Browse Prior Art Database

Idle Fill for a Code Independent Line Control

IP.com Disclosure Number: IPCOM000083593D
Original Publication Date: 1975-Jun-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Donnan, RA: AUTHOR

Abstract

Many line controls provide idle time fill by inserting a sync character or characters in the data stream, when an underrun condition occurs during the transmission of a message. In a code independent line control system, a fixed idle fill character cannot be utilized unless special provisions are taken to prevent such a character from occurring across character boundaries. Described are the steps necessary to implement such an idle character for a code independent line control system.

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Idle Fill for a Code Independent Line Control

Many line controls provide idle time fill by inserting a sync character or characters in the data stream, when an underrun condition occurs during the transmission of a message. In a code independent line control system, a fixed idle fill character cannot be utilized unless special provisions are taken to prevent such a character from occurring across character boundaries. Described are the steps necessary to implement such an idle character for a code independent line control system.

An eight-bit sequence such as a 1 bit followed by seven 0 bits (10000000) may be used as such an idle character, provided that the pattern will not occur anywhere in a normal data stream except as an idle character. The implementation of such a system requires prevention of the occurrence of this pattern within the message information. Thus, whenever the pattern is found, it may with assurance be discarded as a fill or idle character.

In order to prevent the occurrence of the above pattern, the transmitter must insert a 1 bit following any six contiguous 0 bits within the data stream. Doing so will prevent the occurrence of the seven contiguous 0 bits defining the idle character. In those instances where an idle character is required due to an underrun, the pattern 10000000 may be inserted within the data stream.

With this technique, the receiver if it receives six contiguous 0 bits followed by a 1 bit, will delete the 1 bit and the 0's are accepted as valid data bits. If the seventh bit following the six contiguous 0 bits is a 0 bit, then the seven contiguous 0 bits and the leading 1 bit are deleted since they define an idle or fill character.

If delimiters or flags are used to mark the beginning and end of a message, they must differ from the idle character set forth above and the idle...