Siemens SINUMERIK 840D sl Commissioning Manual page 365

Error
HMI displays alarm 120202 "Wait for connection to NC/PLC" and/or no values (only '#').
SINUMERIK Operate (IM9)
Commissioning Manual, 03/2013, 6FC5397-1DP40-3BA1
Possible error causes and remedies
The NCU has a valid IP address in the system network, however, not the required IP
address.
The NCU participates in DHCP operation and was not able to obtain the corresponding
required IP with the target address saved in the MMC.INI; this is the reason that it was
dynamically allocated an address. A reason for this could be that the required IP was
configured twice in the system network, or the required IP is not in the reserved range, but
is located in the dynamic address range. This is a configuration error.
Remedy 4.3
The same as for remedy 4.1
Error cause 4.4
The NCU has a valid IP address in the system network, however, not the required IP
address.
The NCU participates in DHCP operation as DHCP client and has a required IP that has
been set but which does not match the system network. For instance, this situation occurs if
a network address was used in the system network other than the default network address,
but it was forgotten to change over the required IP of the NCU to this address range. The
NCU is allocated an IP address that matches the system network from the dynamically
allocated range, but which is different from its 'old' required IP that was not changed over.
Up to and including SW 2.4.1, in this situation, the NCU cannot be addressed in the system
network. The reason for this is that it has internally established its firewall regarding the
required IP that was entered for it, which does not match the system network - which is why
it does not respond at X120.
Remedy 4.4
The same as for remedy 4.1
Error cause 5.1
There is no physical connection.
Possible error causes include:
A switch is not closed/has failed; this can also be the switch of an MCP
•
The cable connection has become loose (poor contact)
•
An incorrect cable was used (crossover/not crossover)
•
A cable being used as data link is defective
•
Remedy 5.1
Establish a physical connection.
Service and diagnostics
18.11 Station-related network diagnostics
359