Monday, August 22, 2011

Communication ARCNET on ABB Scalable PLC





Attached Resource Computer NETwork (ARCNET) is a multi-purpose, open field bus solution with instantaneous ability. It can be utilized for programming the controller of AC500 and AC31 series and for networking of multi-master, but also for linking additional subscribers of ARCNET, e.g. PCs through a suitable interface card.

Topology
ARCNET is one of the not many networks that can be worked in every imaginable topology. Options comprise star, tree topologies, or bus, or combinations of these. This means that ARCNET can be utilized for a wide different applications field.

Assignments of Bus
ARCNET runs on the procedure of token-passing, where every subscriber has the same rights.

Configuration Mechanisms
ARCNET permits to put in and to remove subscribers from the network during runtime. The whole network will be reconfigured when a new subscriber is included.

Mechanisms of Security
A CRC of 16-bit is attached to each data packet, and verified by the recipient. If the token is lost, a routine of reconfiguration will be started, and the network will be reorganized automatically.

Characteristics Physically
For direct connection to the CPU, ABB advises cables coaxial as medium of transmission. But fiber-optic cables or also a pair of twisted cables are able to be linked through converters of bus. The lengths of line which can be reached without any amplifiers transitional are not only on the old medium, however also on a chosen baud rate and the subscriber numbers. The segment differs from around 120 m for a simple bus of two-wire, up to 3 km use fiber-optics. The different transmission topologies can be joint with every other and the length of transmission can be enlarged by providing suitable hubs. The cables of coaxial used are a 93 Ohm type, e.g. RG 62. The allowed cables of twisted-pair are specific in IEEE 802.3i-1990. At 2.5 MBit/s and with cables coaxial, such as, the bus segment maximum length is 300 m without a hub and with eight subscribers. The maximum transmission distance end to end depends on the connected subscribers number. A maximum of 16 km can be reached with twisted-pair cables about 6 km, in each case at 2.5 MBit/s with cables coaxial. The link of fiber-optic offers the highest interference immunity degree. Spaces of up to 3 km are probable at 2.5 MBit/s with fiber-optics glass; with cables of plastic fiber-optic only small distances of up to around 100 m. The baud rate engages in recreation no important role in cable transmission of fiber-optic.


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