Most of the time, TTL levels will work just fine....

...which means that sometimes, TTL levels will NOT work.

http://www.piclist.com/techref/io/serial/RCL1.htm Converts TTL to RS232 when
needed

(shameless plug)

---
James.
 
 

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Tony Smith
> Sent: 2007 Jan 12, Fri 19:26
> To: 'Microcontroller discussion list - Public.'
> Subject: RE: [EE] Very odd problem with RS232...
> 
> > 
> > I could be out of date with this but RS-232 specs I have 
> used in the 
> > past go from a + level to a -level. 0 volts is an invalid condition.
> > I would put a scope there to see.
> > 
> > John Ferrell    W8CCW
> 
> 
> +3 to -3 volts is invalid.  -15 to -3 is logic 1, +15 to +3 
> is logic 0.
> 
> Tony
> 
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