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TECHNIQUE FOR IMPLEMENTING A DIGITAL COMMUNICATIONS LINK FOR DIAGNOSTICS

IP.com Disclosure Number: IPCOM000006238D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2001-Dec-17
Document File: 2 page(s) / 124K

Publishing Venue

Motorola

Related People

Walt Anderson: AUTHOR [+2]

Abstract

There are many digital communication systems where it is desirable to provide a flexible static and run-time digital diagnostic capability in the transmit path without increasing the digital data bandwidth or data rate required. This technique addresses this need by embedding digital diagnostic data into the primary digital transmit path. The diagnostic data is selec- tively embedded in a manner that requires no addi- tional data bandwidth or data rate, and avoids inter- rupting or causing prohibitive distortion in the primary digital transmit stream.

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MOTOROLA INC. Technical Developments Volume 13

July 1991

TECHNIQUE FOR IMPLEMENTING A DIGITAL COMMUNICATIONS LINK FOR DIAGNOSTICS

by Walt Anderson, Gary Fatt

I. ABSTRACT

  There are many digital communication systems where it is desirable to provide a flexible static and run-time digital diagnostic capability in the transmit path without increasing the digital data bandwidth or data rate required. This technique addresses this need by embedding digital diagnostic data into the primary digital transmit path. The diagnostic data is selec- tively embedded in a manner that requires no addi- tional data bandwidth or data rate, and avoids inter- rupting or causing prohibitive distortion in the primary digital transmit stream.

II. DESCRIPTION

  This technique provides a serial diagnostic com- munications path between digital devices by inserting digital diagnostic information into a primary informa- tion bearing digitized data stream. It has been imple- mented in the digital radio architecture shown in fig- ure 1. In this application, the DSP based Digital Modulator converts transmit information into a digi- tized signal and filters the signal using digital filtering techniques. These digitally filtered, 16 bit linear sam- ples are sent to a digital-to-analog convertor to pro-

duce the analog transmit signal. The digital diagnostic information is embedded in the 16 bit digital sample stream. In this way, the DSP Based Digital Modulator uses the digitized data stream to report error messages, synchronization and status information while simulta- neously transmitting the primary information. Note that this eliminates the need for a separate dedicated diagnostics communication path from the DSP Based Digital Modulator.

A. EMBEDDED MESSAGE FORMAT

  As previously mentioned, the digital diagnostic message is embedded in the i6 bit digital sample. The embedded message can vary in length from 1 to 15 bits. The message always occupies .the least signifi-

0 Motorola. 1°C. 1991

cant bits-when the message length is less than or equal to 15 bits. The most significant bit of the digitized data is left unaltered to avoid changing the sign of the value represented by the 16 bit digital sample.

  While there are many possible formats for the embedded message, the implementation we have cho- sen is shown in figure 2 below. In this format, the 4 most significant bits are always preserved as the cur- rent transmit sample, up to 8 bits can be dedicated to the diagnostic data or left unaltered, and the 4 least significant bits of the message are dedicated to a diag- nostic message opcode. When a transmission is in progress, any bits not specifically required by the embedded message are dedicated to the current trans-

mit sample.

  When there is an embedded message present the message recipient must be alerted to this fact. In our application, a digital control line is asserted by the DSP Based Digital Modulator. Otherwise, there is no embedded message present and the t...