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The highest frequency that can be counted of AT89S51?

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New Member
I make a 2-channel AT89S52-based frequency counter (Microcontroller for better live: Microcontroller-based 2 Channel Frequency-Meter). I use timer 0 and 1 as counter. Referred to the datasheet, the timer can count the maximum incoming frequency at 1/12 of clock frequency operation. In fact, if we use 12 MHz clock frequency, it only can count maximum 912 kHz incoming frequency. If we change the clock frequency to 24 MHz, it only can count maximum 912 kHz incoming frequency too. Whereas, referred to the datasheet, the maximum incoming frequency should up to 2 MHz (1/12 of 24 MHz).
Why the incoming maximum frequency 912 kHz?
Please, give me an explanation!
How can we build a 2 MHz AT89S52-based frequency counter?


Well-Known Member
I went to the link and found out that the part is already running a 24 MHz. I'm guessing it has to do with the way ATMEL implements double speed operation, with selectable dividers all over the place to maintain compatibility with the original architecture.

Have you read the ATMEL datasheet very very carefully to know if this is possible?
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