Lpc2000

The terms Iol and Ioh are given as 4ma when refering to Voh and Vol 
logic levels respectively. This simply means the minimum guaranteed 
current that the pin can supply and still maintain a valid logic level. 
Now Ioh and Iol can supply a lot more current if you are not concerned 
about logic levels. So you could drive an LED at 16ma ok but don't 
expect it to maintain a valid logic level. Instead of 0.4V at 4ma you 
may get a >1V "low" when sinking 16ma.

Limiting Values (or Absolute Maximum Ratings) tells you not to expect 
the device to keep smiling when you push it so hard, it might let all 
the magic smoke out. In this respect the absolute max DC current per pin 
is 100ma. That's per pin and doesn't just mean the I/O, but unless you 
actually test the current per pin there is no easy way to know how much.

Another thing, drawing current like that, especially 32-bits switching 
at a time can cause a bit of "ground bounce" where the ground potential 
can rise above 0V, but this is another issue altogether.

To answer your question a bit more specifically then, it does seem 
possible to draw 128ma from 32 pins but this would only be possible if 
the internal grounds ran to more than one pin etc. But good design calls 
for safety margins to cater for all kinds of highly interactive 
conditions. Well there's an exercise for you, measure the currents and 
let us know. I gather it's a 22xx device.

Aesop always had a moral to the story, I guess this could be one:
Respect the limiting values unless you don't care that it might fail. 
Respectfully limit values to take care that it does not fail.

*Peter*

extra300_it wrote:

>The hardware manual says that the maximum current for each GPIO 
>output pin is 4 mA in both directions.
>
>Is there any limitation considering the whole 32-bit port?
>
>That is: 
>Can I draw 4mA from each pin of Port 3, taking a total of 4*32=128mA 
>from P3?
>Or there is a maximum total current for each port?
>


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