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The IBM Bisync Protocol

Bisync is an abbreviation for Binary Synchronous Communication (BSC), a data communication protocol developed by IBM in 1967. It's primary purpose was to link System 360/370 processors with the IBM 2780 and 3780 Remote Job Entry (RJE) terminals. The 2780 was later renamed the 3780 and consisted of a card reader for input, and a printer for output.

IBM Bisync protocol enjoyed widespread use through the 1970s and 1980s. The popularity of the protocol resulted in many cloned variations, such as Burroughs Poll/Select, Unisys Uniscope, Honewell VIP/RLP, and protocol variants from NCR and Tandem. Despite its 30-year service life, Bisync protocol is still found in use today. In fact, many ATM machines use Bisync protocol, or a variation of it.

Bisync is a Character-Oriented Protocol (COP) designed for use over synchronous transmission facilities. Efficiency is gained since no Start and Stop bits are used, as is the case with asynchronous facilities.

Bisync Control Characters

IBM Bisync uses certain control codes as part of it's line protocol. These are summarized below:

Control Sequences

The following diagram depicts the multiple byte sequences used for Bisync protocol control. Note that the actual characters used depend upon whether the ASCII or EBCDIC character language is used.

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