Distributed Control Modules
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What is BITBUS?

BITBUS is a serial interconnect for distributed control modules.

Serial means it sends data down the interconnect cable one bit after another. The 9-conductor interconnect cable consists of a differential data pair, a differential clock pair, and signal grounds. The clock speeds supported are self-clocked mode (crystal provided) at 62.5 kb/s and 375 kb/s and synchronous mode (you supply the crystal) from 500 kb/s to 2.4 Mb/s. Conductors are also reserved for low voltage power (+12V) and chassis ground. The electical transmission standard used is RS-485, which is a variant of synchronous RS-232. The datalink protocol is SDLC (Synchronous Data Link Control) developed by IBM.* SDLC requires that one module be designated as the master and all other modules respond as slaves.

Distributed means that the multiple controllers attached to the BITBUS can be physically distant from one another. The SDLC protocol allows up to 250 controllers to be daisy-chained up to a maximum of 13.2 km. Distance is inversely dependent upon clock speed (the farther you go, the slower it has to be).

Control Modules means small microprocessor-based digital and/or analog I/O cards, designed for the purpose of controlling mechanical equipment, e.g., the typical application is the management of a conveyor assembly line. Control module printed circuit boards are 3U high (100 mm) and 220 mm deep Eurocard DIN rack-mount form factor.

What is the History of BITBUS?

What are the Features of the iDCX 51 real time operating system?

Can I still get BITBUS software?

Yes. Much of the BITBUS software was saved for posterity by me. Some of the popular software can be downloaded from this web site:

If there are sufficient requests, I will make additional downloads available.

Also, I have a CD-ROM containing approximatley 50 MB of software that I can duplicate for you. Contact me by e-mail at "flamer at" (change the word "at" to a real "@" sign) or drop me a letter, and let me know what you want. Go see my personal web page at to find my current Snail-mail address.

Can I still get BITBUS hardware?

Yes.  Intel discontinued manufacture of the 8044 BEM (BITBUS Enhanced Microcontroller, a variant of the 8051 with the iDCX 51 operating system and the iDCM 44 I/O task fabricated in masked ROM), boards, and software. However, ....

Can I still get BITBUS documentation?

Intel Technical Publications discontinued production of BITBUS user manuals. Some documentation is available on the CD-ROM, most notably the iDCX 51 user's manual.

I hope this helps all you BITBUS die-hards still out there!

--Jim Trethewey

Thanks go to Pieter Hoeben of Hoeben Electronics,, for information on European activities.

* Trademarks and brands are the property of their respective owners.

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Last updated: Sat Jan 22 2005 1:03 PM PST.