Appendix
A-11
A.2 Terminology
1) Fieldbus
Fieldbus is an industrial network system for real-time distributed control. It is a way to connect instruments in
a manufacturing plant. Fieldbus works on a network structure which typically allows daisy-chain, star, ring,
branch, and tree network topologies. Previously, computers were connected using RS-232 (serial
connections) by which only two devices could communicate. This would be the equivalent of the currently
used 4-20 mA communication scheme which requires that each device has its own communication point at
the controller level, while the fieldbus is the equivalent of the current LAN-type connections, which require
only one communication point at the controller level and allow multiple (hundreds) of analog and digital points
to be connected at the same time. This reduces both the length of the cable required and the number of
cables required.
2) Rnet
Fieldbus, as the lowest network to connect control device with relay device has adopted 3 layers among
OSI’s 7 layers. The 3 layers are composed of physical layer configured with H2(1Mbps electric), H1
(31.23Kbbs electric), optic/wireless, etc., data link layer with Scheduled and Circulated Token bus and
application layer in charge of application function where user layer is adopted additionally.
3) Token
It is a right to send data of self-station by access right control over Physical Medium.
4) Manchester Biphase-L
It is a data modulating method used in Rnet. Data is sent as encoded by Manchester-l Code and the data
received as encoded by Manchester is converted as decoded.
5) Master Module
Rnet I/F module to be installed on I/O location of the basic base.
6) Slave Module
Rnet I/F module to be installed on CPU location of the basic base or Smart I/O Rnet.