1.
If you build some logic within a CPLD then its many more reliable to synchronize all asynchroneous inputs with a master clock.

Otherwise you have no control, how long / short the generated pulse duration was.
And if you feed a pulse into a counter, which meet not the needed minimum duration, this counter reacts totally crazy.
Also some metastable effects can occur.


2.
Since today most sensors contain a µC and sends the output value over busses like RS-485 or CAN, there is no need to waste extra hardware for a job, which can easiliy be done inside the µC.

E.g. I use the T89C51CC01 to read out two sensors and feed the 4 signals into 4 inputs of the capture unit. The I get an interrupt on every change of one of the 4 inputs and count up/down the X/Y counter values.



Peter