Distributed Control Modules
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?
- The BITBUS hardware and software architecture was developed by the OEM Modules Operation
of Intel* Corporation during 1982 and 1983.
- The first products were launched in February of 1984. They were:
- iSBX* 344 -- daughter card (typically master) for mounting on Multibus SBC's (Single
- iRCB* 44/10 -- remote controller board (typically slave) digital I/O points 3U Eurocard
- iDCX* 51 -- Real Time operating system for the Intel 8051 family microcontrollers
- iDCM* 44 -- preconfigured iDCX 51 task allowing easy digital I/O programming
- iRMX* 510 -- SDK (Software Development Kit) for host operating systems run on SBC's
- BITBUS was approved as IEEE standard 1118 during 1984.
- Additional BITBUS products launched by Intel were:
- iRCB 44/20 -- remote controller board (typically slave) analog I/O points 3U Eurocard
- iRCX* 910 -- digital I/O point conditioning/wiring rack-mount panel
- iRCX 920 -- analog I/O point conditioning/wiring rack-mount panel
- iPCX* 344 -- ISA adapter card for PC-compatibles (typically master)
- iDCS* 100 -- (also known as the BITBUS Toolbox) expanded SDK
- iDCS 101 -- source code to SDK interface libraries, in C language
- BITBUS Starter Kit -- teaching / orientation tool
- Due to financial considerations, Intel decided to discontinue development and support of
the BITBUS product line in 1988.
- In 1990, the BITBUS software was placed by Intel into the public domain so that existing
users, hobbyists, and academic institutions could continue to benefit from the technology.
- In 2000, I finally got around to creating this web site. You can get some information
and download some of the software from here.
What are the Features of the iDCX 51 real time operating system?
- Runs on Intel 8051 family microcontrollers. It had been tested on the 8051, 8044, 80152,
80252, and 80452.
- Multitasking real time operating system. Up to 8 concurrent tasks. If the iDCM 44 Remote
Access and Control task is configured, that counts as Task 0 of tasks 0 through 7.
- Very compact. It's written in 8051 assembler and fits in 2.2 kB.
- Supports interprocess communication, both between on-board tasks, and from on-board
tasks to host application software connected to the master module.
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:
- dcx51.zip, 603 kB -- ZIP archive of iDCX 51 materials (the OS)
- dcm44.zip, 433 kB -- ZIP archive of iDCM 44 materials (the
- dcs101.zip, 99 kB -- ZIP archive of iDCS 101 materials (host
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 alfirin.net" (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 http://www.alfirin.net/flamer/ 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, ....
- The 8044 is now being produced by Rochester Electronics, http://www.rocelec.com.
- Boards are being produced by various manufacturers. Check out InBus Engineering, http://www.inbus.com for a great
- For some reason, BITBUS still seems to be very popular in Europe, check out the BITBUS
European User's Group at http://www.bitbus.org.
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!
Thanks go to Pieter Hoeben of Hoeben Electronics, http://www.hoeben.com,
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.