Mitsubishi Electric A800-E Instruction Manual page 48

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)
a.
b. Protocol
Transaction
identifier
identifier
H L H L
(8 bits) (8 bits) (8 bits) (8 bits)
Message
a Transaction identifier
b Protocol identifier
c Length field
d Unit identifier
e Function
f Exception code
• Error code list
Code Error item
01 ILLEGAL FUNCTION
02 ILLEGAL DATA ADDRESS
03 ILLEGAL DATA VALUE
06 SLAVE DEVICE BUSY

An error response is not returned in the following cases:
 Function code H03 (reading data of holding registers)
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 (writing 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
nonexistent holding register or holding register that cannot be read or written from/to 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.
(N) Operation via communication and its settings
c. Length d. Unit
field identifier
H L
(8 bits)
(8 bits) (8 bits)
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.
The query message from the master has a function code that cannot be handled by the
slave.
The query message from the master has 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 has 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.
e. Function f. Exception code
H80 + Function
(8 bits)
(8 bits)
Description
Error description
47
PARAMETER
2
GROUP
N