A method of operating an implantable medical device (IMD) includes demodulating a data signal incoming to the IMD, serially storing demodulated data received in the data signal in a first serial buffer register, transferring the received demodulated data to a parallel buffer register from the first serial buffer register, wherein the parallel buffer register operates according to a clock signal having a lower frequency than a clock signal used to operate a serial buffer register, switching the serial storing of demodulated data to a second serial buffer register during the transferring of the received demodulated data to the parallel buffer register, and alternating the serial storing of the received data between the first and second serial buffer registers.