A complete list of
channel addresses is given in Table 21.
For single-channel conversion, the channel address is selected
by writing the appropriate code to the CHNL ADD2 to CHNL
ADD0 bits in Control Register 1.
AD7879/AD7889
For sequential channel conversion, the channels to be converted
are selected by setting the bits corresponding to the channel
number in Control Register 3 for slave and master mode
sequencing.
For both single-channel and sequential conversion, a normal
conversion (single-ended) is selected by setting the SER/DFR bit in
Control Register 2 (Bit 9). Ratiometric (differential) conversion
is selected by clearing the SER/DFR bit.
PENIRQ Enable (Control Register 1, Bit 15)
The AD7879/AD7889 have a dual function output that performs
as PENIRQ or INT, depending on the pen interrupt enable bit
(Bit 15 of Control Register 1). When this bit is set to 0, the pin
functions as a pen interrupt and goes low whenever the screen
is touched. When the pen interrupt enable bit is set to 1, the pen
interrupt request is disabled and the pin functions as an interrupt
when a measurement exceeds a preprogrammed limit (INT).
Table 21. Codes for Selecting Input Channel and Normal or Ratiometric Conversion
Channel SER/DFR CHNL ADD[2:0] Analog Input
X Switches
Y Switches
0
0
111
X+ (Y position)
Off
On
1
0
110
Y+ (X position)
On
Off
2
0
101
X+ (Z1 touch pressure) X+ off, X− on
Y+ on, Y− off
3
0
100
Y− (Z2 touch pressure) X+ off, X− on
Y+ on, Y− off
4
0
011
AUX
Off
Off
5
0
010
VBAT
Off
Off
6
0
001
TEMP
Off
Off
0
000
Invalid address
7
1
111
X+ (Y position)
Off
On
8
1
110
Y+ (X position)
On
Off
9
1
101
X+ (Z1 touch pressure) Off
Off
12
1
100
Y− (Z2 touch pressure) Off
Off
13
1
011
AUX
Off
Off
14
1
010
VBAT
Off
Off
15
1
001
TEMP
Off
Off
1
000
Invalid address
REF+
Y+
X+
Y+
Y+
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
VCC
REF−
Y−
X−
X−
X−
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
Rev. D | Page 27 of 40
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