1 floating-point data, 2 the two 16-bit registers format, Floating point data – Varec 4000 User Manual

Page 61: 6 floating-point registers

4000

Modbus Implementation

9.6

Floating-Point Registers

Although not part of the Modbus protocol specification, floating point numbers have been implemented using the IEEE

754 standard. Floating point numbers reduce the complexity required in scaling integer values and provide a means

to transmit numbers used by the ATT that are not easily scaled (such as the scaling factors themselves).

9.6.1

Floating-Point Data

The ATT is capable of using a two 16-bit registers format and a one 32-bit register format. Examples and descriptions

of both formats follow.

Note!

Although this type of data does not require scaling, it is important that the measurement unit selected in the ATT be
the same as that expected by the host. In addition, where possible, data is available in both integer and floating-point
formats.

9.6.2

The Two 16-bit Registers Format

Function code 03 or 04 is used to read floating-point registers in this format. Function code 16 is used to write

floating-point registers in this format. An example of reading the temperature, register 102 ( 0066 Hex), in floating-

point format from the ATT is shown as follows:

9.6.3

Floating Point Data

•

Hexadecimal representation: 42 C8 00 00

•

Decimal equivalent: 100.00

Floating-point registers that are defined as reserved have zero (0) as their only legal value. A write command to a

reserved floating-point register is ignored.

Host Request
Address

Function

Code

Start Reg
H

Start Reg
L

# of Reg
H

# of Reg
L

Error
Check

ATT Response
Address

Function

code

Byte

Count

Data
MSB

Data
LSB

Data
MSB

Data
LSB

Error
Check