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4
MODBUS STANDARD FUNCTIONS
4.3.10 Write file record (FC: 21) (SC: 06)
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Writes values to one or more extended file registers.
(1) Request message format (Master → Slave)
1: 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.)
2: N indicates the total number of write points (n1 +
(a) Specify the total write points of all the sub-requests, N (n1 +
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.
Number of accessible devices with one message
1 to 122 points
MELSEC-Q
+ nm).
+ nm)
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