The Serial I/O (SIO) port of Oki’s Advantage Microcontrollers is a two pin asynchronous interface, similar to a UART with the exception that it only has the Tx and Rx pins. The SIO does not have the modem signal pins typically found in full function UARTs. Also, it does not have built in buffers for Tx and Rx data. Typically it can be used for RS232 serial communication up to 115 Kbaud.