Siemens SIMATIC S7-300 FM 350-1, Руководство пользователя

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Operating Modes, parameters and commands
7.2 Isynchronous mode
FM 350-1 Counter module
Manual, 05/2011, A5E03648639-01
85
7.2 Isynchronous mode
Note
Basic information on isochronous mode is available in the SIMATIC Isochronous Mode
(
Hardware requirements
Requirements of operating FM 350-1 in isochronous mode:
●
The CPU supports isochronous mode
● The DP master supports constant bus cycle times
Principle of isochronous operation of FM 350-1
FM 350-1 supports non-isochronous and isochronous mode, depending on the configuration.
The default is non-isochronous mode. FM 350-1 automatically changes to isochronous mode
if configured accordingly, without signaling the change.
In isochronous mode, data are exchanged between the DP master and FM 350-1 in
synchronism with the PROFIBUS DP cycle, i.e.:
●
All control signals transferred to FM 350-1 are activated at the time T
o
within the same
PROFIBUS DP cycle.
● All values and FM 350-1 status bits recorded at the time T
i
are made available at the
checkback interface within the same PROFIBUS DP cycle.
All 16 bytes of the checkback interface are consistent when operating in isochronous
mode, i.e., the values and status bits always match.
● The counter value which is influenced by signals at the digital outputs can only take effect
within the same PROFIBUS DP cycle if the event occurred prior to time T
i
of this
PROFIBUS DP cycle. This applies to the following actions:
–
Load counter by opening the hardware gate
– Load counter by synchronization
– Latch and latch / retrigger a counter value
Parameter errors will prevent FM 350-1 from changing over to isochronous mode.
If isochronous mode is blocked as a result of errors or failure / delay of Global Control (GC),
FM 350-1 will ignore the error and returns to isochronous mode at the next cycle.
The checkback interface will not be updated if isochronous mode is deactivated.