RS-232 Tx / Rx monitoring LEDs?

Chuck Guzis cclist at
Wed Aug 19 23:04:07 CDT 2015

On 08/19/2015 08:40 PM, dwight wrote:
> I think the main issue is that TTL is usually a weak pullup and a
> hard pulldown. RS 232 levels are equal up and down. Putting it on the
> RS232 lines could even improve signal quality because the signal is
> usually poorly terminated, causing reflections. The recommended
> lengths and Baud rates are intended to account for this. Usually the
> line is lower impedance than the input termination, requiring the
> source to absorb the reflected signal. This is why 422/485 came to
> be. The impedance of the loads better match that of the termination.

My setup with a DM232A doing the level translation lights up the LEDs in 
one of those inline LED line monitors just fine without any apparent 
signal degradation.


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