EVAL-AD7877EBZ Analog Devices Inc, EVAL-AD7877EBZ Datasheet - Page 10

• Manufacturer Part Number: EVAL-AD7877EBZ
• Description: BOARD EVALUATION FOR AD7877
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7877EBZ

• Main Purpose: Interface, Touch Screen Controller
• Embedded: No
• Utilized Ic / Part: AD7877
• Primary Attributes: 4-Wire Resistive Touch Screen Controller, SPI Interface, On-Chip: Temp Sensor, Voltage Reference, 8-Bit DAC
• Secondary Attributes: USB GUI, LCD Noise Reduction Feature, 2.7 ~ 5.25 V, Wake Up on Touch Feature
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

EVAL-AD7877
Configuration
The Configuration button in the Touch Screen window opens
the window displayed in Figure 11. Various parameters can be
changed to alter the configuration of the AD7877. For any
touch screen, a particular set of parameters will yield the best
result for touch screen measurements. The user should experi-
ment with the various parameters to get the best results. The
easy setup configuration is particularly suited to the touch screen
that is included with the evaluation kit.
Conversion Parameters
The Conversion Interval, Acquisition Time, 1st Conversion
Type, and Averaging parameters of the AD7877 can all be
accessed and modified here.
The Conversion Interval sets the timer interval on the AD7877.
The user can set this interval to be 8.19 ms, 1.024 ms, and
512 s, or it can set the AD7877 to convert once (single interval).
The user can turn the AD7877’s averaging function off, or it
can set the device to perform 4, 8, or 16 averages on each
measurement.
The 1st Conversion Delay, which is necessary to allow the
touch screen to settle, can be chosen by the user. The options
for the 1st Conversion Delay are 500 ns, 128 s, 1.024 ms, or
8.19 ms.
The Acquisition Time for each conversion can be chosen to be
2 s, 4 s, 8 s, or 16 s.
There are two choices for Conversion Type: single or differential.
For more information on choosing the conversion parameters,
see the AD7877 data sheet.
Figure 11. Configuration Window
–10–
Reference Selection
The reference voltage for the AD7877 can be either internal or
external. If the user supplies the part with an external reference
voltage, it is of utmost importance that the external reference
value is specified. If the external reference is not specified, all
measurements read by the software may be in error.
If the internal reference is being used, no other reference may be
tied to the V
ence to V
measurements read by the software to be in error.
STOPACQ Polarity
The STOPACQ input signal polarity can be selected by the
user. It is very important that the user selects the correct polar-
ity for the signal applied to the STOPACQ input of the evaluation
board. If the wrong polarity is selected, the ADC on the AD7877
will stop acquiring data and no new measurements will be made.
The easy setup function sets STOPACQ active high.
REF
REF
, while using the internal reference, may cause all
pin on the AD7877. Tying an external refer-
REV. Sp0