Danfoss VLT PROFIBUS DP MCA 101 Programming Manual page 28

Parameter Access
5.2.1 PROFIBUS DP-V1 Introduction
The PROFIBUS DP extension DP-V1 offers acyclic communi-
cation in addition to the cyclic data communication of DP
V0. This feature is possible using a DP master class 1 (for
example, PLC), as well as a DP master class 2 (for example
PC Tool).
Cyclic communication means that data transfer takes place
continuously with a certain refresh rate. This function is the
known DP V0 function normally used for quick updates of
5 5
I/O process data.
Acyclic communication is a one-off data transfer event,
used for read/write from and to parameters from process
controllers, PC-based tools, or monitoring systems.
5.2.2 Features of a Master Class 1
Connection
•
Cyclic data exchange (DP-V0).
•
Acyclic read/write from and to parameters.
A master class 1 is used as the process controller (either
PLC or PC-based), responsible for commands, speed
reference, status of the application, and so on. The master
class 1 acyclic connection can be used for general
parameter access in the slaves. However, the acyclic
connection is fixed and cannot be changed during
operation.
5.2.3 Features of a Master Class 2
Connection
•
Initiate/abort acyclic connection.
•
Acyclic read/write from and to parameters.
The master class 2 acyclic connection is typically used for
configuration or commissioning tools for easy access to
each parameter in any slave in the system. The acyclic
connection can be dynamically established (initiated) or
removed (aborted) even when a master class 1 is active on
the network.
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VLT PROFIBUS DP MCA 101
5.2.4 Services Overview
Master
type
Master
class 1
Master
class 2
Table 5.1 Services Overview
5.2.5 Principle of Data Exchange by
In a DP cycle, the master class 1 (MC1) first updates the
cyclic process data for all slaves in the system. The MC1
then sends 1 acyclic message to 1 slave. If a master class 2
(MC2) is connected, the MC1 hands over the bus rights to
MC2. MC2 is then allowed to send 1 acyclic message to 1
slave. The token is then handed back to the MC1, and a
new DP cycle begins.
Illustration 5.1 DP Cycle
•
•
•
•
PROFIBUS DP services are activated via specific service
access points (SAP). Table 5.2 shows the SAP specified for
acyclic communication.
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Service
Read Write Data Initiate
trans-
port
Read Write Read Open a
data data to and connec-
from slave write tion
slave data
Yes Yes Yes
Yes Yes Yes Yes
PROFIBUS DP-V1
MC: Master class.
C1...Cn: Cyclic data.
AC1: Acyclic data master class 1.
AC2: Acyclic data master class 2.
Abort Alarm
Close a
connec-
tion
– – –
Yes –
MG37G202