BITBUS Dictionary

BITBUS: Name of one of the world-wide most diffused fieldbuses. Created and developed by Intel in 1983, it was promoted as standard in the 1990 by a special commitee of the IEEE (standard IEEE-1118 1990).

BEUG (Bitbus European Users Group): non-profit organisation devoted to diffuse the BITBUS technology and to organize a basic platform where people using BITBUS can talk to each other and share experiences.

CRC (Cyclic Redundancy Check): a calculated value, based on the contenent of a communication frame, that is insert into the frame itself to enable the check of data consistence after receiving the frame across a network. The BITBUS uses the standard SDLC CRC that is 16 bit wide and will be calculated with the following polynome: X¹⁶ + X¹² + X⁵ + 1 (CCITT compliant).

GSC (Global Serial Channel): On the Intel microcontroller 80C152 the GSC is a serial channel that supports the SDLC protocol. Thanks to this feature, it is possible to realize a BITBUS interface on this chip. Two DMA channels enable the application to serve the GSC in an automatic mode. This ensures a very powerful implementation of the BITBUS protocol on that chip. The other serial channel of the 80C152, called LSC (Local Serial Channel) is equivalent to the standard UART that is present in each 8051-derivated chip.

Frame: Packet of bits that will be transmitted across the network. A frame contains usually a header, the user's data and an end of frame. The frame must contain all the necessary information that enable the two or more partners of the communication to decode the user's data and to ensure that this data is correct.

HDLC (High level Data Link Control): Standard protocol of communication oriented towards message transmission (frames). Basically, the user's data field contained in an HDLC-frame can contain a free number of bits. The SLDC is a subset of the HDLC that defines the whole protocol in more detail and is byte-oriented. That means that a user can place a limited number of bytes in each frame. See also SDLC.

IEEE:Institute of Electrical and Electronics Engineers.
IEEE-1118: The international standard that defines the BITBUS protocol since 1990. The standard can be ordered at the IEEE, with the following description: "1118-1990 IEEE Standard Microcontroller System Serial Control Bus", 272 pages, [1-55937-096-3] [SH13995-NYF] $98.00.

LSC: Local Serial Channel: the LSC is the other serial channel of the 80C152 (see GSC). It is equivalent to the standard UART that is present in each 8051-derivated chip.

Master: On a network, this is the interface that decides about all communication traffic. Usually the master of a network polls every slave to check if they have something to transmit. In a master-slave configuration, only the active master can place a message on the bus. The slave can reply only if it receives a frame from the master that contains a logical token that explicitely enables the slave to reply.

RAC (Remote Access and Control): If reduced to the OSI model, the RAC set of functions is layer 7 (application layer) of the BITBUS. The Remote Access and Control functions enable a basic access to a slave node, without need to write any software or applications else but the communication firmware on the slave. As BITBUS was standardized, the RAC functions got a new name: GBS (Global Bus Services). The GBS cover all the RAC and define some new functions, like the Suspend and Resume Task, and so on. Intel defined 19 RAC functions. The IEEE-1118 standard expanded them to 28 services. Thanks to the new GBS serviceDefine service it is now possible to define new user specific GBS services on a remote node.

SDLC (Serial Data Link Control): Subset of the HDLC used in a large number of communication systems like Ethernet, ISDN, BITBUS, and other. This protocol defines the structure of the frames and the values of a number of specific fields in these frames.

Slave: On a master-slave configured network, there is usually one master and several slaves. The slaves are nodes of the network that can transmit information to the master only when they are polled (called) from it. The rest of the time a slave does not transmit anything.