Varec 4000 manual Floating-Point Registers, Floating-Point Data, Two 16-bit Registers Format

4000 Modbus Implementation

9.6Floating-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).

9.6.1Floating-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.

9.6.2The 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:

Host Request
Address	Function	Start Reg	Start Reg	# of Reg	# of Reg	Error
	Code	H	L	H	L	Check
01	03	00	66	00	02	XX
ATT Response
Address	Function	Byte	Data	Data	Data	Data	Error
	code	Count	MSB	LSB	MSB	LSB	Check
01	03	04	42	C8	00	00	XX

9.6.3Floating 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.

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