oddball televideo problem

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Jan 16 17:29:15 2004

>
> > [Actually, I'll admit to having fed the output of an HCT04 (or
> similar)
> > into a serial port once. My excuse it that it waas a one-off test
> board,
> > and I had the schematics of the serial card it was driving (which
> showed
> > a 1489 reciever).
>
> I once used a dual opamp in an 8-pin DIL to do that. One half was the
> receiver, one the driver. I knew that what I was driving wouldn't
> overload the opamp's output, and it kept the chip count down (it was a
> small microcomputer based on a Z8, on a board about 3" square).
>

I've seen op-amps used as RS232 drivers in commercial devices -- I think
some of the early HP RS232 ports (for things like the 9830) used them.
Probably didn't meet the spec though...

One trick I don't like, but it's very common, is to feed the RS232 input
into an HCT or HC gate with a 10k resistor in series, using the
protection diodes of the CMOS input to clamp the signal. HP have done
this as well...

-tony
Received on Fri Jan 16 2004 - 17:29:15 GMT