8-bitters and multi-whatever

[Ethan Dicks]

On 9/12/07, Roy J. Tellason <rtellason at verizon.net> wrote:
> On Wednesday 12 September 2007 19:45, Ensor wrote:
> > Hi,
> >
> >   > You don't even need "rs232 levels".
> >
> > MIDI is a "current loop" interface isn't it?
>
> Yup!
>
> But my point is that in prototyping some small SBC the rs232 stuff is about
> the only thing on there typically that needs other than logic power (+5V)
> unless there's some analog stuff there on the board that needs it.

And with MAX232 or DS275-type internal-charge-pump line drivers, you
can get away with +5V only, unless, as you say, you need differential
voltages for analog, or perhaps +12V for motors or something.  For -5V
at a few dozen mA, there's the venerable ICL7660 (an 8-pin DIP/SOIC
and two external caps).

For more sophisticated stuff, one can get isolated +/-5V or +/-12V or
+/-15V potted modules, but those aren't typically required for
microprocessor-type designs.  We did have to stick a +5V->-12V
charge-pump module on our Qbus COMBOARD, 20 years ago, because, IIRC,
BA11 chasses provide +/-12V, but the BA23 does not (or was it some
other MicroVAX chassis?)  I still have a pad of them, but no real need
for them since I prototype with MAX232s, not 1488/1489s.

-ethan