Lpc2000

Thank you Peter for your answer.

We're used to worst-case-dimensioning, that's why I was interested 
into that data (that you can often find on other micros manuals).

After all, the worst situation is 26 port out of 32 sinking 2mA each, 
total about 52mA for the entire port. Should be safe.

RL



--- In lpc2000@yahoogroups.com, Peter Jakacki <peterjak@t...> wrote:
> 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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