20
8.2 Modbus GSM/GPRS communication faults
Fault
Possible cause
Remedy
1. The slave does not respond to
telegrams.
a) Configuration or installation error.
• Ensure that the CIU 250 has contact with
the GSM network. The LED1 should be
pulsing yellow.
If the LED1 signal is incorrect, see
section
for
correct installation of the CIM 250.
• Ensure that the correct slave address is
used in the Modbus master poll.
See register 00003 ModbusAddress
(factory value is 00231).
b) The slave may be in listen-only mode.
• Either send a restart communications
diagnostics command, or restart the
MP 204 manually.
c) If the holding register of address 00001
"SlaveMinimumReplyDelay" is set too
high, the master may time out before
receiving the response from the slave.
• Increase the reply delay in the master or
reduce the "SlaveMinimumReplyDelay"
in order to communicate.
2. The slave responds with exception
response 0x01: "Invalid function".
a) The master is trying to use an
unsupported function in the CIU 250.
• See section
for supported function codes.
Note that reading and writing coils are not
supported, so only register functions and
diagnostics will be valid.
3. The slave responds with exception
response 0x02: "Invalid data address".
a) 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 will respond 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 register blocks in one
telegram: this is not possible since there
are unused addresses among the blocks.
• Avoid reading or writing invalid data
addresses.
4. The slave returns data value 0xFFFF
(65535).
a) The availability of data will in some cases
depend on a configuration or the actual
conditions of the system (e.g. trying to
request data from a pump which is not
present will return "data not available"
(0xFFFF)).
• See section
for available data.
b) With its present configuration or operating
mode the MP 204 is unable to supply the
requested data.
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5. The slave does not react to control
actions or to writing of settings.
a) The CIU 250 is SCADA PIN-code-
protected (GeneralStatus register 00029,
bit 0 = 1), and an incorrect PIN code has
been written.
Write access requires a correct PIN code
(ScadaPinCode, register 00011). Writing
the correct PIN code value will trigger the
write access control, and write access will
be open, which can be verified with
GeneralStatus, register 00029, bit 1 = 1.
