14.3.2 CIM/CIU 500 Modbus TCP communication faults
Fault Possible cause Remedy
The slave does not respond to telegrams. Configuration or wiring error.
• Check the visual diagnostics on the Modbus
slave. Normal conditions are that the Grundfos
GENIbus LED2 is permanently green and that
the Modbus TCP LED1 is off or flashing green. If
not, see section LED status.
• Make sure that the cable between the Modbus
TCP master and the Modbus slave is connected
correctly.
• Ensure that the slave IP address is configured
correctly, and that the correct slave IP address is
used in the Modbus master poll.
The slave responds with exception response 0x01
"Invalid function".
The master is trying to use an unsupported function
in CIM/CIU 500.
Modbus function code overview for supported
function codes. Note that reading and writing coils
are not supported, so only register functions and
diagnostics are valid.
The slave responds with exception response 0x02
"Invalid data address".
The master is trying to read or write an invalid data
address. If a master tries to read register addresses
that are not listed in the tables, the slave responds
with this exception response. Some masters may
automatically try to read large blocks in one
telegram, which will cause problems if some of the
registers in the block are not supported. An example
would be reading the CIM configuration and CIM
status blocks in one telegram. This is not possible
since there are unused addresses among the
blocks.
Avoid reading or writing invalid data addresses.
Ensure that a block of registers starting at address X
is addressed as X - 1 in Modbus telegrams,
according to the Modbus standard.
The register address offset may have been changed
from default.
Read the holding register at address 00002
"Register Offset" to see if this value is different from
0. If so, write the value 0 to this address to make the
slave return to the default used in this functional
profile.
The slave returns data value 0xFFFF (65535).
The value is unavailable. A data value of 0xFFFF
does not necessarily indicate an error condition. It
means that the value is unavailable from the E-
pump.
See section Modbus register addresses for available
data.
The E-pump is not configured to show the value or
lacks a sensor to read the value.
See section Pump data register block for data values
that require a sensor.
The slave does not react to control actions or to
writing of settings.
The E-pump might be in "Local" mode, in which
case Operating mode, Control mode and Setpoint
cannot be changed from bus. Register 00201 bit 8
AccessMode must be "1" (=Remote) for bus control
to be active.
Set the E-pump in "Remote mode" by setting
register 00101 bit 0 RemoteAccessReq to "1" (=
Remote). The E-pump should show "Controlled from
bus" when status is read in Grundfos GO.
Related information
7.1 Connecting the Ethernet cable
7.3 Setting the IP addresses
8. Modbus function code overview
9.7 Pump data register block
14.3.1 LED status
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