APPENDIX. HOST COMMUNICATION PROTOCOL
IMR02E20-E1
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A.3.4 Slave responses
(1) Normal response
In the response message of the Read Holding Registers, the slave returns the read out data and the
number of data items with the same slave address and function code as the query message.
In the response message of the Preset Single Register, the slave returns the same message as the
query message.
In the response message of the Diagnostics (Loopback test), the slave returns the same message as
the query message.
In the response message of the Preset Multiple Registers, the slave returns the slave address, the
function code, starting number, and number of holding registers in the multi-query message.
(2) Defective message response
If the query message from the master is defective, except for
transmission error, the slave (SRZ unit) returns the error response
message without any action.
Example:
If there is a problem in the data range of CH3 when writing data of four
channels, the data of CH1 and CH2 will be written. The data of CH3 and
CH4 will be disregarded and an error response message will be returned.
If the self-diagnostic function of the slave (SRZ unit) detects an
error, the slave (SRZ unit) will return an error response message to
all query messages.
The function code of each error response message is obtained by
adding 80H to the function code of the query message.
Error code
Contents
1
Function code error (An unsupported function code was specified)
2
When the mismatched address is specified.
3
When the specified number of data items in the query message exceeds the
maximum number of data items available
When the data written exceeds the setting range
4
Self-diagnostic error response
(3) No response
The slave (SRZ unit) ignores the query message and does not respond when:
The slave address in the query message does not coincide with any slave address settings.
The CRC code of the master does not coincide with that of the slave.
Transmission error such as overrun, framing, parity and etc., is found in the query message.
Data time interval in the query message from the master exceeds 24 bit’s time.
Slave address
Function code
Error code
Error check CRC-16
Error response message
