Mitsubishi Electric QJ71MB91 User Manual page 71

4
MODBUS STANDARD FUNCTIONS
(2) When the processing is completed in error at the slave (QJ71MB91)
When the processing (read/write, diagnostics, etc.) requested by the request
message is completed in error, an exception code is sent to the master.(
"Response message formats (when completed with an error)" in Section 4.4 to 4.20.)
(a) Storage location of exception code and error code
(3) How to see the request/response message formats provided in Section
4.4 to 4.20
(a) Request/Response message format diagram
[For request message format]
Setting range
[For response message format]
Value stored to the
response message
The exception code is also stored in the buffer memory of the QJ71MB91.
Furthermore, for identification of detailed causes, an error code is stored in the
QJ71MB91 buffer memory.
The exception code and error codes can be confirmed by the error log area of the
buffer memory (address: 0CFE
The following shows how to see the request/response message format diagrams
provided in Section 4.4 to 4.20.
Area name
Function code
Function
Frame contents
code
(01
1 byte (8 bits)
Figure 4.7 Request/Response message format diagram
to 0DFF ).( Section 11.4)
H H
Head coil number
(0000 to FFFF )
H H
)
H
(L)
(H)
1 byte (8 bits)
. . .
4.3 Protocol Data Unit Formats by Functions
Data
Read points
(0001 to 07D0 )
H H
(L)
(H)
When a single data is expressed
by 2 bytes, set the upper byte
(8 bits) as (H) and the lower byte
(8 bits) as (L).
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