Vaisala MMT330 - Manual (Page 164)

User's Guide _______________________________________________________________________
164 __________________________________________________________________ M210764EN-F
Register Map
All data available via the Modbus interface is grouped in six contiguous
blocks of registers as described in Table 34 below.
Table 34 MMT330 Modbus Register Blocks
Address Data Format Description
0001…0068 32-bit IEEE float Measurement data (read-only)
0257…0290 16-bit signed integer
0513…0517 Bit field Status registers (read-only)
0769…0790 32-bit IEEE float Configuration settings
1025…1035 16-bit signed integer
1281…1288 Bit field Configuration flags
The addresses are 1-based decimal Modbus data model addresses without
the first digit (e.g. 0xxxx, 1xxxx, 3xxxx, or 4xxxx). Subtract 1 to get
address field values used in Modbus Protocol Data Unit (PDU).
The register map is the same for all Modbus function codes. For
example, function codes 03 and 04 return exactly same result, as do
01 and 02.
Function codes 01 and 02 return 0 if the corresponding register has value
0x0000 and 1 if the register is non-zero. Writing with function codes 05
or 15 effectively writes value 0x0000 or 0x0001 in the register(s).
Data Encoding
All numeric values are available both in 32-bit IEEE floating point and
16-bit signed integer formats.
32-Bit Floating Point Format
Floating point values are represented in standard IEEE 32-bit floating
point format. Least-significant 16 bits of floating point numbers are
placed at the smaller Modbus address as specified in Open Modbus TCP
Specification, Release 1.0. This is also known as “little-endian” or
“Modicon” word order.
NOTE Despite the specification, some Modbus masters may expect
“big-endian” word order (most-significant word first). In such case, you
must select “word-swapped” floating point format in your Modbus
master for MMT330 Modbus registers.
A “quiet NaN” value is returned for unavailable values. Writing any NaN
or infinite value is silently ignored. A quiet NaN is, for example,
0x7FC00000; however, the master should understand any NaN value.