Considerations - Mitsubishi Electric MELIPC MI5000 Series Programming Manual

Considerations

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The following shows the considerations when using the MELSEC data link functions.
Considerations for programming
■Open/close processing of a communication line (mdOpen/mdClose function)
Perform the open/close processing of communication line (the mdOpen/mdClose 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 mdOpen function
At the first execution of the function after using the mdOpen function, it takes longer to execute the function since the CPU
module or MELIPC information needs to be acquired. The succeeding processing time can be shortened by performing
dummy access the first time.
■Count of access to other stations from the same task
Accessing 33 or more other stations simultaneously on the same task of a MELIPC 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.
■taskDelete execution
Do not execute the taskDelete in a task using the MELSEC data link function. Also, do not delete a task using the MELSEC
data link function with the taskDelete. Otherwise, the MELSEC data link function may not operate properly.
Considerations during device access via CC-Link IE Field Networks
An interlock may be required to be provided depending on the link status of the own station and other stations.
■Access to devices on the own station
Create a user program that provides an interlock to enable data reading/writing only when the bit of data link error status of
own station (Jn\SB0049) is OFF (normal) and cyclic transmission status (a bit corresponding to the communication target
station which is stored to any of Jn\SW00B0 to Jn\SW00B7) is '0' (data link normal station). However, read or write processing
for the own station will successfully complete even if the conditions are not satisfied.
■Other station transient access (other station remote operation and device access)
Create a user program that provides an interlock to access only when the bit of the baton pass status of the own station
(Jn\SB0047) is OFF (normal) and a baton pass status of the station to be accessed (a bit corresponding to the communication
target station which is stored to any of Jn\SW00A0 to Jn\SW00A7) is '0' (baton pass normal station).
Considerations on interrupt service routine (ISR)
The MELSEC data link function cannot be run within an interrupt service routine (ISR). When you want to run the MELSEC
data link function in synchronization with an interrupt, implement a notification process in the user program and perform it in a
task.
1 PROGRAMMING
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1.2 MELSEC Data Link Functions