Mitsubishi Electric MELSEC-A Series Manual page 110

2
REPLACEMENT OF MELSECNET (II) AND /B (PLC TO PLC NETWORK)
(3) Sequence program
(a) Data separation prevention
When two words (32 bits) or more of cyclic data are handled, the old data sometimes is mixed with
the new data. To read/write cyclic data of two words or more in a single operation, set data separation
prevention by the following method.
1) Interlock program using BW
Data separation can be prevented by performing handshaking using BW between the cyclic data
sending station and cyclic data receiving station.
The following shows an example of an interlock program for handshaking.
Sending station
1)
2
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When handling data larger than two words (32 bits) at one time without using the 32-bit
data guarantee function or the block guarantee per station function, the data may split
into new and old data coexisting in one word (16 bits) units.
As in the example below, the program should be interlocked using the oldest number
of either the link relay (B).
Receiving station
4)
2)
3)
7)
1) The send command turns on.
2) The contents of D0 to D2 are stored in W0 to W2.
3) Upon completion of storage in W0 to W2, B0 for handshaking turns on.
4) By cyclic transmission, the link relay (B) is sent after the link register
(W), which turns on B0 of the receiving station.
5) The contents of W0 to W2 are stored in D100 to D102.
6) Upon completion of storage in D100 to D102, B100 for handshaking
turns on.
7) When the data is transmitted to the receiving station, B0 turns off.
5)
6)