Mitsubishi Electric FR-A820-00046 Instruction Manual page 998

Ethernet communication (FR-A800-E)
Error response
● An error response is returned if the query message received from the master contains an illegal
function, address or data.
No response is returned for parity, overrun, framing, and busy errors.
● Error response (Response message)
³
Transaction
identifier
H
(8 bits)
Message
³ Transaction identifier
· Protocol identifier
» Length field
¿ Unit identifier
´ Function
² Exception Code
Tab. 5-377: Description of response data
● Error code list
Code
01
02
03
06
Tab. 5-378: Error code list
An error response is not returned in the following cases:
– Function code H03 (read data of holding register)
When the number of registers is specified as one or more and there are one or more
holding registers from which data can be read.
– Function code H10 (write data to multiple holding registers)
When the number of registers is specified as one or more and there are one or more
holding registers to which data can be written.
In other words, when function code H03 or H10 is used and multiple holding registers are accessed,
an error response is not returned even if a non-existent holding register or holding register that
cannot be read or written is accessed.
NOTE An error response is returned if none of the accessed holding registers exist. When an accessed
holding register does not exist, the read value is 0 and the written data is invalid.
5 - 796
·
Protocol
identifier
L H L
(8 bits) (8 bits) (8 bits)
Description
The master adds the data for the purpose of transaction control.
The same data is returned in the response from the slave.
Fixed to 0. (When the slave receives data other than 0, it does not send the response
message.)
0 is returned in the response from the slave.
The data length from the unit identifier to the data is stored in byte.
Fixed to 255
The function code requested by the master + H80 is set.
The codes in the following table are set.
Error Item
ILLEGAL FUNCTION
ILLEGAL DATA ADDRESS
ILLEGAL DATA VALUE
SLAVE DEVICE BUSY
» ¿
Length field Unit identifier
H L
(8 bits)
(8 bits) (8 bits)
Error description
The query message from the master is set with a function code that cannot be
handled by the slave.
The query message from the master is set with a register address that cannot be
handled by the slave.
(No parameter, parameter cannot be read, parameter cannot be written)
The query message from the master is set with data that cannot be handled by
the slave.
(Out of parameter write range, a mode is specified, other error)
The request message cannot be processed because the slave is executing
another operation.
Parameters
´ ²
Function Exception code
H80 + Function
(8 bits)
(8 bits)