Precautions - Mitsubishi Electric MELSEC Q Series User Manual

22.4

Precautions

(1) Opening and closing of communication lines
Execute the opening and closing (mdOpen function/mdClose function) processing of the communication lines at
the start (task startup) and end (task end) of each user program.
Repeating opening and closing for each communication impairs communication performance.
(2) Dummy access
Execute the dummy access to the communication target CPU module before starting access required for control
(In case of the first access to CPU modules by the task, the function execution time may be prolonged).
In addition, if there are multiple target CPU modules, execute dummy access to all CPU modules.
(3) Execution of functions in multiple tasks
Execute opening and closing of the communication lines in (1) in each task. A path acquired by the mdOpen
function cannot be shared among tasks.
(4) Number of communication target CPU modules
The number of CPU modules to be accessed by each task must be set to 8 or less. Otherwise, the
communication performance may be impaired.
(5) Occurrence of stop error
When stop error occurs on the C Controller module, do not access to the station using the block data assurance
per station of the network.
(6) Occurrence of communication timeout
If a communication timeout occurs, adjust the timeout time in "CCPU Parameter"  <<MELSEC data link function
settings>> in Setting/monitoring tools for the C Controller module.
(7) Access to host or another station of the network module
Create a user program to read/write data after ensuring the following conditions so that data reading/writing is
allowed.
If the following conditions are met, data become valid. However, reading/writing functions may complete normally
even when the conditions are not valid.
(a) CC-Link module
Host station device access
• Module error (Xn0) is off (normal)
• Module ready (XnF) is on (operable)
• Own station link status (Xn1) is off (in data link)
Access to another station device and remote operations of another station programmable controller CPU
The following condition is added to the  conditions.
• Data link status of the access target station (Bits corresponding to a communication target station of SW80
to 83, which are read from the own station) is off (normal communication).
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