Echelon i.LON SmartServer 2.0 - Manual (Page 265)

i.LON SmartServer 2.0 Programmer’s Reference 15-16
Property Description
• DO_WORD_SWAP. Data is first arranged from highest to
lowest order, but every pair of 16-bit words is swapped.
For example, consider a device that uses an unsigned 32-bit
integer to report runtime accumulation. Selecting the data
ordering scheme is required because the Modbus protocol leaves
the interpretation of 32-bit integers to the discretion of the
implementer.
In Big Endian format, the value of 120,000 hours (0x01D4C0 in
hexadecimal format) would be represented as a value of: 00 01
D4 C0 in memory. This requires two adjacent Modbus registers
(each holding 16 bits of data). If the device manufacture defines
the unit runtime to be at register address 0x8, the Big Endian
formatted response to a read function would return data 0x0001
0xD4C0 in that order.
Now suppose the manufacture states the U32 value is returned
in Little Endian format. One interpretation of the value returned
to the driver from the read function would be 0xC0D4 0x0100.
Alternatively, the manufacture may interpret Little Endian to be
the ordering of registers and not bytes. In this case, the read
function would return 0xD4C0 0x0001 and the driver would
need to swap words to handle the value. If the device returned a
value of 0x0100 0xC0D4A, a byte swapped format would need
to be applied.
The frequency in which the SmartServer’s internal data server
polls the Modbus data point. The recommended minimum poll
rate is 30 seconds; the maximum poll rate is 1 second.
The default poll rate for Modbus data points is 20 seconds.
Note: The actual poll rate is determined by calculating the least
common denominator of all the poll rates set for the data point
from the applications to which it has been added.
15.4.3 Using the Set Function on Modbus Data Points
You can use the Set function to overwrite the configuration of a Modbus data point, or to create a new
Modbus data point. The input parameters you supply to the function will include one or more
elements. Each element includes a property that specifies a unique Modbus
data point to be created or modified.
Each element may also include a series of properties that define the configuration of the new
(or modified) Modbus data point. This set of properties is the same whether you are creating a new
Modbus data point or modifying an existing Modbus data point.
• If you are creating a new Modbus data point, you need to specify the ,
, and properties; all other properties are optional.
• If you are modifying an existing Modbus data point, you must specify the
property. In addition, all other properties should be filled; otherwise the values stored in them are
erased. The previous section, Using the Get Function on Modbus Data Points, details the
properties you can include in the Set function.