AVR-Chat

On Thu, Dec 15, 2005 at 10:34:00AM -0600, Thomas Keller wrote:
> John Samperi wrote:
> 
> > At 05:52 AM 15/12/2005, you wrote:
> > >0/+3 happens to work on classic 1488/1489 buffers, "but its not right."
> > >
> > >Super serious workstations used to rigidly ahere to +-10 volts.
> >
> >
> > + - 25V being the 'right' voltage :-)
> 
>   Uhm...IIRC correctly, the RS-232C specification reads that the signal 
> voltages are to be +/- 12.5 VDC (25 v total across the two).

There are a lot of places in the net with a lot of conflicting EIA-232
information. Most likely due to the $100 fee for downloading the real
document. Maybe why there are so many bad implementations. +-15 and +-25
volts are the most common max voltages quoted.

The MC1488 driver is rated for up to +-15 volt supply. The MC1489
receiver is rated for +-30 so that goofballs can wire a -+15V source to
ground and a +-15V source to an input and not hurt the part.

http://www.onsemi.com/pub/Collateral/MC1488-D.PDF
http://www.onsemi.com/pub/Collateral/MC1489-D.PDF

In practice driving the MC1488 with +-12V resulted in +-10V outputs.

-- 
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.