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    ttl input sink

    In the AT89C51 datasheet, I don't understand the following statemment:
    Port 3 can sink/source 4 TTL inputs.
    Thanks

    •   Alt7th July 2006, 21:36

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    at89c51 fan-in

    Goto: http://www.st-andrews.ac.uk/~jcgl/Sc...logic/TTL.html
    and take a look at "Basic Properties of some TTL Families" ..
    If, for example, "0 Level Input Current" for each TTL input is 1.6mA that means that the microcontroller pin can sink more than 4*1.6mA of current if it wants to generate an "L" on these inputs ..
    Similar story with "1" but this time a pin will not sink but source current for at least 4 TTL inputs (> 4 * 0.04mA) ..

    Regards,
    IanP



    •   Alt8th July 2006, 02:17

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    AT89C51 Port 3 can sink/source 4 TTL inputs.

    It tells that the fan-in & fan-out capability of the port is 4.



    •   Alt8th July 2006, 05:52

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    Re: AT89C51 Port 3 can sink/source 4 TTL inputs.

    please what is meant by fan-in fan-out?



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    Re: AT89C51 Port 3 can sink/source 4 TTL inputs.

    fan-out
    Fan-out is a term that defines the maximum number of digital inputs that the output of a single logic gate can feed. Most transistor-transistor logic (TTL) gates can feed up to 10 other digital gates or devices. Thus, a typical TTL gate has a fan-out of 10.
    quoted from:
    http://whatis.techtarget.com/definit...927615,00.html

    Regards,
    IanP


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