Precautions For Programming; Precautions For Program Creation - Mitsubishi Electric MELSEC Q Series User Manual

19.4

Precautions for Programming

The following describes precautions for programming.
19.4.1

Precautions for program creation

(1) Endian format (memory layout)
The endian format (memory layout) of the C Controller module is little endian.
Compile the user program in the little endian format.
(2) VxWorks real-time process (RTP)
The C Controller module does not support applications running in VxWorks real-time process.
Create a user program as an application based on the VxWorks kernel.
(3) User program execution
Execute a user program by starting a task from the script file. ( Page 344, Section 19.6)
The system may malfunction if the user program is executed without a task being started.
(4) Number of tasks (Using Q24DHCCPU-V/-VG)
The number of tasks that can simultaneously execute user programs that use the bus interface function, MELSEC
data link function and C Controller module dedicated function is up to 180.
If over 180 tasks are simultaneously executed, the system may not operate properly.
(5) Startup of a task that performs floating-point operations
Always specify the VX_FP_TASK option for the third argument of taskSpawn when activating a task that:
• Performs floating-point operations
• Calls a function that returns a floating-point value.
• Calls a function that takes a floating-point value as an argument.
If the above task is activated without the VX_FP_TASK option specified, the operating system may run away.
When specifying the VX_FP_TASK option in a script file, refer to the following.
 Page 344, Section 19.6 (2)(b)
For details on the VX_FP_TASK option, refer to the manual for VxWorks.
(6) Execution of the task in STOP or PAUSE status
Even if the C Controller module operation status is STOP or PAUSE, the user program task does not stop.
Use the CCPU_GetCpuStatus function when splitting the user program processing according to the operation
status of the C Controller module.
(7) Access to USB device
To create a program that accesses to a USB device, perform processing to check if access to the USB device is
allowed, and retry.
Though a USB device is automatically mounted when connected, it may take several minutes until it becomes
accessible depending on format types and capacities of the USB device.
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