Back in the days when air was clean and sex was dirty, and dinosaurs roamed the earth, we didn't have Max232, or other devices of that ilk. Instead, it was common practice to use an old (DTL?) device, the MC1489 as an RS-232-compatible receiver. If you look at any old PC serial I/O adapter, you'll find 'em, and won't see a single MAX-anything.

Receiving RS-232 signals doesn't require a negative supply, as I've already attempted to explain in a couple of ways.

Transmitting is a different issue, however.

Nonetheless, it's conceivable that one might want to recieve without ever transmitting, e.g. in the case of a simple control that receives commands on one channel and, perhaps, doesn't have to respond in any way other than performing a specific procedure, monitored elsewhere in order to close the loop.

RE