AD7879ACPZ-RL Analog Devices Inc, AD7879ACPZ-RL Datasheet - Page 24

• Manufacturer Part Number: AD7879ACPZ-RL
• Description: IC ADC 12BIT CTLR TOUCH 16LFCSP
• Manufacturer: Analog Devices Inc
• Type: Touch Screen Controller: 4-Wire Resistiver

Specifications of AD7879ACPZ-RL

• Resolution (bits): 12 b
• Data Interface: I²C
• Package / Case: 16-LFCSP
• Mounting Type: Surface Mount
• Voltage - Supply: 1.6 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Voltage Supply Source: Single Supply
• Sampling Rate (per Second): 105k
• Sampling Rate: 105kSPS
• Supply Voltage Range - Analog: 1.6V To 3.6V
• Supply Current: 480µA
• Digital Ic Case Style: CSP
• No. Of Pins: 16
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7879
CONTROL REGISTERS
CONTROL REGISTER 1
Control Register 1 (Address 0x01) contains the ADC channel
address and the ADC mode bits. It sets the acquisition time and
the timer. It also contains a bit to disable the pen interrupt.
Control Register 1 should always be the last register programmed
prior to starting conversions. Its power-on default value is
0x0000. To change any parameter after conversion has begun,
the part should first be put into Mode 00. Make the changes;
then reprogram Control Register 1, ensuring that it is always the
last register programmed before conversions begin.
Timer (Control Register 1, Bits[7:0])
The TMR bits in Control Register 1 enable the ADC to repeat-
edly perform a conversion or to perform a conversion sequence
only once or at intervals of 35 μs from 550 μs up to 9.440 ms. In
slave mode, the timer starts as soon as the conversion sequence
is finished. In master mode, the timer starts at the end of a
conversion sequence only if the screen remains touched. If the
touch is released at any stage, then the timer stops. The next
time the screen is touched, a conversion sequence immediately
begins.
Table 16. Control Register 1 Timer Selection
TMR
00000000
00000001
00000010
00000011
…
11111101
11111110
11111111
Acquisition Time (Control Register 1, Bits[9:8])
The ACQ bits in Control Register 1 allow the selection of
acquisition times for the ADC of 2 μs (default), 4 μs, 8 μs,
or 16 μs. The user can program the ADC with an acquisition
time suitable for the type of signal being sampled. For example,
signals with large RC time constants can require longer acquisi-
tion times.
Table 17. Acquisition Time Selection
ACQ1
0
0
1
1
ACQ0
0
1
0
1
Function
Convert one time only (default)
Every 550 μs
Every 585 μs
Every 620 μs
…
Every 9.370 ms
Every 9.405 ms
Every 9.440 ms
15
PENIRQ
DIS
Function
4 clock periods (2 μs)
8 clock periods (4 μs)
16 clock periods (8 μs)
32 clock periods (16 μs)
CHNL
ADD2
CHNL
ADD1
CHNL
ADD0
MODE1
ADC
MODE0
ADC
Figure 29. Control Register 1
ACQ1 ACQ0 TMR7 TMR6 TMR5 TMR4 TMR3 TMR2 TMR1 TMR0
Rev. 0 | Page 24 of 36
ADC Mode (Control Register 1, Bits[11:10])
The mode bits select the operating mode of the ADC. The
AD7879 has three operating modes. These are selected by
writing to the mode bits in Control Register 1. If the mode
bits are 00, no conversion is performed.
Table 18. Control Register 1 Mode Selection
ADC
MODE1
0
0
1
1
If the mode bits are 01, a single conversion is performed on
the channel selected by writing to the channel bits of Control
Register 1 (Bit 12 to Bit 14). At the end of the conversion, if the
TMR bits in Control Register 1 are set to 00000000, the mode
bits revert to 00 and the ADC returns to no convert mode until
a new conversion is initiated by the host. Setting the TMR bits
to a value other than 00000000 causes the conversion to be
repeated.
The AD7879 can also be programmed to automatically convert
a sequence of selected channels. The two modes for this type of
conversion are slave mode and master mode.
For slave mode operation, the channels to be digitized are selected
by setting the corresponding bits in Control Register 3. Conver-
sion is initiated by writing 10b to the mode bits of Control
Register 1. The ADC then digitizes the selected channels and
stores the results in the corresponding results registers. At the
end of the conversion, if the TMR bits in Control Register 1 are
set to 00000000, the mode bits revert to 00 and the ADC returns
to no convert mode until a new conversion is initiated by the
host. Setting the TMR bits to a code other than 00000000 causes
the conversion sequence to be repeated.
For master mode operation, the channels to be digitized are
written to the 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, conver-
sion does not immediately begin. The AD7879 waits 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. The AD7879 waits for the
screen to be touched again, or for a timer event if the screen
remains touched, before beginning another sequence of
conversions.
ADC
MODE0
0
1
0
1
Function
Do not convert (default)
Single-channel conversion; the AD7879 is
in slave mode
Sequence 0; the AD7879 is in slave mode
Sequence 1; the AD7879 is in master mode
0