Technical Guide P92x/EN CT/E11
Courier Database
MiCOM P921-P922-P923 Page 69/118
2. K-BUS PROTOCOL AND COURIER LANGUAGE
The serial communications are transmitted on K-Bus, a multi –drop network
proposing an instantaneous interface with the IEC 870-5 FT1.2 standards. The
language and the communication protocol used are Courier. this concept permits
especially to the generic programs of the principal units to access to a high number
of different relays without need to change permanently the principal unit program for
each relay type. The relays form a distributed database in which the principal
workstation proceeds to a selective call of the slave relays in order to know all
necessary information.
Courier is designed to work using a selective call feature which forbids any slave
periphery to communicate directly with the central unit when a particular information
about an event needs to be transmitted. The slave workstation has to wait that the
principal workstation asks for the information. With Courier protocol, each
information is given into a box with a code of the length and the database type. By
knowing the database format, the reception periphery can read them.
2.1 K-BUS
K-Bus is a communication system developed for connecting the slave peripheries to
the central unit, permitting them to execute all remote monitoring and remote control
functions using the appropriate communication language. K-Bus is not able to
permit a direct communication between the slave peripheries. Only a communication
between the central unit and the slave peripheries can be established. The principal
characteristics of the K-Bus are the profitability, high security level, his installation
facility and his user friendliness.
2.1.1 K-Bus Transmission Layer
The communication port RS485 is based on several levels of reception and
transmission voltages with galvanic isolation given by a transformer. A selective call
protocol is used. No relay unit is allowed to transmit before having received a
validation message without any error detection. The transmission is synchronous on
a pair of isolated waves. The data are coded FM0 with a clock signal to eliminate all
CC-component, allowing the signal to cross the transformers.
With the exception of the central units, each network node is passive. The defective
units can not interfere with the communication established with the other healthy
units. The message format is HDLC. The data transmission speed is 64 Kbits/s.
2.1.2 K-Bus Connection
The connection on the K-Bus port is realized by screwed terminals of 4 mm of MIDOS
standards or by FASTON-connectors. A cabled pair is sufficient to realize the
connection, Knowing that the polarity is not important. It is recommended to use an
external screen earth linked at the end of the principal workstation only. The screen
has to be fixed with a M4 screw following the wiring scheme. The functioning of the
K-BUS network is guaranteed for 32 units connected on 1000 meters of cables.
Thanks to the data code method, the polarity of the Bus cable connection is not
important.
Note : the K-Bus network has to finish with a 150 ohms resistance on
each end of the bus. The principal workstation can be placed
anywhere on the network. This command point has to be
unique.
To Next Page
Loading...
