I couldn't see how the conversation had wandered to where it was. If one has no negative supply, one has to "make do" and the MAX part, or equivalent, is the most popular way. If one has a negative supply, however, it makes little if any sense at all to use anything other than the old-standard part, even if one has a box full of MAX parts. There are probably reasons, but those seldom come up here, e.g. "It's impossible to fit a route for even one more supply or signal to these devices." The 75155 works just fine with a bipolar 5 volt supply, and that seems to be about all the MAX3232 can produce... well maybe a bit closer to (+/-) 6, but only if the V+ input is adequate. Those things require passives, and they take up space too. In a portable device running from 3 volts or so, I can see using a charge pump if one can tolerate the noise, but since the device is portable, one doesn't need it, does one?

When you attach to a "base station" you can feed the bipolar supply to the portable device if you need to. There's no need for this sort of thing on a mains-driven device, since, if you don't have the biplar supply in the base unit, you can use a '423 or '485 interface that uses only the +5 or lower.

Maybe it's time, too, for folks to be reading the venerable RS232 standard again, as some notes indicate they fail to remember the limitations on cable length, baud rate, etc.

RE