Dat
e of
I
s
sue
04/
22/
2008
Par
t No.
194341
Optical data coupler LS611
Special notes on the use of several masters
20
7.2
Notes on the adjustment of the PROFIBUS operating parameters
Optical data couplers are to be considered a cable extensions.
For this reason, no changes have to be made to the PROFIBUS parameters, if all stations
connected to the bus correspond to the PROFIBUS DP standard.
PROFIBUS FMS devices are not subject to the performance characteristics (such as re-
sponse time) of the PROFIBUS DP standard.
The time parameters here may be observed as follows:
An optical data coupler LS611 delays the signal by 15 bit times and 1 µs (table 7.3, “Time
parameter of the optical data coupler LS611,” on page 20).
In case of PROFIBUS stations which are known to be slow (such as software based test
computers), the slot time "TSLOT" should be increase by the value of the delta slot.
Table 7.3
Time parameter of the optical data coupler LS611
8
Special notes on the use of several masters
When using the PROFIBUS protocol, the time sequence of the bus traffic is determined
by the "active" bus station or by a master. In general, the PROFIBUS DP has been de-
signed as a mono master system, which means that there is only one master in the bus
segment, which as a rule is used as an interface to the control system (or PLC). This
master is referred to as Class1-Master. All other stations are passive, and are referred to
as slaves.
In some applications, however, several active stations are used, which frequently may
be the case in operating elements ("touch panels"), for example. However, due to their
communication relationship to the PLC these devices also have to have the properties of
an active station. As no fast (cyclical) connections are operated with slaves, and the
Class1-Master only is used for communication as a rule, it is not always realized that
such a station also has the functional range of a master. In this case, a so-called "Class2-
Master" (acyclical connection) is used.
The existence of the Class2-Master within a certain topology is significant for the analysis
of sequence errors after the interruption of the light beam.
If two optical data couplers wired after each other (for the additional transmission in Y
direction, for example), (cf. illustration 8.1), and if the Class2-Master is located behind the
During the setting mode, no changes are carried out. The device contin-
ues to operate with the previous baud rate without interruption. As the
C1CP function has an effect only when the light beam is interrupted,
switching on or off has not influence on the normal operation.
Baud rate
Absolute delay
DeltaSlot
[kBit/s]
[bit]
[µs]
[bit]
1,500
17
11.1
34
500
16
31
32
187.5
15
80.8
31
93.75
15
161
31
