Abstract: A data rate control device interfacing between a computer and a communication line facilitates reading out of data from the computer at a fast rate and then transmitting that data at a slow rate on the communication line with allowance being made between data transmissions for reflections and echoes on the line to die down. The control device includes a clock generator, control logic and a clock transmitter for sending out Fast Clocks and causing the serial reading in of data to a shift register of the control device. Once the presence of one character of data is detected in the register by the control logic, the Fast Clocks are terminated and Slow Clocks are sent to the register for serial reading out of the data character to a loop transmitter of the control device for transmission of the data character on the communication line.