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Revision: August 30, 2011
Note: This document applies to REV A of the board.
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Doc: 502-217 page 1 of 2
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Overview
The PmodAD2 is an analog-to-digital converter
module with up to four channels at 12-bit
resolution powered by the Analog Devices
AD7991.
Features include:
• up to four analog to digital converter
channels
• up to 12-bit resolution
• on-board 2.048V voltage reference
• ability to choose the voltage reference
• I
2
C interface
Functional Description
The PmodAD2 uses an 8-pin connector that
allows communication via I
2
C. The PmodAD2
also has a 6-pin connector that allows up to
four analog inputs or up to three analog inputs
and a voltage reference.
Interface
All communications with the device must
specify a device address and a flag indicating
whether the communication is a read or a
write. This is followed by the actual data
transfer. For details on read and write
procedures please see the AD7991 datasheet.
Device configuration is performed by writing to
the configuration register within the device.
This allows you to choose which channels are
converting data, whether or not there is an
external reference voltage, and whether or not
there is bit trial or sample delay.
To read data from the conversion result, see
“Reading from the AD7991/AD7995/AD7999”
in the AD7991 datasheet.
The I
2
C interface standard uses two signal
lines. These are I
2
C data (SDA) and I
2
C clock
(SCL). These signals map to the serial data
(SDA) and serial clock (SCL), respectively, on
the AD7991.
Connector J1 – I2C Communications
Pin Signal Description
1, 2 SCL I2C Clock
3, 4 SDA I2C Data
5, 6 GND Power Supply Ground
7, 8 VCC Power Supply (3.3V)
Interface Connector Signal Description
PmodAD2 Reference Manual
www.digilentinc.com page 2 of 2
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Analog Inputs and V
Ref
The PmodAD2 allows for up to four analog
inputs, VIN1 – VIN4. To use the input VIN4,
the jumper JP1 must be set to V4.
The configuration register has a REF_SEL bit
that, when enabled, allows a voltage other than
the supply voltage to be used as the reference.
If REF_SEL is enabled, and if JP1 is set to
REF, V
Ref
from the on-board voltage reference
generator is 2.048V. If JP1 is set to V4, V
Ref
is
the voltage at input VIN4.
Connector J2 – Analog Input
Pin Signal Description
1 VIN1 Analog Input 1
2 VIN2 Analog Input 2
3 VIN3 Analog Input 3
4 VIN4 Analog Input 4
5 GND Power Supply Ground
6 VCC Power Supply (3.3V)
