Modbus Rtu & Ascii Functions; Modbus Floating Point Formats - Thermo Scientific SmartView SV100A User Manual

Modbus RTU &
ASCII Functions
Modbus Floating
Point Formats
Thermo Fisher Scientific
The instrument supports a subset of the Modbus protocol RTU and
ASCII. These functions include:
Table 7-1.
Function # Description
1 Read Coil Status
2 Read Input Status
3 Read Holding Registers
4 Read Input Registers
Note Some registers are reserved or are not used. Use the defined registers
only. ▲
The registers most users will be interested in are the Point 1 through Point
36 Data Registers. These registers hold the current floating point value for
each data point. The original Modbus specification has no mention of
floating point numbers. Therefore, several methods of transferring floating
point numbers have emerged. Thermo Scientific supports two of these
methods. One is compatible with the Modicon 984 PLC and the other is
referred to as the Daniel's Extension. IEEE floating point number requires
4 bytes (2 words). From the original specifications, Modbus registers are all
2 bytes (1 word).
Setting up Communications
Modbus RTU & ASCII Functions
Function # Description
5 Force Single Coil
6 Preset Single Register
15 Force Multiple Coils
16 Preset Multiple Registers
SV100A/SV10AC User Guide 7-7