Abstract: In a data transmission system, in which asynchronous-to-synchronous data conversion at the transmitter end of a data link at times removes stop bits from, and at other times adds stop bits, to a character, a receive buffer at the receive end of the data link which converts the synchronous data to asynchronous data. The receive buffer investigates the end of each character for missing stop bits and reinserts a stop bit where it finds a lack of one, and adds other stop bits to speed up the data rate from the nominal synchronous data bit transmission rate to the nominal asynchronous data bit output rate. The inserted stop bits are of a constant bit width which is the same as the character identification bit width, and the entire asynchronous data output stream has a constant bit rate.