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were desired to read the inverter's status 1 word (register 1302), torque
(register 1319) and output voltage (register 1306), this could be accomplished
in two different ways:
1.
Implement three separate Modbus read transactions, each one
reading one register only, or
2.
Implement one single Modbus read transaction, starting at register
1302 for a quantity of 18 registers. Then, pick out the registers of
interest and ignore the rest of the response data.
While both of these methods will certainly work, neither one of them is
optimized for the task at hand, which is to access three specific register values.
A fully optimized solution can be realized, however, by making use of the
interface card's Modbus register remapping capabilities. This mechanism
operates by allocating a block of 50 user-configurable registers (2001..2050)
that remap to other inverter registers. In this way, non-contiguous inverter
registers can be grouped together in any order and accessed efficiently via the
Modbus TCP "read multiple registers" and "write multiple registers" function
codes. The net effect is one of being able to transfer larger blocks of registers
using fewer Modbus transactions, which results in improved network utilization
and simpler data manipulation code on the Modbus master device.
Figure 49: Modbus TCP Register Remap Configuration
Figure 49 shows the register remap configuration array. Clicking on an entry
field in the "Remaps To" column allows the user to enter an inverter register
number that will then be accessible at the register indicated in the adjacent
"Register" column. An assignment of 0 in the "Remaps To" column indicates
that no inverter register is remapped at that location, which results in written
values being ignored and read values returned as a default value of 0. Note
that remapped inverter registers are still accessible at their original locations:
remapping simply provides an additional means of accessing the original
register's value.
As an example, the configuration shown in Figure 49 reveals that a total of six
inverter registers have been remapped: register 1007 (command 1 word) has
50
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