Data Structure; Modbus Data Formats And Byte Ordering - Siemens SENTRON 3WL10 Manual

Data structure

Units of information such as status information or measured variables are made available in
suitable data formats by products in the SENTRON range.
5.1

Modbus data formats and byte ordering

Identifying data points
Abbreviation
U8
U16
U32
U32SWAPPED
S32SWAPPED
FP32
FP64
TS
ST
Individual units of information are identified by register addresses. A register is 16 bits in
size. If a unit of information is larger than 16 bits, the unit of information will require the
corresponding number of registers.
The individual data types are stored as described in the table below:
Register
Register address
Register address
+1
Number of registers
Example of bit counting using a 32-bit data format:
Bit
Byte
Reg-
ister
System Manual, 04/2020, L1V30499596021-02
U8
High byte 0x00
Low byte Data byte
High byte –
Low byte –
1
31 – 24 23
High byte Low byte
Register address
Description
8-bit unsigned
16-bit unsigned
32-bit unsigned
32-bit unsigned with reversed register order
32-bit signed with reversed register order
32-bit floating point
64-bit floating point
Time stamp
System time
U16 U32
High data byte High data byte
Low data byte 2nd data byte
– 3rd data byte
– Low data byte
1 2
– 16 15 –
High byte
Register address +1
5
FP32
1st data byte
(sign bit)
2nd data byte
3rd data byte
Last data byte
2
8 7 – 0
Low byte
31