Siemens SIMATIC S5 Manual page 289

Reaction times in the ET 200 distributed I/O system
Power-up phase/
steady-state
operation
Contribution of the
station connecting
cycle to t
R
Data cycle
Conditions for
diagnostics cycle
What is a token?
C-22
As regards the exchange of data between DP master and DP slave, a
distinction is drawn between the power-up phase and steady-state
operation.
Power-up phase: The DP master runs the program shown in Fig. C-10
once, starting with the station connecting cycle. This is followed by
steady-state operation.
Steady-state operation: The DP master runs the program repeatedly, the
only change being the station connecting cycle. The station connecting
cycle is repeated only in the event of an error.
The individual program parts are described below, along with the effects they
have on the reaction time t
Table C-15 lists the events which cause the DP master to run the station
connecting cycle. The table also shows how this response affects the reaction
time.
Table C-15 Reaction times in the station connecting cycle
Event
The DP master The DP master checks whether all DP slaves configured with
runs up COM ET 200 are addressable (= power-up phase).
(power-up
In the subsequent data cycle, the DP master takes into account only
phase)
those DP slaves which it identified as addressable.
The DP master If a DP slave is not accessible or could not be addressed in the
is in steady-state power-up phase, the DP master runs the station connecting cycle
operation. for the non-addressable DP slave.
In the data cycle the DP master sends output data to the DP slaves and
receives their input data.
Only those DP slaves which were identified as addressable in the station
connecting cycle are taken into account in the data cycle.
The reaction time t corresponds to the actual reaction time (see Section C.5)
R
when only the data cycle is run (in error-free operation).
A diagnostics cycle takes place only if the diagnostic report of at least one
DP slave has changed.
If there is more than one DP master on the SINEC L2 DP bus (i.e. two or
more DP masters), at any given time only one DP master can have
permission to access the bus.
Access permission (the token) is passed to each DP master in turn. In the
periods in which it does not have the token, a DP master cannot address its
DP slaves.
.
R
Response of IM 308-C in
station connecting cycle
ET 200 Distributed I/O System
EWA 4NEB 780 6000-02a