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Communication operation and setting
Error response
An error response is returned if the query message received from the master has an illegal function, address or data.
No response is returned for a parity, CRC, overrun, framing or busy error.
Error response (Response message)
Error code list
An error will not occur in the following cases.
1)Function code H03 (Read holding register data)
When the No. of Points is 1 or more and there is one or more holding registers from which data can be read
2)Function code H10 (Write multiple holding register data)
When the No. of Points is 1 or more and there is 1 or more holding registers to which data can be written
Namely, when the function code H03 or H10 is used to access multiple holding registers, an error will not occur if a non-existing holding register
or read disabled or write disabled holding register is accessed.
Message data mistake detection
To detect the mistakes of message data from the master, they are checked for the following errors.
If an error is detected, a trip will not occur.
Error check item
NOTE
No response message is sent in the case of broadcast communication also.
1) Slave
Address
2) Function 3) Exception Code CRC Check
(8 bits)
H80 + Function
(8 bits)
(8 bits)
L
(8 bits)
H
(8 bits)
Message Setting Description
1) Slave Address Address received from the master
2) Function Master-requested function code + H80
3) Exception Code Code in the following table
Code Error Item Error Description
01 ILLEGAL FUNCTION
The set function code in the query message from the master cannot be
handled by the slave.
02 ILLEGAL DATA ADDRESS
The set register address in the query message from the master cannot be
handled by the drive unit.
(No parameter, parameter read disabled, parameter write disabled)
03 ILLEGAL DATA VALUE
The set data in the query message from the master cannot be handled by the
drive unit.
(Out of parameter write range, mode specified, other error)
REMARKS
An error will occur if all accessed holding registers do not exist.
Data read from a non-existing holding register is 0, and data written there is invalid.
Error Item Error Description Drive unit Operation
Parity error
The data received by the drive unit differs from the
specified parity (Pr.120 setting).
1)Pr.343 is increased by 1 at error
occurrence.
2)The terminal LF is output at error
occurrence.
Framing error
The data received by the drive unit differs from the
specified stop bit length (Pr.120).
Overrun error
The following data was sent from the master before
the drive unit completes data receiving.
Message frame error
The message frame data length is checked, and the
received data length of less than 4 bytes is regarded
as an error.
CRC check error
A mismatch found by CRC check between the
message frame data and calculation result is
regarded as an error.