Communication
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7.2 Modbus Register Address Aliasing
When addressing the Modbus interface, the positioning/grouping of the existing function registers
may make PLC programming difficult in some applications. Grouping of required monitoring, as well
as programming, registers may affect the efficiency of the PLC when it requires block fetching and
setting of data. With this in mind, the Synergy Plus Modbus address map has a section of user
programmable registers, through which up to 16 register aliases can be set. Alongside these there
are 16 four byte addresses that correspond with the aliases and act as the data conduits for each
select address.
Alias Register
Addresses
16 bit Alias Registers Data Address
32 bit values ( 2
Word )
17600
e.g. 32000 (base 10) 17664
0x12345678 (HEX)
17601
17666
17602
17668
..
…
..
…
..
…
17615
17696
The table shows the relationship between the Alias Registers and the Data Registers. The data can
take any data type that can fit into 4 bytes. So any address that yields 6 bytes data, such as time,
will be incomplete. The access of 1 and 2 byte datum will have redundant bytes in the frame used.
Below is an example of what will happen with different sizes.
Alias
Address
Addresses
Alias
Addresses
base10
Name
Data
addresses
Data Shown in 4 Bytes.
Greyed have no meaning
or affect.
17600
26880
Start I Limit
17664
0x00 0x00 0xe8 0x6c
17601
26944
Start I Time
17666
0x00 0x00
0x01 0x0e
17602
704
Start
Pedestal
17668
0x00 0x00
0x0c 0xcd
17603
21120
iERS
enabled
17670
0x00 0x00 0x00
0x00
17604
21184
iERS rate
17672
0x00 0x00
0x00 0x00
17605
21320
Start Saving
Level
17674
0x00 0x00 0x00 0x00
Using the above example, the gathered values may be seen in the following diagram. In this
instance block setting of the 6 remapped registers is shown.
