First of all, you need to practice reading.

You've failed to read the datasheets correctly. I conclude this from the evidence, i.e. you keep going on about receiver noise margins which in no way are associated with the negative supply. While I admit a negative supply COULD, possibly, perhaps, improve the noise margin, there's no indication anywhere that any RS232 receiver uses it, so I challenge you to support the notion that the receiver section of a transceiver that doesn't use the negative supply benefits from it. Now, if you can show that the MAX-series uses the negative supply to enhance noise margin, then I'll agree. Until then, and I submit it will be a long time, I'll continue to believe and assert that the negative supply, be it -3 or -15, won't contribute anything in these circuits.

Secondly, you need to practice spelling. I've pointed out before what the correct spelling of a few words you frequently misspell is. These aren't typo's, as you constantly mistype them the same way.

More importantly, however, you need to practice stating your position correctly. Start by showing where any datasheet for any RS232 receiver offers greater noise margin by using a negative supply. You keep babbling about noise margins but don't indicate what or where they are, let alone what role the negative supply has in the process.

Any idiot will agree that six volts are greater than three, but that fact has little to do with noise margins on RS232 communications.

RE