ad7879-1acbz-rl Analog Devices, Inc., ad7879-1acbz-rl Datasheet - Page 26

• Manufacturer Part Number: ad7879-1acbz-rl
• Description: Low Voltage Controller For Touch Screens
• Manufacturer: Analog Devices, Inc.

AD7879
CONTROL REGISTER 2
Control Register 2 (Address 0x02) contains the power
management bits, the GPIO settings, the SER/ DFR bit
(to choose single or differential methods of touch screen
measurement), the averaging and median filter settings, a bit
that allows resetting the part, and the first conversion delay
bits. Its power-on default value is 0x4040. See the
Register Descriptions
control registers.
First Conversion Delay (Control Register 2, Bits[3:0])
The first conversion delay (FCD) bits in Control Register 2
program a delay from 128 μs (default) up to 4.096 ms before
the first conversion to allow the ADC time to power up. This
delay also occurs before conversion of the X and Y coordinate
channels to allow extra time for screen settling, and after the
last conversion in a sequence to precharge PENIRQ .
Table 20. First Conversion Delay Selection
FCD
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1.024 ms
1.152 ms
1.280 ms
1.536 ms
1.792 ms
2.048 ms
2.560 ms
3.584 ms
4.096 ms
Function
128 μs
256 μs
384 μs
512 μs
640 μs
768 μs
896 μs
section for more information on the
15
PM1
PM0
GPIO
EN
GPIO
DAT
GPIO
DIR
Detailed
GPIO
POL
Figure 30. Control Register 2
SER/
DFR
Rev. 0 | Page 26 of 36
AVG1 AVG0 MED1 MED0
Power Management (Control Register 2, Bits[15:14])
The power management (PM) bits in Control Register 2 allow
the power management features of the ADC to be programmed.
If the PM bits are 00, the ADC is permanently powered down.
This overrides any setting of the mode bits in Control Register 1.
If the PM bits are 01, both the ADC and the reference power
down when the ADC is not converting. If the PM bits are 10 or
11, the analog blocks to be powered down depend on the ADC
mode settings. Power management overrides the ADC modes.
Table 21. Power Management Selection
PM1
0
0
1
1
PM0
0
1
0
1
SW/
RST
Function
Full shutdown; ADC, oscillator, BIAS, and
temperature sensor are all turned off. The only
way of coming out of this mode is to write to the
part over the serial interface and change the PM
bits. This setting overrides any other setting on
the part, including the ADC mode bits.
The analog blocks to be powered down depend
on the ADC mode settings. If the ADC mode is set
to master mode, the ADC, BIAS, temperature
sensor, and oscillator are powered down and
must wake up when the user touches the screen.
If the ADC mode is set to slave mode, the ADC
and the TEMP 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.
ADC, BIAS, and the oscillator are powered up
continuously irrespective of ADC mode.
As 01.
FCD3 FCD2 FCD1 FCD0
0