Siemens SINUMERIK 840D sl Function Manual page 889

The online interface is available for each of the two online control units separately.
After a successful online request sequence, the control unit receives the number of its online
interface from the PLC.
The HMI parameters are then transferred to the corresponding online interface by the PLC.
The control unit goes online and occupies its own online interface via which data are then
exchanged between the HMI and PLC.
HMI data interfaces
User data from/to the HMI are defined on these:
● DBB 0-49 control unit 1 interface
● DBB 50-99 control unit 2 interface
These data and signals are always needed to operate control units.
M:N sign-of-life monitoring
This is an additional monitoring function which must not be confused with the HMI sign-of-life
monitor. For further information, please refer to the relevant signals.
In certain operating states, control units with activated M:N switchover (parameterizable in
NETNAMES.INI) must be capable of determining from a PLC data whether they need to wait
or not before linking up with an NCU.
Example:
Control units with an activated control unit switchover function must be capable of starting up
an NCU without issuing an online request first.
Control unit must go online for service-related reasons.
The operation is coordinated in the online request interface via data DBW110: M_TO_N_ALIVE
The M:N sign of life is a ring counter which is incremented cyclically by the PLC or set to a
value of 1 when it overflows.
Before a control unit issues an online request, it must check the sign of life to establish whether
the M:N switchover is activated in the PLC.
Procedure:
HMI reads the sign of life at instants T0 and T0 + 1.
Case 1: negative acknowledgement for reading process, DB19 does not exist. Control unit
goes online without request procedure.
Case 2: m_to_n_alive = 0, control unit switchover disabled. Control unit goes online without
request procedure.
Case 3: m_to_n_alive (T0) = m_to_n_alive (T0+1), control unit switchover disabled. Control
unit goes online without request procedure.
Case 4: m_to_n_alive (T0) <> m_to_n_alive (T0+1), control unit switchover enabled.
Case 1 ... case 3 apply only under special conditions and not in normal operation.
Extended Functions
Function Manual, 10/2015, 6FC5397-1BP40-5BA3
Z2: NC/PLC interface signals
19.2 Distributed systems (B3)
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