RKC INSTRUMENT Z-TIO-G, Instruction Manual

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7. MODBUS
7-2
IMS01T28-E4
7.1 Communication Protocol
The master controls communication between master and slave. A typical message consists of a request
(query message) sent from the master followed by an answer (response message) from the slave (SRZ).
When master begins data transmission, a set of data is sent to the slave in a fixed sequence. When it is
received, the slave decodes it, takes the necessary action, and returns data to the master.
Data send/receive state can be monitored by using our communication tool (PROTEM2).
The communication tool (PROTEM2) can be downloaded from the RKC official website:
https://www.rkcinst.com/.
7.1.1 Message format
The message consists of four parts: slave address, function code,
data, and error check code which are always transmitted in the
same sequence.
 Slave address
The slave address is a number from 0 to F manually set at the module address setting switch located at the
front of the function module (Z-TIO and Z-DIO).
For details, refer to 3.1 Module Address Setting (P. 3-2).
Although all connected slave units receive the query message sent from the master, only the slave with the
slave address coinciding with the query message will accept the message.
 Function code
The function codes are the instructions set at the master and sent to the slave describing the action to be
executed. The function codes are included when the slave responds to the master.
For details, refer to 7.1.2 Function code (P. 7-3).
 Data
The data to execute the function specified by the function code is sent to the slave and corresponding data
returned to the master from the slave.
For details, refer to 7.2 Register Read and Write (P. 7-8), 7.3 Data Processing Precautions
(P. 7-12) and 8. COMMUNICATION DATA LIST (P. 8-1).
 Error check
An error checking code (CRC-16: Cyclic Redundancy Check) is used to detect an error in the signal
transmission.
For details, refer to 7.1.5 Calculating CRC-16 (P. 7-5).
Slave address
Function code
Data
Error check CRC-16
Message format