Data Formats; Command Frames; Section 4 Modbus Communications Protocol - Omron KM50 Communications Manual

Section 4 Modbus Communications Protocol

4. 1 Data Formats

Frames that comply with the Modbus RTU communications protocol are used as the unit of data
for commands from the host (e.g., a computer) and responses from the KM50-C/-E. The format of
command frames and response frames is given below.
In this manual, numbers followed by "hex," such as "02 hex," are hexadecimal numbers.
Alphanumeric characters that are given in quotation marks, like this "00," are ASCII characters.

■ Command Frames

When using RTU mode, start with a silent interval of at least 3.5 characters and end with a silent
interval of at least 3.5 characters.
Slave Function
address code
Silent interval of 3.5 characters min.
Specify the unit number.
The slave address can be set to between 00 and 63 hex (0 and 99).
Slave address
Specify 00 hex for broadcasting.
Responses are not returned for broadcast command frames.
The function code is a 1-byte hexadecimal code that indicates the type of
Function code
command sent from the host (e.g., a computer).
This is the text data that is associated with the specified function code.
Data Specify the required data, such as the variable address, parameter
setting, etc. (Set the hexadecimal.)
Cyclical Redundancy Check: This check code is calculated with the data
CRC-16 from the slave address to the end of the data.
The check code is 2-byte hexadecimal.
Silent interval of 3.5 characters min.
4-2
Data
CRC-16 calculation range
CRC-16
2 bytes