Siemens SIMATIC S7-400H Manual page 55

Note
Process interrupts and diagnostic interrupts are stored by the I/O. If such
interrupts were set by modules of the remote input/output station they will be
caught up when the block is lifted. If they were set by modules of the central I/O
they can then only all be caught up if the particular interrupt request did not occur
again during the block.
If the PG/ES requested a master/standby switch-over then on conclusion of the
update the previous standby CPU becomes the master and the previous master
CPU switches to STOP mode. Otherwise the two CPUs go to RUN (Redundant
mode) and execute the user program in synchronism.
If a master/standby switch-over has been performed then in the next cycle after
the update OB 1 has its own identifier (see Reference Manual System Software for
S7-300/400, System and Standard Functions ). For other peculiarities when the
configuration is changed see section 5.2.3.
Delayed notification functions
The SFCs, SFBs and operating system services listed trigger messages to all the
parameters logged on in each case. These functions are delayed after the start of
the update.
SFC 17 "INTERRUPT_SQ", SFC 18 "INTERRUPT_S"
SFC 52 "WR_USMSG"
SFB 33 "INTERRUPT", SFB 34 "INTERRUPT_8", SFB 35 "INTERRUPT_8P",
SFB 36 "NOTIFY", SFB 37 "AR_SEND"
Symbol-related messages
Statuses
System diagnostics messages
From this time on instructions to block and release events via the SFC 9 "EN_MSG"
and the SFC 10 "DIS_MSG" will be rejected with a negative return value.
Communication functions with derived jobs
If a CPU receives one of the jobs listed below it must in turn generate
communication jobs from this and send these to other modules. This could be,
for example, instructions to read or write parameter data records from/to modules
of the remote input/output station. These jobs will be rejected until the update is
complete.
Read/write data records via O & M functions
Read data records via SSL information
Block and release messages
S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04
Link-up and Update
5-11