Valentin,

If the frequency you use is 11.0592 MHz then one clock pulse is 1/11.0592x10e6 ns (or ~90 ns)

If the frequency you use is 12 MHz then one clock pulse is 1/12x10e6 ns (or ~83 ns)

The frequency can vary anywhere within the valid specification for the 8051 derivative you are using. The chip does NOT divide the frequency, it bases its operation on a state: a state is two pulses. These states are used to create a machine cycle: 6 states equal one machine cycle (one machine cycle equals a total of 12 clock pulses).

It is the pulse width that matters not whether the oscillator frequency is evenly divisible by 12.

The problem is to select the correct value of capacitors to have your crystal oscillate atthe required 11.0592 MHz. I am trying to get my 8051 to communicate with my PC using RS232, so I am in the same boat as you.

Does anyone have the details about the caps? I am still searching. It has been a long, long time since I designed oscillators.