User manual

Chapter 4 Configuration
Page 81 ©February 2009
Configuration software allows the Fieldbus Interface IN and OUT areas to be addressed as an
array of 8-bit bytes (Byte Address Mode) or an array of 16-bit words (Word Address Mode). The
address mode may be required to change depending on the transfer mode, the protocol, or the
particular host device. The Address Mode option is included so that the configuration software
can be setup to use the same I/O addressing method used by the host device. The actual structure
of I/O in this database can only be physically altered via the transfer mode.
The Fieldbus Interface IN and OUT areas are simply a block of I/O memory, exchanged
according to the configured protocol. For example, with a Profibus slave that supports 244 bytes
of inputs, the fieldbus interface IN area could be addressed either as byte locations 1 to 244 or as
word locations 1 to 122. Note that in either case, the underlying database structure is unchanged,
the difference is limited to the Fieldbus IN/OUT Area address that is displayed by configuration
software.
Certain protocols have an inherent or preferred byte or word structure – for example, Modbus is
a protocol that usually operates on 16-bit (word) registers. Consequently, configuration software
will default to the most common address mode for that protocol. Configuration software may
also apply an offset and/or scaling to the IN/OUT Area addressing to suit the particular protocol.
For example ModbusTCP areas start from location 1, but other fieldbuses may start at location 0.
Note:
• The Fieldbus Interface IN and OUT Area both number from 0 - that is, there is an input 0 as
well as an output 0 (an offset may apply for some protocols).
• All IN/OUT Area locations accessed by the fieldbus must be part of a fieldbus mapping in
the 105G - that is, if a host device is writing to bytes 0 – 100 in the OUT Area, there must
be at least one fieldbus read mapping that uses these locations - if not, the Fieldbus Interface
will generate an error response message.
• Fieldbus mappings to/from the IN/OUT areas should always start at location 0 if possible (or
the lowest available unused location). Configuration Software will always automatically
choose the next lowest available location – it is strongly recommended that this topology be
used so as not to place unnecessary processing overhead on the module.
4.9.5 Fieldbus Mapping Configuration
The example below shows the Fieldbus Mapping configuration screen when adding new or
editing existing Fieldbus Mappings. Starting from the left of the screen, the I/O Register
selection specifies the starting I/O Register from the Radio Interface (press the “…” button to
make a selection graphically). The I/O Count parameter specifies how many consecutive I/O
Registers are to be transferred or linked. Command Type and Transfer Mode specify the type of
Fieldbus Mapping (see Fieldbus Mappings table above). Finally, I/O Location specifies the IN or
OUT Area location in the Fieldbus Interface (see earlier diagram).