Siemens 9410DC, User Manual, Page: 55 / 172

Communications 9410 series
Modbus data classes
Class Description
Coils Digital bits that can be read and written to
Input status Digital bits that can be read
Input registers 16-bit integers that can be read
Holding registers 16-bit integers that can be read and written to
Modbus data formats
Format Type # of Modbus registers used
Unsigned 16-bit Integer 1
Signed 16-bit Integer 1
Unsigned 32-bit Integer 2
Signed 32-bit Integer 2
Unsigned 32B-M10K Integer 2
Signed 32B-M10K Integer 2
IEEE float 1 Floating point 2
Packed Boolean for inputs Integer 1
Packed Boolean for coils Integer 1
Unsigned 16-bit read/write Integer 1
Signed 64 bit Integer 4
1 Meters acting as Modbus masters support two versions of IEEE float with different word orders: high/
low = Big Endian, low/high = Little Endian.
16-bit data (one word) is transmitted with most-significant byte first and least-
significant byte second.
32-bit data (two words) is transmitted with the most-significant word first and the least-
significant word second.
Modbus function codes
Function Description Master/slave
1 Read coil status Master and slave
2 Read input status Master and slave
3 Read holding registers Master and slave
4 Read input registers Master
5 Write to a coil Master
6 Write to a holding register Master and slave
15 Write to multiple coils Master
16 Write to multiple holding registers Master and slave
17 Report slave ID (serial only) Master and slave
43 (subcode 14) Read device identification Master and slave
100 Read scattered holding registers Master and slave
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