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5.10.3 Register Remap Configuration
At times, it may be convenient to access inverter registers in bulk Modbus transactions. This may be
especially true in situations where it is desired to access certain registers that are natively non-
contiguous. For example, if it were desired to read the inverter’s operating frequency (register 2058),
DC link bus voltage (register 2070), and operation status (register 2063), 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 2058 for a quantity of 13
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 (5001..5050) 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 56 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.
Figure 56: Modbus/TCP Register Remap Configuration
As an example, the configuration shown in Figure 56 reveals that a total of five inverter registers have
been remapped: register 1798 (frequency command) has been remapped to register 5001, register 1799
(operation command word) has been remapped to register 5002, register 2058 (output frequency) has
been remapped to register 5003, register 2070 (DC link bus voltage) has been remapped to register
5004, and register 2063 (operation status word) has been remapped to register 5005. With this
configuration, it is now possible to efficiently interact with these five non-contiguous inverter registers via
just two Modbus “read/write multiple registers” transactions. Writing to the frequency command and
command word can be accomplished with a single “write multiple registers” transaction by writing a
quantity of two registers starting at register 5001. Similarly, reading the output frequency, DC link bus
voltage and operation status word (in that order) can be accomplished with a single “read multiple
registers” transaction by reading a quantity of three registers starting at register 5003.
