继续学习ABB 800xA配置手册第一章功能和组件，进入第169页。

An ordinary (non-time-critical) task can be interrupted:

普通（非时间关键型）任务可以中断：

• at the start of any code block. 在任何代码块的开始
• at backward jumps, for example for, while, repeat statements. A time-critical task has special properties. 在向后跳转时，例如，for, while，重复语句。时间关键型任务具有特殊属性。
• The task is not driven by the same scheduler as the rest of the tasks. Instead, the task is driven from the system’s real-time clock (hence the high precision).  该任务与其他任务不由同一计划程序驱动。相反，任务由系统的实时时钟驱动（因此精度很高）。
• The tasks have high precision in execution time. The resolution is 1 ms.  这些任务在执行时间上具有很高的精度。分辨率为 1 毫秒。
• A change to/from time-critical priority in Online mode is not possible.  在联机模式下，无法更改时间关键优先级。
• A change to/from time-critical priority in Offline mode requires re-compilation of the application.  在脱机模式下，对时间关键优先级的更改需要重新编译应用程序。

Consider the following points, when using the time-critical priority.

使用时间关键优先级时，请考虑以下几点。

• Only one time-critical task per controller is allowed.  每一个控制器只允许有一个时间关键任务。
• The execution time for a time-critical task (priority 0) must not exceed 100ms. This restraint prevents the task from blocking other functions, for example communication. 时间关键型任务（优先级 0）的执行时间不得超过 100 毫秒。这种约束可防止任务阻塞其他功能，例如通信。
• All functions cannot be called from the program connected to the task. You cannot set time-critical priority if the code contains invalid instructions (this is checked during compilation). The time-critical task interrupts execution at any time, which means that execution might be interrupted mid-statement. 不能从连接到任务的程序调用所有函数。如果代码包含无效指令，则无法设置时间关键优先级（在编译期间检查）。时间关键型任务随时会中断执行，这意味着执行可能会在语句中途中断。
• If a power failure occurs while the time-critical task is running, the execution of the current code block is completed (assuming that it can be completed within 1 ms). For a warm start to be possible, no code block in the time-critical task may take more than 1 ms to execute. 如果在时间关键性任务运行时出现电源故障，当点代码的执行完成（假设在1ms内可以完成）。为了实现热启动，时间关键型任务中的任何代码块的执行时间都不得超过 1 毫秒。

Task priorities 1–5 can be set by using the firmware function SetPriority. This function is located in the System folder.

任务优先级1-5可以通过使用固件函数SetPriority设置。此函数位于系统文件夹内。

• In HI controller VMT has the highest possible task priority. SIL3, SIL2 and non-SIL can not share the same priority and have the priority in order listed.  在HI控制器，VMT有最高任务优先级。SIL3和SIL2和非SIL不能共享相同的优先级，也不能按照顺序列出优先级。
• Only one task can be connected to a SIL3 application. If more than one task is connected, compilation error is generated. To download remove all tasks except SIL3 task.  一个SIL3应用程序只能连接一个任务。如果连接了多个任务，会产生编译错误。要下载，请删除除 SIL3 任务之外的所有任务。
• The SIL3 tasks must have higher priority than non-SIL and SIL1-2 tasks in the controller. If not compilation error is generated. Decrease the priority of the non-SIL and SIL1-2 tasks or increase the priority of the SIL3 task to enable downloading. SIL3 任务的优先级必须高于控制器中的非 SIL 和 SIL1-2 任务。否则，将生成编译错误。降低非 SIL 和 SIL1-2 任务的优先级，或提高 SIL3 任务的优先级以启用下载。
• It is not recommended to have a task with the same or higher priority than the VMT task, regardless of SIL level. If the VMT task is not the only task with the highest priority, a compilation warning is generated. The user should decrease the priority of any task (SIL or non-SIL) which has the same, or higher priority than the VMT task. 无论 SIL 级别如何，都不建议将任务的优先级与 VMT 任务相同或更高。如果VMT任务不是唯一具有最高优先级的任务，则会生成编译警告。用户应降低与 VMT 任务具有相同或更高优先级的任何任务（SIL 或非 SIL）的优先级。
• Firmware functions that tries to manipulate task parameters from 1131 code does not work for SIL tasks that is SetPriority and SetIntervalTime.  尝试从 1131 代码操作任务参数的固件函数不适用于 SetPriority 和 SetIntervalTime 的 SIL 任务。
• Higher prioritized tasks cannot interrupt a lower prioritized task during IAC fast data copy in/out. If the number of Communication Variables in lower prioritized SIL task exceeds the limits defined in Communication Variable Limits Dialog, then either perform a proper task tuning such that the high priority of the task is not crucial or increase the accepted latency.  优先级较高的任务不会在 IAC 快速数据复制期间中断优先级较低的任务。如果较低优先级的 SIL 任务中的通信变量数量超过“通信变量限制”对话框中定义的限制，则执行适当的任务调整，使任务的高优先级不重要，或者增加可接受的延迟。