Bitbus is still out there

Forgotten in some quarters, Bitbus (IEEE 1118), one of the oldest of "fieldbuses" is still out there.


Standard optocouplers based on VDE0884 standard provide optical isolation for M304 Bitbus Controller M-module.

Forgotten in some quarters, Bitbus (IEEE 1118), one of the oldest of "fieldbuses" is still out there. This technology has a following, at least in Europe. Bitbus focuses on moving data blocks among autonomous nodes of a distributed control system, via low-cost wiring and relatively long distances and relatively high speed.

Bitbus ranges over 300 m (984 ft) at 375 kbit/s speed or 1.2 km at 62.5 kbit/s. Higher data rates are possible with newer RS-485 transceivers. Repeaters can substantially increase that range. And no line length penalty exists as for buses based on bit-wise arbitration, according to Bitbus European Users Group e.V. (BEUG), which maintains the communication protocol. The master-slave system uses synchronous data link communication (SDLC), a message-based protocol with automatic error detection. Bitbus works with one twisted-pair and ground for cabling.

Recently, AcQ Inducom (Oss, The Netherlands) has added a Bitbus controller to its standard product lineup, based on customer requests and a software update. M304 Bitbus Controller M-module features an i8044 processor, supplying users with all functions needed to implement a Bitbus master or slave node. Resident firmware includes an extensive Remote Access and Control (RAC) command set, which allows performing specific functions on remote nodes. Other M304 Bitbus Controller features include:

  • Mapped command and status registers;

  • Synchronous Bitbus interconnect at three bit rates up to 2.4 Mbit/s;

  • Optional isolated supply (+12 V dc) provided by the network; and

  • Identification EEPROM.

Bitbus network configuration can easily interconnect up to 250 nodes over a distributed enterprise. Different operating modes are optimized for wide applications ranging from high-speed servo motor control in robotics, to remote environmental controls.

—Frank J. Bartos, executive editor, Control Engineering,

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