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A complete Arduino library for the MAX3100 serial UART/USART chip can be downloaded below. There have been many requests for an Arduino library for the MAX3100 external serial USART (UART) chip from Maxim Integrated. As an example of the minor changes needed to use the MAX3100's serial port instead of (or in addition to) the built in serial port, here is some sample code (note the lower case 's' is the only change needed to use the new serial port).

// Arduino built-in Serial library
Serial.print("Example serial output ");
if (Serial.available()) Serial.write(;

// MAX3100Serial library
#include <MAX3100Serial.h>
MAX3100Serial serial = MAX3100Serial(1843, 10);  // Initialise MAX3100 instance with 1.8432 MHz crystal and chip select pin 10.
serial.print("Example serial output ");
if (serial.available()) serial.write(;

You can find example code included demonstrating how to use the MAX3100 external interrupts with the library in order to improve power consumption and code response time.