Abstract: A data exchange circuit to change modified frequency modulation (MFM) signals read from a magnetic memory media and converted into data pulse signals to non-return-to-zero signals. The circuit comprises an input flip-flop which receives MFM data pulse signals from a pulse forming circuit. Pre outputs of the input flip-flop is received by a phase locked loop and the other output of the input flip-flop is received by a delay circuit to vary the pulse width of the MFM pulse signal. Instruction signals are provided to the delay circuit to define data reading margins, and to accommodate variations in data widths or data shifts when no particular margin is determined. The phase locked loop synchronizes it's output when the output of the MFM data pulse signal in order to provide clock signals for non-return-to-zero data. The outputs of the phase locked loop and the delay circuit are converted to respective flip-flops in order to generate the non-return-to-zero signals.