What this SPI/UART controller brings to a serial port
The MAX3100EEE+T from Maxim Integrated is a SPI/UART controller that handles both RS232 and RS485 protocols from a single chip. It talks to a host microcontroller over SPI and presents a full UART on the other side — no extra level translators needed if your system runs on a 2.7V to 5.5V rail. The 150 µA supply current means you can leave it powered on a battery-backed serial port without draining the pack overnight.