I knew that the "patents" would be coming out of the woodwork. There is no reliable alternative to making RS232 swing +- 10V. While it is, indeed, possible to achieve that with discrete components that is not an undertaking for the faint of heart. The last reliable discrete RS232 implementation I saw required dual power supply +- 10V. Of course you can use a MAX232 to generate those voltages and implement the rest in discretes. The "solutions" wit 0-+5 swing will fail in some cases and do you really want to spend your time doubting whether ir is the "patent solution" or you code that fail.

Remember the discussions "my patent RS232 that I know works does not work with my new PC" and "my patent RS232 that I know works is dropping bits"

Erik