On 1 Dec 2005, at 23:14, Harold Hallikainen wrote:

>
>>
>> On 1 Dec 2005, at 21:49, Harold Hallikainen wrote:
>>
>>> Of
>>> course at 3.3V, you can't get the 25mA you can get at 5V, but
>>> that's not
>>> the USART's problem.
>>
>> Eh!?  Where does it say that on the datasheet!?  Why of course?
>>
>> Cheers
>>
>> Ed
>
>
> Well... I THOUGHT there were graphs in the datasheet showing source/ 
> sink
> current versus supply voltage, but I sure can't find them. However,  
> I've
> had to add drive transistors to drive LEDs (digit select on 7  
> segment) on
> 3V systems while I did not on 5V systems. It also makes sense, since
> there's not as much gate voltage on the FETs when the supply  
> voltage is
> not as high. But, I think you're right about it being on the  
> datasheet (I
> can't find it!).
>
> Harold

Exactly, I would of thought its on there because, if its not there,  
I'm not entirely sure how
I'm meant to know what current I can expect from each pin.  I'm  
currently setup to drive
some LEDs directly on a matrix, I may have to reconsider this has you  
had to.

Though I may be better off running at 5v and doing the level  
conversions on i2c and
serial (yes I know its not rs232 until it hits the maxim chip).

Anyway it appears I can do my light loading on the tx channel without  
any interference
in serial communications.

Cheers all.

Ed



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