Mode of operation
Siemens PLT130
.
1994
2/3
Addressing, transmission modes
This method has the following impor tant advantages:
There is far less loading on the bus system sinceonly the
informationis read from theautomation system whichis cur-
rently displayed on the monitor channels
Data need only be stored at one position as a result of the
distributed data base principl e. Modifications are therefore
only necessary at one position
No special planning for the OS systems is requiredin the
automationsystems (exception:curve display)
Acces to information in the aut omation systems by another
computer is possible without additional planning (by using t he
function ”Read parameters”) .
The cyclic data exchange is also used for a life test of all par tici-
pants connected to the CS 275 bus by an OS operati on and
monitoringsystem. Each failure andalso the return of a partici-
pant is supervised and signal led.
Sporadic data transfer
Sporadic data transfer is neces sary to rapidly pass on m odifica-
tions in the process control system to other participants.Typical
examples are faults or changes in status (e. g. motor on/off)
whichdetects the automationsystem. Messages exchanged
betweenseveral automationsystems are transmitted by means
of the coupling blocks MKS/MKE.
A status word is assi gned to each function block for processing
with standardized operation and monitor ing as well as to driver
blocks for I/O modules wit h standardized display. The changes
in signal are detected event-controll ed by the status word or by
the MKS block, provided with the actual t ime (MKS only) and
transferredto the bus system. This then transfers MKSmes-
sagesto a maximum of 6 participants(typically OS systems
and higher-level computers) which have ” registered” them-
selvesfor this information when thecomplete system was
started up. This presents the advantage that the automati on
systemneed onl y transmit one message with one or several
destination addresses. In addi tion, only those stations receiv e
the information which actuall y require it.
Datatransfer with OS systems and computers takesplace using
the functions ”Read parameters ” and ”Write parameters”.
Fig.2/2 Sporadic/acyclic data exchange, example OS/AS and AS/AS
Addressing
The addressing of the participant s of the bus system is oriented
towards the transmissi on of messages between several autono-
mous buses and within a bus.
Eachparticipant is identified by two addresses:
Bus address (0 to 7), i. e. 8 autonomous buses are possible.
7 bus couplers are needed in this case.
Participant address (0 to 99) .
These two addresses are set on the local bus interface module
using jumpers or DIP switches .
The bus coupler behaves like a par ticipant with respect to each
bus. It has an address on each bus.
Transmission modes
A differentation is made between two trans mission modes when
configuring and defining the AKS and BKS transmi tter blocks:
-- Direct coupling (DI)
-- Common data (CD).
Direct coupling (DI)
The registered participants are direct ly addressed by the trans-
mitter blocks, i. e. each partici pant only receives the data which
is assigned for it. Up t o 6 receivers can be registered with a
transmitter block and receiv e the data (analog or binary val ues)
pertaining to it with each t ransmission cycle of this block.
Any participant on the bus can be a receiv er.Transmiss ion can
also take place via bus couplers . A receiver is entered as such
in the transmitter block in the respective automation system.
The MKS block only operates in direct coupling mode.
Common-Data (CD)
The transmitter block s ends the data simultaneously to all con-
nected participants of a par ticular bus. Thus certain i dentical
data can be planned in a transmitter bl ock for many participants
on a bus and many destination addresses can then be reached.
The CD procedure can only be used for subscribers with the
same bus address. Addressing via bus couplers is not possibl e.
The participants on a bus connected v ia a bus coupler can be
addressed via their own CD procedure.
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This catalog is out of date, see note on page 2