User manual

Chapter 4 Configuration
MAN_905G_1.16 Page 126
range is 40001 – 41024 of which the first 32 words (i.e. 40001 – 40032) are global output
data. However all output registers, including the global output registers, may also be read
from the module using the point-to-point command Read Holding Registers (0x03). The
possible input registers (Data From Network) range is 41025 – 42048 of which the first 32
words (i.e. 41025 – 41056) is global input data (i.e. data extracted from another network
device’s global output data). Only data not assigned to global input data (i.e. 41057 – 42048)
may be written by the point-to-point preset register commands.
4.13.4 Configuration
The “Node Address” will be the Modbus Plus network address of the 905G, (allowable
values are 1 – 64) and must be unique for the network segment. The “Source Address” will
be the Modbus Plus network address of another module on the network from which the 905G
will extract Global Data (i.e. Data From Network). “GDB I/P Count” (up to 32 words max)
specifies the amount of Global Data to extract from the “Source Address” each cycle. An
offset into the source unit’s global data (“GDB I/P Offset”) may also be specified in order to
read a specific portion of the 32 word global data of the source address. However, since only
32 words max of global data are produced, the sum of GDB I/P Offset and GDB I/P Count
must never exceed 32. After setting these parameters, the 905G I/O Registers must be linked
to Modbus Plus 40000 registers with appropriate “Fieldbus mappings”.
In the below example there is one “Fieldbus Write Mapping” (this will make available Data
To Network) and one “Fieldbus Read Mapping” (this will make available Data From
Network). When adding mappings, software will automatically adjust the available 40000
register address range depending on the command type (i.e. read or write fieldbus mapping),
see below.
The I/O Register selection below for the fieldbus read mapping illustrates the allowable
40000 register address range base upon the chosen command type.
The fieldbus write mapping links the 48 I/O registers 0 – 47 to the fieldbus interface 4X
registers 40001 – 40048. As described earlier, fieldbus interface registers 40001 – 40032 are
always assigned as Global Data Out registers (i.e. Data To Network), these registers will be
broadcast to the network on each token rotation cycle. The remaining registers (40033 –
40048) can be accessed via Modbus 40000 point-to-point Read Register commands described
in section 4.10.4. NOTE - the option also exists for the Global Data output registers 40001 –
40032 to be read by the point-to-point commands also.
The fieldbus read mapping links the 48 fieldbus interface registers 41025 – 41072 to the I/O
registers 50 – 97. As described earlier, fieldbus interface registers 41025 – 41056 are always
assigned as Global Data In registers (i.e. Data From Network). These registers will be filled
with Global Data broadcast by the “Source Unit” according to the “GDB I/P Offset” and
“GDB I/P Count” parameters. In the above example, the values of the Offset = 0 and Count =
32, indicating that the entire 32 word Global Data broadcast from the Source Unit will be
read into fieldbus interface registers 41025 – 41056. Other nodes on the network can write to
the remaining registers (41057 – 41072) only by using the Modbus point-to-point Write
Register commands described in section 4.10.3. NOTE – the point-to-point Write Register
commands can not be used to write to the Global Data Input registers 41025 – 41056.