MG.90.A2.02 – VLT is a registered Danfoss trademark
20
FCM 300 PROFIBUS / VLT 2800 PROFIBUS
DP
Example of SPM execution
In the VLT the SPMs are temporarily stored in a FIFO
buffer. This means that up to 16 consecutive SPMs
can be retained. If only one SPM has entered the
FIFO, the VLT will resume normal communication as
soon as the SPM has been acknowledged by the
master (and the condition causing the SPM been
rectified). If more SPMs are in the FIFO, these will be
transmitted consecutively upon acknowledgement. If
more SPMs are triggered when the FIFO is full, these
will be ignored.
■
Synchronize and freeze
The control commands SYNC/UNSYNC and
FREEZE/UNFREEZE are broadcast functions. SYNC/
UNSYNC is used to send syncronized control
commands and/or speed reference to all the
connected slaves (FC motor Series/VLT 2800 Series).
FREEZE/UNFREEZE is used to freeze the status
feedback in the slaves to get syncronized feedback
from all connected slaves.
The synchronize and freeze commands only affect
Process Data (the PCD part of the PPO).
SYNC/UNSYNC
SYNC/UNSYNC can be used to obtain simultaneous
reactions in several slaves, for example synchronised
start, stop or speed change. A SYNC command will
freeze the actual control word and speed reference,
incoming Process Data will be stored but not used
until a new SYNC command or a UNSYNC command
is received.
See the example below where the left column holds
the speed reference send out by the master and the
three right columns hold the actual speed reference
used in each of the three slaves.
Actual slave speed reference
VLT
VLT
VLT
From DP master to address:
Address 3
Address 4
Address 5
1. Speed reference = 50 % to address 3
⇒
50 %
0 %
0 %
2. Speed reference = 50 % to address 4
50 %
⇒
50 %
0 %
3. Speed reference = 50 % to address 5
50 %
50 %
⇒
50 %
4. SYNC command to all addresses
⇒
50 %
⇒
50 %
⇒
50 %
5. Speed reference = 75 % to address 3
⇒
50 %
50 %
50 %
6. Speed reference = 75 % to address 4
50 %
⇒
50 %
50 %
7. Speed reference = 75 % to address 5
50 %
50 %
⇒
50 %
8. SYNC command to all addresses
⇒
75 %
⇒
75 %
⇒
75 %
9. Speed reference = 100 % to address 3
⇒
75 %
75 %
75 %
10. Speed reference = 50 % to address 4
75 %
⇒
75 %
75 %
11. Speed reference = 25 % to address 5
75 %
75 %
⇒
75 %
12. UNSYNC command to all addresses
⇒
100 %
⇒
50 %
⇒
25 %
13. Speed reference = 0 % to address 3
⇒
0 %
50 %
25 %
14. Speed reference = 0 % to address 4
0 %
⇒
0 %
25 %
15. Speed reference = 0 % to address 5
0 %
0 %
⇒
0 %
MASTER
SPM 2 NOT ACK.
REQ 1
REQ 2
SPM 1 ACK.
REQ 2
SPM 2 ACK.
SLAVE
RES. 1
SPM 1
SPM 2
SPM 2
RES. 2
0
0
0
0
0
0
0
1
1
1
PCA
SPM BIT
