[time-nuts] More on paralleling output gates

[John Ackermann N8UR]

Poul-Henning Kamp said the following on 04/09/2006 04:07 PM:
> In message <443967F6.5000709 at febo.com>, John Ackermann N8UR writes:
> 
> 
>>For what it's worth, the risetime of the MAX232 output is about 2.5us,
>>in a very smooth ramp -- it's spec'd at 4 v/us.  I have heard that the
>>risetime is deliberately slow to match the RS-232 spec; I don't know
>>whether that's true.  The later version MAX232A is spec'd at 12 v/us;
>>still not all that speedy.
> 
> 
> It's mainly an EMI issue, if the flanks are too steep, kit fails the
> EC mark test because they're too noisy.
> 
> Since RS-232 is usually limited to around 110kHz max, there is no need
> 4uS is a sufficient flank.
> 
> Poul-Henning
> 

That makes a lot of sense.

John