piclist 1995\12\08\082412a >
Thread: Direct RS-232 Connect
face BY : Newfound Electronics email (remove spam text)

>Hi Folks,

>I presume that it would work because of the low currents involved and the
>fact that RS-232 "0" can be represented by 5V.  Does this mean that a 1 is
>anything less than 3V (which is what i believe the EIA Spec says).

>Myke Predko

The very simple, answer is "YES." This is because any non valid input
voltage is defined as a logic 1 on the output.Don't become confused, this is
the essential point. BUT, as Mike Fahrion pointed out,  there are a some
cases the negative swing is required. Something to keep in mind if it
doesn't work on your friends computer.

RS232 input to a pic can be through a single resistor BUT a diode to Vdd is
required on at least one input, RA4 and possibly others with the 28/40-pin
16Cxx devices.

Of course, this sort of interface belongs to the M2L (Mickey-Mouse logic)
family and design "snobs" would never dream of using it. For many non
critical applications it's ok. Keep in mind that it has poor noise immunity
and may not comply with the slew rate limits of RS232.


See also: www.piclist.com/techref/io/serials.htm?key=rs%2D232
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