Update Sequence - Siemens SIMATIC S7-400H System Manual

9.3.2

Update sequence

What happens during updating?
The execution of communication functions and OBs is restricted section by section during
updating. Likewise, all the dynamic data (content of the data blocks, timers, counters and
memory markers) are transferred to the standby CPU.
Update procedure:
1. Until the update is completed, all asynchronous SFCs which access the I/O modules
2. Message functions are delayed until the update is completed (see list below).
3. The execution of the OB 1 and of all OBs up to priority class 15 is delayed.
4. Transfer of all data block contents modified since link-up.
5. The following communication requests are acknowledged negatively:
6. The system returns a negative acknowledgment of initial calls of communication functions
7. The system disables the generation of new requests of all OBs of priority class > 15, so
8. It generates the start event for the cyclic interrupt OB with special handling if its priority
S7-400H
System Manual, 09/2007, A5E00267695-03
(SFCs 13, 51, 52, 53, 55 to 59) initiate a "negative" acknowledgment with the return
values W#16#80C3 (SFCs 13, 55 to 59) or W#16#8085 (SFC 51). When these values
are returned, the jobs should be repeated by the user program.
In the case of cyclic interrupts, the generation of new OB requests is disabled, so no new
cyclic interrupts are stored and as a result no new request errors occur.
The system waits until the update is completed, and then generates and processes a
maximum of one request per cyclic interrupt OB. The time stamp of delayed interrupts
can not be evaluated.
– Reading/writing data records using OCM functions
– Reading diagnostic information using STEP 7
– Disabling and enabling messages
– Logon and logoff for messages
– Acknowledgement of messages
which manipulate the contents in RAM. See also
System and Standard Functions
with delay, after the update is completed.
new interrupts are not saved and as a result do not generate any request errors.
Queued interrupts are not requested again and processed until the update is completed.
The time stamp of delayed interrupts can not be evaluated.
The system no longer executes the user program or updates the I/O.
class is > 15, and executes this OB as required.
Note
The cyclic interrupt OB with special handling is particularly important in situations where
you need to address certain modules or program elements within a specific time. This is
a typical scenario in fail-safe systems. For details, refer to the
Programmable Controllers
Modules
manuals.
System Software for S7-300/400,
. All remaining communication functions are executed
S7-300 Programmable Controllers, Fail-safe Signal
and
Link-up and update
9.3 Link-up and update
S7-400F and S7-400FH
101