There's NO WAY you can build an RS-232-compliant interface with resistors alone and no negative supply. If you know a trick that "works" then you should spell it out, particularly if you know it doesn't work. Nobody, and I mean NOBODY, believes that you can interface at RS232 levels without a negative supply. It just happens that the MAX232 generates its own, rather noisy, negative and positive supplies for the interface.

You need a negative supply, as the levels are minally 3 volts to either side of signal common. There are lots of circuits other than MAX232 types that produce those levels just fine, given the proper supply. Lots of applications include both positive and negative supplies. Maxim even makes a component (DS275) that steals the negative supply from the serial port signals to the terminal/host.

RE