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8052 - Atmel's 89S52 Port 3 Source/Sink

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wuchy143

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Hi All,

I have exhausted the datasheet and am being ignored by Atmel currently so I figured I'd check on here if anyone had the information I need.

My problem is that I have an 89S52 microhttps://www.keil.com/dd/docs/datashts/atmel/at89s52_ds.pdf and I'm driving an LED(1 mA of current) on the P3.3 port pin. It's one of the interrupt pins but was the only one available for me to use in my design. When I do this the port pin p3.3 can only drive up to about 3V. Then when I disconnect the bias resistor it's able to drive to 5V just fine.

It says in the datasheet that port 3 is capable of sourcing/sinking current. Though, I couldn't find the max current it can supply. I think I may not be able to provide the correct current to the LED which is then bringing my voltage down to 3v but would like to know more about the 89S52 before I can say that for sure. Anyone know anything about port 3?

Thanks

-mike
 
yeh I saw that too but wasn't sure that it means any pin on port3 or just a select few. My F.W guy is out today so I'm going to have him look at the code and see what's it's doing with that port pin. The thing that blows me away is that when disconnected from the LED that pin goes high to +5V like it should. I even looked at the signal on my scope and it's not a digital signal. It's a clean 3V. Weird.

Thanks
 
Just remember that even though you can sink 15mA on a single pin on port C there is a maximum of 71mA for all output ports in total..

consider an LED at 15mA will have a voltage drop of about 2v, so if you use a 220 ohm resistor the LED will run about 13mA.

Cheers Ian

Actually running through the data sheet its only 10mA per pin and a total of 15mA for the whole of port C.
so use a 330 ohm resistor
 
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