AT89S52-24PC Symbol Parameter Min Max Units 1/t CLCL Osc Frequency 0 33 MHz t CLCL Clock Period 30 ns t CHCX High Time 12 ns t CLCX Low Time 12 ns t CLCH Rise Time 5 ns t CHCL Fall Time 5 ns AT89C52-20PC Symbol Parameter Min Max Units 1/t CLCL Osc Frequency 0 24 MHz t CLCL Clock Period 41.6 ns t CHCX High Time 15 ns t CLCX Low Time 15 ns t CLCH Rise Time 20 ns t CHCL Fall Time 20 ns