A single-wire communication bus couples a transmitting device to a UART in a receiving device. Flow control circuitry in the UART fills a transmit memory buffer with remote data. The UART supplies a remote start bit onto the single-wire bus for each byte of remote data written into the transmit memory buffer. After detecting a remote start bit on the single-wire bus, the transmitting device supplies initial data bits and a stop bit, which together form an RS232 character. Data flow is controlled when the UART supplies a subsequent remote start bit only after data has been read out of the UART freeing up bytes in a receive memory buffer. After the transmitting device detects the subsequent remote start bit, the transmitting device supplies subsequent data bits onto the single-wire bus. In another embodiment, flow control circuitry functionality is performed by flow control code in the receiving device operating system.