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Table of Contents

Introduction

Connecting to the 24/7 Data Acquisition Module

Hardware

On-Board Reference

Digital Inputs

Analog Inputs

Programmable Gain

Input Protection

Allowable Input Impedance

Converter Noise and Effective Resolution

Other Sources of Noise and Offset Error

Tips For Measuring Small Voltages

Addressing the 24/7 WildCard Using Module Select Jumpers

Software

Initializing the 24/7 Data Acquisition Wildcard

Specifying the Reference Voltage

Starting a Conversion

Calibration Options
Choosing the Sample Rate
Setting the Gain
Choosing Bipolar or Unipolar Conversion
Specifying 16- or 24-bit Resolution
Synchronizing Conversions
Specifying the Source Channels

Obtaining A Sample

Single- and Multi-Channel Sampling

Continuous Sampling from a Single Channel
Sequential Sampling from Several Channels

C Example Listing (pdf)

Forth Example Listing (pdf)

Glossary

Appendix A:24/7 Data Acquisition Wildcard Pin-outs

Appendix B:24/7 Data Acquisition Wildcard Schematics (pdf)

24/7 Data Acquisition Wildcard Users Guide

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Software

The following section describes the high-level software routines that initialize, calibrate, configure, and command the 24/7 Data Acquisition Wildcard. Once the 24/7 Data Acquisition Wildcard is commanded to start converting, it continually samples and converts at a fixed rate. You can read the output once or store each sequential conversion to a memory buffer. Only one channel is sampled at a time; selecting a new channel requires restarting a conversion.

The software routines use global variables to store the current module and channel information. Thus all of the 24/7 Data Acquisition Wildcard software routines are non-re-entrant and only a single task in a multitasking application can use a 24/7 Data Acquisition Wildcard.

Please take time to read through the example programs. The examples illustrate how to effectively use the pre-coded software drivers. Many subtleties involved with using the 24/7 Data Acquisition Wildcard are highlighted in the example code.

The following steps and corresponding routines are required to obtain a sample from the 24/7 Data Acquisition Wildcard:

  1. Initialize the 24/7 Data Acquisition Wildcard using Init_AD24.
  2. Specify the reference voltage by calling Use_Onboard_Ref or Use_External_Ref.
  3. Calibrate, configure, and start converting samples from a channel with Start_Conversion. Start_Conversion will first calibrate the chip using whichever calibration scheme you specify, then continuously sample and convert samples at a fixed rate. Calibration will take several output periods, during which no output is available, after which outputs can be read anytime and will be updated at the fixed output rate.
  4. Fetch one or more samples from the converter chip by executing AD24_Sample or AD24_Multiple. AD24_Sample returns with the most recently acquired sample, and AD24_Multiple stores a series of samples to an array in memory.
  5. You can change channels or sample rate without doing a recalibration by executing Start_Conv_With_Values. It will reset the convertor, delay for three output periods, then update its output each output period at the specified output rate.

Each step is described in detail in the next four sections.

Initializing the 24/7 Data Acquisition Wildcard

To initialize the 24/7 Data Acquisition Wildcard, call Init_AD24. This configures the module for communication via the Mosaic controllerís Serial Peripheral Interface (SPI), starts the controllerís Timeslicer, and performs a reset (Reset_AD24) that disconnects all of the analog inputs from the AD7714 and resets its digital filter, analog modulator, and registers.

Specifying the Reference Voltage

Once the module is initialized, you must choose what type of reference voltage to use. To use the on-board 2.5 V reference voltage, simply call Use_Onboard_Ref and make sure the jumper shunt on J1 is not installed. If an external reference voltage is required, connect the reference voltage to FDREF+ (pin 9 on H2) and FDREF- (pin 11 on H2) and call Use_External_Ref. These two routines connect the specified reference voltage to the reference input on the analog to digital converter. Be sure to only use 1.0 to 2.5 volts as an external reference voltage and be sure that FDREF+ is more positive with respect to FDREF-.

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