7-9
Chapter 7. Modbus RTU Communication Functions
The data addresses, the number of data, and the data values are expressed using hexadecimal notation.

Hexadecimal
The specifications of hexadecimal numbers are shown in the table below.
If the specifications are not satisfied, this controller returns an error response
without processing the instruction message.
Item Specifications Out of spec examples
Allowable characters 00H to FFH (all)
Number of characters 2 or 1 00H 01H 02H (3 characters)
Expressible numeric
values
(2 characters)
8000H to 7FFFH (signed data)
0000H to FFFFH (unsigned data)
Expressible numeric
values
(1 character)
00H to FFH (unsigned data)
Examples of normal
character strings
00H 00H
12H ABH
01H 23H
FFH FFH
10H
04H
Handling Precautions
• In Modbus communication, numeric values are expressed in order from the
high-order to the low-order (big endian).
7 - 4 Numeric Value Expression
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