Considerations - Mitsubishi Electric MELSEC iQ-R Series Manual

Considerations

The following shows the considerations when using the MELSEC iQ-R series data link functions.
Considerations for programming
■ Open/close processing of a communication line (mdrOpen/mdrClose function)
Perform the open/close processing of communication line (the mdrOpen/mdrClose function) only once at the start of task
(task activation) and at the end of task (task completion) respectively in each user program. Opening/closing the line every
communication decreases the communication performance.
■ Execution after using the mdrOpen function
At the first execution of the function after using the mdrOpen function, it takes longer to execute the function since the CPU
module information needs to be acquired. The succeeding processing time can be shortened by performing dummy access at
the first time.
■ Access to other stations on the same task
Accessing 33 or more other stations simultaneously on the same task of C intelligent function module using a user program
may decrease the communication performance. To access other stations simultaneously on the same task, limit it to 32 or less
stations.
■ mdrGetLabelInfo function call
The mdrGetLabelInfo function does not need to be called each time to access a target CPU module.
Only if the error occurs (Error code: -81) when accessing by using the mdrRandRLabel/mdrRandWLabel function , call the
mdrGetLabelInfo function again.
■ taskDelete execution
Do not execute the taskDelete in a task using MELSEC iQ-R series data link function. Also, do not delete a task using the
MELSEC iQ-R series data link function with the taskDelete. Otherwise, the MELSEC iQ-R series data link function may not
operate properly.
■ Error by access concentration in a CPU module
When using the MELSEC iQ-R series data link function to access a CPU module from multiple modules or a built-in Ethernet
port of the CPU module in the system where communication processing such as device access to a CPU module is performed
frequently, an error may occur in communication processing on other modules due to the concentration of processing to a
CPU module.
When verifying the operation at the system construction and if an error occurs in communication processing, take a following
measure before running the system.
• When executing the MELSEC iQ-R series data link function in multiple tasks, do not execute the function at the same time
by exclusion control, or execute the function in one task.
• Lengthen the execution interval of the MELSEC iQ-R series data link function to avoid errors in communication processing.
1 COMMON ITEMS
1.3 MELSEC iQ-R Series Data Link Functions
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