wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

Profibus 32-11
Buscycle T DP
T DX
GC
clock
GC
clear/
opera.
DX(B) DX(B) … … DX(B) MAC1
MS1
GC = Global control (Clock; clear/operate = Status of the DPM1)
DX(B) = Data exchange (Broadcast) of the MS0 relation
MAC1 = One acyclic service of the MS1 relation
MAC2 = One acyclic service of the MS2 relation
TC = Token
ASP = Active break
PSP = Passive break
T DP = Profibus DP cycle time
T Dx = Time for the transmission of the cyclic data
T
C
MAC2
T
C
ASP PSP
MS2
FIGURE 32.5
Timing of an MS1/MS2 connection with isochronous cycle.
is executed parallel to cyclic data communication, but with lower priority. Figure 32.3 shows some
sample communication sequences. The master class 1 has the token and is able to send messages to
or retrieve them from slave 1, then slave 2, etc., in a fixed sequence until it reaches the last slave of the
current list (MS0 relation); it then passes on the token to the master class 2. This master can then use
the remaining available time of the programmed cycle to set up an acyclic connection to any slave to
exchange records (MS2 relation); at the end of the current cycle time, it returns the token to the DPM1.
Similarly, as well as the DPM2, the DPM1 can also execute acyclic data exchange with slaves (MS1
relation) (Figure 32.5).
32.6.1 Variables
The field-device is composed of modules located in slots. Every slot has now a set of variables addressed
with an index in the range of 0–255. With the acyclic read and write services, it is possible to read and
modify these parameters of the field-device. The format and meaning of these parameters is defined in
the device profile.
32.6.2 Device Model including Identification and Maintenance
For the uniform identification and maintenance procedures, every device and module of a Profibus system
must be identified. The set of Identification and Maintenance (I&M) variables inside every Profibus
DP field-device permits this functionality. These variables are read and also written with the acyclic data
exchange services.
32.6.3 alarm Handling
The alarm-handling function allows a field-device to signal-detected alarm conditions in a controlled
procedure to the DPM1 controller. The controller has to acknowledge the signaled alarms.
Possible alarm conditions are pulled or plugged modules, diagnostic information, changed parameters
in the field-device, or user defined changes of process values.
© 2011 by Taylor and Francis Group, LLC