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AT89C51 Port 3 can sink/source 4 TTL inputs.

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amrstaha

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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
 

at89c51 fan-in

Goto: https://www.st-andrews.ac.uk/~jcgl/Scots_Guide/datasheets/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
 

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

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


    amrstaha

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