Project 06/2005
Danaher
Motion
3.12.1. Communication
Phases
In SERCOS, one master controller and many drives are connected with the
fiber optic cable to form a communication ring.
The master attempts to establish communication in a step-by-step process.
This process is referred to as bringing up the ring. Each step is defined in
SERCOS as a phase. In order to bring up the ring, the system must proceed
successfully through five phases (0 through 4). The MC simplifies this
process by allowing you to specify at which phase you want the ring. In most
cases, you simply need to set the SERCOS property phase to 4. The main
exception to this is when configuring telegram Type 7 to include external
encoder data, which requires that you first set the phase to 2 and then to 4.
In phase 0, the master establishes synchronization by passing the
M
aster
S
ynchronization
T
elegram (MST) to the first drive. That drive passes it to the
next and so on until it is returned to the master, indicating that the ring is
complete. After the master determines that 10 MST telegrams have been
passed through the ring, phase 0 is complete.
In
phase 1
, the master sends the
M
aster
D
ata
T
elegram (MDT). Each
drive is addressed individually and each drive responds with an
A
mplifier
T
elegram (AT). When all drives have responded, phase 1 is
complete.
In
phase 2
, all drives are configured through a series of IDNs. First, the
communication parameters are sent. Then, the drives are configured for
operation.
Up to this point, all data have been sent via the service channel. In
phase 3
, the cyclic data channel is established. Configuration is
completed and verified.
Phase 4
is normal SERCOS operation.
SERCOS.PHASE automatically moves the SERCOS ring through each
phase. You can observe this operation by watching the 7-Segment LED
display on the SERVO
STAR
drive. The number displayed indicates the
current communication phase. When the process is complete, an S (or 5) is
displayed, indicating that the ring is up and drives can be operated.
3.12.2. Telegrams
All SERCOS data are organized into data packets called telegrams.
Telegrams transport data and also provide protocol support and error
checking. SERCOS provides three telegrams, which are issued in order:
M
aster
S
ynchronization
T
elegram (MST)
A
mplifier
T
elegram (AT)
M
aster
D
ata
T
elegram (MDT)
76 Rev
E
M-SS-005-03l