AD7879 datasheet(25/36 Pages) AD

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AD7879

Rev. 0 | Page 25 of 36

ADC Channel (Control Register 1 Bits[14:12])

The ADC channel 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 19.

For Mode 0 (single-channel) conversion, the channel is selected

by writing the appropriate CHNL ADD2 to CHNL ADD0 code

to Control Register 1.

For sequential channel conversion, channels to be converted are

selected by setting bits corresponding to the channel number in

the Control Register 3 for slave and master mode sequencing.

For both single-channel and sequential conversion, a normal

conversion (single-ended) is selected by clearing the SER/DFR

bit in Control Register 2 (Bit 9). Ratiometric (differential)

conversion is selected by setting the SER/DFR bit.

PENIRQ Enable (Control Register 1, Bit 15)

The AD7879 has 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 is working as a pen interrupt and it goes low whenever the

screen is touched. When the pen interrupt enable bit is set to 1,

the pin interrupt request is disabled and the pin functions as INT.

Table 19. 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

1 1 1

X+ (Y position)

Off

Y+

Y−

1 1 0

Y+ (X position)

Off

X+

X−

1 0 1

X+ (Z1 touch pressure)

X+ off, X− on

Y+ on, Y− off

Y+

X−

1 0 0

Y− (Z2 touch pressure)

X+ off, X− on

Y+ on, Y− off

Y+

X−

0 1 1

AUX

Off

VCC

GND

0 1 0

VBAT

Off

VCC

GND

0 0 1

TEMP

Off

VCC

GND

0 0 0

Invalid address