Communications
11.5 Modbus RTU/ASCII Protocol
BW500 and BW500/L
146 Operating Instructions, 12/2016, A5E33482052-AD
Bit Mapped bits are packed into registers in groups of 16 bits (1 word). In this manual we
number the bits from 1 to 16, with bit 1 being the least significant bit and bit 16 referring to the
most significant bit.
Large numbers are put into unsigned 32 bit integers with a fixed decimal place of three. For
example, a value of ‘7345’ represents a value in the BW500 ‘7.345’. The default word order is
that the first word is the most significant word (MSW) and the second word (register) is the least
significant word (LSW).
For example, if we read R41,431 as a 32-bit, the 32 bits would look like the following:
32 32-bit integer value (UNINT32) 1
The whole is read as a 32-bit integer. The most significant byte (MSB) and least significant byte
(LSB) can be reversed to accommodate some Modbus drivers.
If a Siemens Milltronics device parameter returns a text message, that message is converted to
a number and provided in the register. The numbers are shown in the table below:
Text Message as Displayed on LCD
(parameter does not exist)
value is less than -20,000
value is greater than 20,000
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