D-Link DE-805TP - 10Mbps Ethernet Mini Hub User Manual download pdf (Page 13)

Modbus for Field Technicians

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message there is no way of telling whether you are looking at two

consecutive 16 bit words, or two consecutive words that should be

interpreted as floating point, long or MK10 formats. Because of this you

always have to look to the vendor docs.

Read more in Appendix 3.

5. FLOATING POINT NUMBERS IN MODBUS

Modbus was not designed to transport floating point numbers. After the

protocol was released and in use – some people came up with a scheme to

using two consecutive 16 bit registers to transport one floating point number.

The scheme is essentially a set of rules for interpreting the bits in the 2x

registers as the elements of a floating point number (like a mini protocol).

Other people came up with other schemes.

One of these schemes has come to dominate. It is called standard IEEE754.

Some devices (servers) do not support floating point numbers.

Many clients (masters) do not support floating point numbers.

A master and a server must use the same floating point scheme to work

together.

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D-Link DE-805TP - 10Mbps Ethernet Mini Hub User Manual Page 13