[time-nuts] More on paralleling output gates

[Poul-Henning Kamp]

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

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