5.2.1 PROFIBUS DP-V1 Introduction
The PROFIBUS DP extension DP-V1 offers acyclical
communication in addition to the cyclical data communi-
cation 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).
Cyclical communication means that data transfer takes
place continuously with a certain refresh rate. This is the
known DP-V0 function normally used for quick update of
I/O process data.
Acyclical communication takes the form of a once-off data
transfer event, mainly 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
•
Cyclical data exchange (DP-V0)
•
Acyclical 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, etc. The master class 1
acyclical connection can be used for general parameter
access in the slaves. However, the acyclical connection is
fixed, and cannot be changed during operation.
5.2.3
Features of a Master Class 2
Connection
•
Initiate/abort acyclical connection
•
Acyclical read/write from and to parameters
The master class 2 acyclical connection is typically used for
configuration or commissioning tools for easy access to
each parameter in any slave in the system. The acyclical
connection can be dynamically established (initiate) or
removed (abort) even when a master class 1 is active on
the network.
5.2.4
Services Overview
Master
type
Service
Read Write Data
transport
Initiate Abort Alarm
read
data
from
follower
write
data to
follower
read and
write data
open a
connection
close a
connection
Master
Class 1
yes yes yes - - -
Master
Class 2
yes yes yes yes yes -
Table 5.1 Services Overview
5.2.5
Principle of Data Exchange by
PROFIBUS DP-V1
In a DP cycle, the master class 1 (MC1) first updates the
cyclical process data for all slaves in the system. The MC1
then sends one acyclical message to one slave. If a master
class 2 (MC2) is connected, the MC1 hands over the bus
rights to MC2, which is then permitted to send one
acyclical message to one slave. The token is then handed
back to the MC1, and a new DP cycle begins.
Illustration 5.1 DP Cycle
•
MC: Master class
•
C1...Cn: Cyclical data
•
AC1: Acyclical data master class 1
•
AC2: Acyclical data master class 2
PROFIBUS DP services are activated via specific service
access points (SAP). Table 5.2 shows the SAP specified for
acyclical communication.
Master
SAP
Follower SAP Meaning
50 (32H) 49 (31H) Master Class 2: Initiate request
50 (32H) 0..48 (0..30H) Master Class 2: Abort, read, write, data
transfer
51 (33H) 50, 51 (32H,
33H)
Master Class 2: Alarm
51 (33H) 51 (33H) Master Class 2: Read, write
Table 5.2 Service Access Points (SAP)
5.2.6
DP-V1 Features for Parameter Access
This section describes how to use DP-V1 for accessing VLT
parameters.
The standard PROFIBUS DP-V1 read and write services are
not sufficient for accessing the many parameters and
attributes in the frequency converter. For this reason, the
PROFIdrive parameter channel is defined. Using this
parameter read/write is performed by addressing a single
DP-V1 object in the frequency converter as shown in the
example, Table 5.3.
Parameter Access
Programming Guide
24 Danfoss A/S © Rev. 05/2014 All rights reserved. MG37G102
55
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