Solution:

Regarding to the driver of PCL-836, here're some information. You also can refer to the attached file for further detail information. ================================================================================================== MODE 3: SQUARE WAVE MODE After writing a Control Word and initial count, the Counter will be loaded on the next CLK pulse. This allows the Counter to be synchronized by software also. Writing a new count while counting does not affect the current counting sequence. If a trigger is received after writing a new count but before the end of the current half-cycle of the square wave, the Counter will be loaded with the new count on the next CLK pulse and counting will continue from the new count. Otherwise, the new count will be loaded at the end of the current half-cycle. ================================================================================================== Due to above behave of 8254, so you will see the strange value. For example, using the example "Counter" of 32-bit DLL drivers, the scan period is 10 ms, then you'll see the nonsense value while start polling the count value. Anyway, now the driver (16-bit counter) just response the real value of 8254. It's recommended to add a delay time after initial (start) the 8254. And this delay period is depends on the computer, so the users should adjust this delay time themselves for more higher reliability.