想问一下，在FM350-1中控制程序块FC2中的L_DIRECT是直接装载预置值，L_PREPAR是允许写入预置值，这两个到底区别是在哪呢？

LDIRECT是直接写技术值，L_PREPAR只是将LOAD_VAL写到preparation预置值中，那么预置值什么时候写入计数值？手册上有一段话：
You can load the load value in preparation only (control signal L_PREPAR). A load
value that is loaded in preparation is accepted by the FM 350-1 as a new counter
value in response to the following events:
In the single counting and periodic counting Count modes
– When the upper or lower limit is reached if no main counting direction is set.
– When the set upper counting limit is reached for main counting direction up.
– When 0 is reached for main counting direction down.
In all Count modes
– The counting process is started by the interrupting SW or HW gate (the load
value is not accepted when the counting continues).
– Synchronization
– Latch/retrigger