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  • LV Digital Comm display tagshide tags

    This module is included inLens: Analog / Digital Communications with National Instruments LabVIEW
    By: Sam ShearmanAs a part of collections:"SubVI Specifications for "Communication Systems Projects with LabVIEW"", "Communication Systems Projects with LabVIEW"

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    ""Communication Systems Projects with LabVIEW" features ten projects that draw upon a library of over 40 subVIs constructed as part of the project activities. Each module in this manual completely […]"

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cid_DetectStartBit.vi

Module by: Ed Doering. E-mail the author

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Summary: Build a LabVIEW subVI to detect the first start bit in the Caller ID message bitstream.

Table 1
LabVIEWtop.png This module refers to LabVIEW, a software development environment that features a graphical programming language. Please see the LabVIEW QuickStart Guide module for tutorials and documentation that will help you:
• Apply LabVIEW to Audio Signal Processing
• Get started with LabVIEW
• Obtain a fully-functional evaluation edition of LabVIEW

Note:

Visit LabVIEW Setup to learn how to adjust your own LabVIEW environment to match the settings used by the LabVIEW screencast video(s) in this module. Click the "Fullscreen" button at the lower right corner of the video player if the video does not fit properly within your browser window.

LabVIEW SubVI: cid_DetectStartBit.vi

  • Description: Detect the first start bit in the Caller ID message bitstream, and return only the remaining bits in the bitstream. The Caller ID message consists of three distinct regions: (1) channel seizure (alternating pattern of T and F values), (2) steady mark (constant T values), and (3) data block containing the message payload. This subVI detects the steady mark region and then identifies the array index (time point) at which the input bitstream first changes to F.
  • Category: Caller ID decoding ("cid" prefix)

Inputs (Controls)

  1. bitstream in -- 1-D Boolean array

Parentheses ( ) indicate default value; square brackets [ ] designate units.

Outputs (Indicators)

  1. datablock bitstream -- 1-D Boolean array
  2. start bit index -- I32

Required Behavior

  • The bitstream in input should contain a complete Caller ID message bitstream as generated by other demodulating and bit synchronization and sampling subsystems.
  • The datablock bitstream output contains only the data block portion of the input bitstream, beginning with the first start bit of the first character, i.e., the first frame. If no data block is detected then datablock bitstream will return empty.
  • start bit index is the index (location) of the data block detected in the input message. If no data block is detected then start bit index will return -1.

LabVIEW Coding Tips

View the screencast video in Create a SubVI in LabVIEW to learn the mechanics of subVIs.

Refer to the Figure 1 screencast video for LabVIEW coding tips and techniques specific to this subVI.

Figure 1: [video] LabVIEW coding tips and techniques for cid_DetectStartBit.vi
Figure 1 (subVI_cid_DetectStartBit-vi.htm)

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