Spectrasensors OXY5500 - Modbus Function Codes and Data Formats

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Oxygen Analyzer

4–2 4900002239 rev. G 7-11-17

Function Codes

Available public functions are:

• 3: Read Holding Registers

• 4: Read Input Registers

• 16: Write Multiple Registers

Please note that function codes 3 and 4 are fully interchangeable as they

behave in the same way.

Data Formats

Float

The Float refers to the floating point according to IEEE 754 (Single Precision).

This format requires two registers obtaining 32 bit where each register contains

the high byte in its first bit.

For example, if the float value is 20.56 (int32), represented as 0x41A47AE1

(hexaint32), it is written in two consecutive registers, where the first register

is 3499. Therefore, the value has to be transmitted in the following way:

Int32

All int32 values are 32bit-wide integer values. The example given in the

previous section applies here as well.

Character

The definition is as follows:

• 8bit ASCII-Code table according to ISO-8859-1 (Latin-1 Western

European)

Function code 16 may be used with broadcast (device ID = 0).

Codes 3 and 4 may not be used with broadcast.