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From: "Olin Lathrop" <olin_piclist@embedinc.com>
Sent: Sunday, June 27, 2010 1:45 PM
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Subject: Re: [EE] Slew Rate Limited Clock Buffer?

> Marechiare wrote:
>> Still I am not getting why you need to limit slew rate.
>
> I wrote a fairly lengthy post on this yesterday, so I'm not going to 
> repeat
> it.  Basically, reflections and transmission line effects happen at high
> frequencies.  If the signals dumped onto the line don't contain those
> frequencies, then these effects won't matter.  Slew rate limiting is one
> method of low pass filtering the signal to reduce the frequencies that 
> cause
> the problems.
>
>> PIC32 outputs
>> produce very reasonable slew rate as they are internally limited to
>> couple of tenths mA.
>
> Completely wrong.  Go look at a datasheet.  Someone mentioned here that 
> PIC
> is rated for 18mA source/sink.

IIRC, they are rated up to 25mA.
With output impedance around 26 ohms into say, 20pF, the rise time would be 
around 1.5ns, which is pretty quick.
 


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