iSMA-B-AAC20/Sedona Modbus
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Modbus data addresses
A Modbus device is not required to contain all four groups of data. For example, a metering
device may contain only holding registers. However, for each data group implemented, an
“address convention” is used.
The requests for data (made to a device) must specify a data
address (and range) of interest.
Modbus data in a device is addressed as follows:
Coils
—
Addressed at 00000
—
0nnnn decimal, or “0x” addresses
,
Inputs
—
Addressed at 10000
—
1nnnn decimal, or “1x” addresses
,
Input Registers
—
Addressed at 30000
—
3nnnn decimal, or “3x” addresses
,
Holding Registers
—
Addressed at 40000
—
4nnnn decimal, or “4x” addresses.
Note: the data addressing (at least in decimal and hex formats) is
zero-based
, where the first
instance of a data item, for example coil 1, is addressed as item number 0. As another
example, holding register 108 is addressed as 107 decimal or 006B hex.