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Data transfer
ServoOne User Manual SERCOS II and III
ID no.: 1108.26B.3-00 Date: 04/2020
Data transfer
7 Data transfer
7.1 Communication phases
The establishment of communication between the master and slaves via SERCOS
is divided into six communication phases. As long as the slave has not received a
SERCOS telegram, it is in the "NRT (Non-RealTime)" phase. Communication phases
0 and 1 are used to detect the bus users. The timing and data for the protocols
for communication phases 3 and 4 are prepared and the drive configured in
communication phase 2.
On the transition to communication phase 3 the drive parameter settings, as far as they
relate to the SERCOS profile, are checked for plausibility. If there is an error, switching
to communication phase 3 is denied with a corresponding error. The phases are
started in ascending order. It is only possible to go back a phase via communication
phase 0. The communication phase is specified by the master. The initialisation is
completed with the switch to communication phase 4 and it is possible to switch on the
power circuit.
The actual communication phase is indicated with the aid of the parameter 22000
"COM_SERIII_ScopeVars", index 1.
7.2 SERCOS II - cyclic data transmission
To synchronise the drives in the ring, the master synchronisation telegram (MST) is sent
at the start of each SERCOS cycle (cycle time t
S
cyc
= S-0-0002) (see figure below). This
only information this telegram contains is the communication phase specified by the
master. The content of the master data telegram (MDT) and drive telegram (AT) can be
configured. A common master data telegram for all drives is sent to the drives by the
controller once per SERCOS cycle. This telegram contains the master control word,
the service channel (parameter channel) and a configurable data block. This data block
mostly contains reference values and limits that the controller wants to send to the drive
for the operation of the related operation mode. The content of this data block can be
configured using the telegram setting.
The master data telegram is received by all the drives in the ring at the same time.
A separate drive telegram is also sent to the controller by each drive once per SERCOS
cycle. This telegram contains the drive status word, sections of the service channel and
a configurable data block. This data block mostly contains actual values and status
values that the controller needs for the operation of the related operation mode.
Figure 7.1
AT
AT
AT
MDT
t
m
2 1
1.1
t
1.2
t
1.M
t
2
t
Scyc
AT
M
t
1.m
AT
AT
AT
MDT
t
m
2
1.1
t
1.2
t
1.M
t
2
t
Scyc
AT
M
t
1.m
MST
MST
Timing diagram, SERCOS cycle
7.3 SERCOS III - cyclic data transmission
The cyclic data transmission starts in communication phase 3. With the aid of the
cyclic data transmission, parameters are transmitted with each cycle of the bus. The
cycle time is configured with the aid of the IDN S-0-1002.0.0. Which parameters are
transmitted cyclically is defined with the aid of the mapping.
7.3.1 Mapping the configurable real-time data
The real-time data are mapped as a rule in the master (that is the higher level controller).
With the aid of parameters S-0-1050.0.6 and S-0-1050.1.6 you can check which
parameters are mapped to the MDT and the AT.
In principle not all parameters can be transmitted as real-time data. The parameters
that can be transmitted in the MDT are entered in the IDN S-0-0188.0.0. All parameters
that can be transmitted in the AT are listed in the IDN S-0-0187.0.0.
In the situation that manufacturer-specific parameters that are field parameters are to
be mapped, the first index is always mapped automatically.