Browse Prior Art Database

Data Rate Selection Technique for an Automotive Serial Interface

IP.com Disclosure Number: IPCOM000062177D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Ballou, RV: AUTHOR [+4]

Abstract

This article describes a method to dynamically adapt a serial interface receiver to inputs of multiple baud rates which are presented by different automobiles. The drawing is a flow chart of the technique disclosed herein. The datastream coming from an automobile over an assembly line data line (ALDL) is at one of several speeds; 80, 160, 8192, or 9600 bits per second. In order to properly receive the data, it is necessary to dynamically interrogate the input data stream and adjust the receiving logic accordingly. In the technique disclosed herein this is done by sampling the time between the start of each data bit, and comparing this to a known synchronization character of at least nine ones which indicates the start of a data frame. The sampling is done at the highest frequency first to ensure data validity.

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Data Rate Selection Technique for an Automotive Serial Interface

This article describes a method to dynamically adapt a serial interface receiver to inputs of multiple baud rates which are presented by different automobiles. The drawing is a flow chart of the technique disclosed herein. The datastream coming from an automobile over an assembly line data line (ALDL) is at one of several speeds; 80, 160, 8192, or 9600 bits per second. In order to properly receive the data, it is necessary to dynamically interrogate the input data stream and adjust the receiving logic accordingly. In the technique disclosed herein this is done by sampling the time between the start of each data bit, and comparing this to a known synchronization character of at least nine ones which indicates the start of a data frame. The sampling is done at the highest frequency first to ensure data validity. If no sync character is found after a predetermined time, the next lower frequency is selected and sampling is started again. If after all frequencies have been selected, no sync character has been found, there is a problem with the communication link or the automobile. - 12.5 milliseconds = 80 bits per second - 6.25 milliseconds = 160 bits per second - 122.07 microseconds = 8192 bits per second - 104.2 microseconds = 9600 bits per second When a match is found, the correct data receiving portion of the microcode is invoked, and a normal data reception is started.

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