4 - 17 4 - 17
MELSEC-Q
4 MODBUS
R
STANDARD FUNCTIONS
4.3.10 Write file record (FC: 21) (SC: 06)
Writes values to one or more extended file registers.
Number of accessible devices with one message
1 to 122 points
(1) Request message format (Master Slave)
Number of
bytes
m 7
Data
File number
(0000
H
to FFFF
H
)*
(H)
(L)
Function code
Function code
(15
H
)
Write head
device number
(0000
H
to 270F
H
)
(H)
(L)
(H)
(L)
Sub-request 1
Reference
number
(06
H
)
Write points
n1
(0001
H
to 007A
H
)
(Number of bytes m 7)
(Number of bytes m 7)
Device data
1
Device data
n1
(H)
(L)
(H)
(L)
Data
File number
(0000
H
to FFFF
H
)*
(H)
(L)
Write head
device number
(0000
H
to 270F
H
)
(H)
(L)
(H)
(L)
Reference
number
(06
H
)
Write points
nm
(0001
H
to 007A
H
)
Device data
1
Device data
nm
(H)
(L)
(H)
(L)
Sub-request m
: The upper limit of the file number available for the QJ71MT91 slave function is
equal to the file register size of the mounted programmable controller CPU.
(Refer to Section 7.4.4.)
(a) Specify the total write points of all the sub-requests, N (n1 +
+ nm) so
that the size of the PDU (protocol data unit) in the request message does
not exceed 253 bytes.
2 + m 7 + N 2 253
If the above condition is not satisfied, the request message is discarded.
