Datasheet

AD7879/AD7889
Rev. C | Page 27 of 40
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.
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 REF+ REF−
0 0 111 X+ (Y position) Off On Y+ Y−
1 0 110 Y+ (X position) On Off X+ X−
2 0 101 X+ (Z1 touch pressure) X+ off, X− on Y+ on, Y− off Y+ X−
3 0 100 Y− (Z2 touch pressure) X+ off, X− on Y+ on, Y− off Y+ X−
4 0 011 AUX Off Off V
CC
GND
5 0 010 VBAT Off Off V
CC
GND
6 0 001 TEMP Off Off V
CC
GND
0 000 Invalid address
7 1 111 X+ (Y position) Off On V
CC
GND
8 1 110 Y+ (X position) On Off V
CC
GND
9 1 101 X+ (Z1 touch pressure) Off Off V
CC
GND
12 1 100 Y− (Z2 touch pressure) Off Off V
CC
GND
13 1 011 AUX Off Off V
CC
GND
14 1 010 VBAT Off Off V
CC
GND
15 1 001 TEMP Off Off V
CC
GND
1 000 Invalid address