Siemens SINUMERIK Series Function Manual page 850

Z2: NC/PLC interface signals
18.2 Distributed systems (B3)
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.
850
Function Manual, 03/2013, 6FC5397-1BP40-3BA1
Extended Functions