AD7879 datasheet(21/36 Pages) AD

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AD7879

Rev. 0 | Page 21 of 36

Table 11. Control Register 2

Address

Name

Data

Bit

Description

Default

Value

0x02

PM[1:0]

15:14

ADC power management.

0x4040

00 = full shutdown, the ADC, oscillator, BIAS, and temperature sensor are all powered down.

01 = analog blocks to be powered down depend on the ADC mode.

If ADC mode is master mode; the ADC, oscillator, BIAS, and temperature sensor are powered

down and must wake up when the user touches the screen.

If ADC mode is slave mode, the ADC and temperature sensor are powered down while not

being used. They wake up automatically when required. The oscillator and BIAS are powered

up because they are needed to measure time. This also applies to the single conversion mode.

10 = ADC, BIAS, the oscillator is powered up continuously, irrespective of ADC mode.

11 = as 01.

GPIO EN

GPIO enable.

0 = AUX/VBAT channel active.

1 = GPIO enabled on AUX/VBAT/GPIO.

GPIO DAT

GPIO data bit.

GPIO DIR

GPIO direction.

0 = output.

1 = input.

GPIO POL

GPIO polarity.

0 = the GPIO pin is active low.

1 = the GPIO pin is active high.

SER/DFR

SER/DFR.

Selects normal (single-ended) or conversion.

0 = ratiometric (differential).

1 = normal (single-ended).

A[1:0]

8:7

ADC averaging.

00 = 2 middle values averaged (1 measurement when median filter does not operate).

01 = 4 middle values averaged.

10 = 8 middle values averaged.

11 = 16 values averaged.

M[1:0]

6:5

Median filter size.

00 = median filter does not operate.

01 = 4 measurements.

10 = 8 measurements.

11 = 16 measurements.

SW/RST

Software reset; digital part is reset when this bit is set.

FCD[3:0]

3:0

ADC first conversion delay1.

Starts at 128 μs and goes all the way to 4.096 ms in steps of 128 μs.

1 This delay occurs before conversion of the X and Y coordinate channels (including Z1 and Z2) to allow for screen settling and before the first conversion to allow the

ADC to power up.

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