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MSD Servo Drive User Manual SERCOS II
15
[ Chapter 3 ]
3 SERCOS communication
phases
Communication over the SERCOS bus between the master and slaves is divided into
five phases. Communication phases 0 and 1 identify the stations on the bus. In com-
munication phase 2 the time and data structure of the protocols for phases 3 and 4 are
prepared and the drive is configured. At the transition to communication phase 3 the
drive parameter settings relating to the SERCOS profile are checked for plausibility. In the
event of a fault, the switch to communication phase 3 is refused with a relevant fault
message. The phases are run through in ascending order. It is only possible to drop back
a phase by way of communication phase 0. The communication phase is dictated by
the master. On switching to communication phase 4, the initialization is completed and
power-up is enabled.If the phase sequence is interrupted, the status indicator remains
stuck at the last communication phase reached. The current communication phase is
indicated by way of a flash code by LED H5. Intervals of about one second unlit are
followed by LED H5 flashing briefly “n” times, “n” being the number of the current com-
munication phase.
3.1 Communication phase 0
When communication phase 0 is active, automatic baud rate detection in the drive has
completed successfully. The drive is in communication phase 0 and is waiting for the
master to switch from phase “0” to “1”. During communication phase 0 the green LED
H5 on the drive unit remains unlit.
LED H5 flash code Status
▂▂▂▂▂▂▂▂▂
H5H4
Indication of communication phase 0
Table 3.1 Flash code: Communication phase 0
3.2 Communication phase 1
If communication phase 1 is active, the drive is in phase 1. The master has not yet trig-
gered a switch from phase “1” to “2”. During communication phase 1 the green LED H5
on the drive unit cyclically displays the flash code set out in the following table.
LED H5 flash code Status
█▂▂▂█▂▂▂
H5H4
Indication of communication phase 1
Table 3.2 Flash code: Communication phase 1
3.3 Communication phase 2
Communication phase 2 signifies that the drive is in parameter-setting mode. IIn this
mode you can write to many parameters which are no longer editable in communica-
tion phase 4 (operation mode). In communication phase 2 the communication param-
eters are usually transferred from the master to the drive. All parameters influencing
the switching frequency or the sampling times of the loop control system can likewise
be written only in communication phase 2. During communication phase 2 the green
LED H5 on the drive unit cyclically displays the flash code set out in the following table.
To enter communication phase 2, the master specifies “Communication phase 2” in the
Master Sync Telegram.
Before the system can switch to communication phase 3, command S-0-0127 - Prepare
switch to communication phase 3 - must be executed. During this preparatory phase the
drive checks criteria including the validity of the parameters required for communica-
tion phase 3. When the prepare-to-switch command has been successfully executed,
the drive is switched to communication phase 3 by the master. In the event of a fault
(plausibility of the setting concerned), the switch to communication phase 3 is refused
with a relevant fault message.
NOTE: On switching to phase 3, the servo drive performs all the necessary ini-
tializations. If it is not possible to switch to phase 3 because of faulty parameter
setting, the drive generates a relevant fault message. The meanings of the fault
numbers are listed in the MSD Servo Drive Application Manual.
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