At 11:43 AM 6/6/97 -0600, Gus Calabrese wrote:
>If you have plus and minus 5v you can do the following:
>
>Put the TTL level signal through a 10K resitor to drive the base of a
>2N3906, emitter connected to -5v through a 1K resistor..  Collector is
>connected to 5v.  TTL high will result in an output at the emitter of
>the 3906 that will be -5v.  TTL low will result in +5v at the emiiter of
>the 3906.
>--
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>WFT Electronics    wft@frii.com   http://www.frii.com/~wft
>Gus Calabrese      303 321-1119......voicemail
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TTL to RS232:  There is a VERY simple way.  It seems too simple to believe,
but if you do not have a serial module and/or you want the minimal hardware
configuration, it is worth a try.  I READ that this will work, but, again,
I have not personally tried it.

Dedicate two I/O pins as your TX and GND lines.  When you want to transmit
an RS232-converted "1", just raise the GND line HIGH and the bring the TX
low.  This will appear to the PC as -5V.  For a logic "0", TX goes HIGH and
GND goes low.  Although it probably doesn't matter, I would do a port write
( or play a trick with tristating) to ensure that both pin levels changed
simultaneously.

Since the RS-232C standard allows for plus/minus 3V poles, this will work.

Comments?

Andrew DeWeerd
Engineer