Mitsubishi Electric Melsec QJ71LP21 Reference Manual page 257

7 APPLICATION FUNCTIONS
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POINT
(1) When simultaneously accessing multiple other stations from the host station,
change the channel setting of the host station for each request target.
Channel 1: Write to station No.1
Channel 2: Read from station No.1
Channel 3: Write to station No.2
Channel 4: Read from station No.2
(2) When accessing other stations with the same channel No. specified, make the
next other station access after completion of the preceding access.
The completion status can be confirmed with the completion device of the link
dedicated instruction.
When the next access is attempted before completion of the preceding access
to another station, the link dedicated instruction issued later is not executed.
(3) When making access mutually between the host station and another station,
change the channel of the host station for each link dedicated instruction.
SEND
Channel 1: For send
RECV
Channel 3: For receive
(4) Up to eight instructions are executable at the same time if no duplication is
found in the channel Nos. (1 to 8) specified in the control data of the
instructions.
REMARKS
Do not use the same channel for link dedicated instructions of both the scan
execution program and the interrupt program.
If a channel is being used for a link dedicated instruction of the scan execution
program, the channel is not available for another link dedicated instruction of the
interrupt program.
The instruction of the interrupt program is put in the wait status at this time, and will
be executed at the next scan timing in this case.
If the link dedicated instruction of the interrupt program precedes that of the scan
execution program, however, the latter cannot be executed because the next scan
timing does not exist in the interrupt program.
Station No.3
(Host station)
Channel 1
Channel 2
Channel 3
Channel 4
Station No.1 Station No.2
(Host station) (Other station)
Channel 1 Channel 1
Channel 3 Channel 3
MELSEC-Q
Station No.1
(Other station)
WRITE
READ
Station No.2
WRITE
(Other station)
READ
RECV
Channel 1: For receive
SEND Channel 3: For send
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