Mark Willis <mwillis@NWLINK.COM> wrote:
>   The 1488 and 1489 "always" exist on any standard serial port (And on
> the better ones, they're socketed so if you should burn them out, you
> can replace them, IMHO at least.)

Often instead of a 1488 and 1489 you'll see a MAX232 or the like, which
integrates receivers, transmitters, and charge pumps.  In PCs the variants
without the charge pumps are often used, since +/-12V are available.
However, many PC power supplys are so wimpy on -12V that good multiport
serial boards use the charge pumps anyhow.

> Some LSI circuits may include them
> internal (on the FGPA etc.), but not always.

I've never heard of such a thing.  Can you cite a reference?

What I've always thought would be useful would be a small chip combining
a 5V linear regulator, undervoltage detect for reset, and a MAX232 (or
even 1/2 of a MAX232, only a single channel each of tx and rx).

In PIC circuits for non-commercial use, I often just use resistors to
interface the PIC to a serial port.  EIA-232 signals are active at negative
voltages, which is normally taken care of by the inverting nature of the
buffer chips, but the PIC can do that in software.  Of course, this doesn't
meet EIA-232 specifications, but it works well enough for casual use with
short cables.

My full-duplex software UART code has conditional assembly directives to
include the necessary inversion.

Eric

http://www.brouhaha.com/~eric/pic/
http://www.brouhaha.com/~eric/scenix/