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　1、Beckhoff耦合器 DP Cycle和K-bus cycle的同步

　　參考BK3xx0.chm -> PROFIBUS DP Communication -> Cyclic Data Exchange -> K-Bus Cycle

　　K-bus分為2種模式工作： FreeRun / Synchronous

　　● FreeRun (與DP Cycle無關)

　　FreeRun又分為Slow和Fast兩種模式。

　　Slow FreeRun：It is a characteristic feature of the Slow FreeRun mode that the K-Bus cycle is called from the main task. Acyclic communication or events result in heavy jitter in the K-Bus cycle (KS2000, DPV1, terminal diagnosis, etc.), because all of these functions are also called from the main task.

　　Fast FreeRun：The K-Bus cycle is called under time control from a high priority task. Following completion of the K-Bus cycle, the lower priority tasks (DPV1, KS2000 interface, etc.).

　　如圖，與slow freerun模式相比，fast的k-bus執行有更為固定的循環周期。