Maximum Input frequency for T0, T1, T2 inputs

Question: What is the maximum frequency for the T0, T1, T2 inputs?

 

Answer:

The maximum  input frequency is 1/8th the frequency of the 8051.  e.g., if 8051 is running at 48 MHz then the max input frequency is 6 MHz.  The minimum pulse width high or low is equal to four 8051 clocks.  e.g., if 8051 is running at 48 MHz then the minimum pulsewidth is 4 * 20.8 nS.