It is said that 8051 has an on-chip oscillator but requires external clock to run it. What may be the internal circuit for on-chip oscillator, how it runs after connecting crystal oscillator? Also what is the purpose of external capacitor with crystal oscillator?
Yes I agree. Mazidi is a standard reference book that is recommended by professors in collages and universities.
I am a student and I have just seen two books about 8051 the books are one by Mazidi and the other by Ayala. We students don't know about datasheet and also the teachers at our locality (South Asia) do not possesses enough practical knowledge to illustrate such critical topics. We are limited to theory from these books and some basic simulation on software.Hence the issues need to be brought into notice of the author.