Abstract: Apparatus for synchronizing a reference clock signal received from a host system with an A/D converter clock signal generated in a data acquisition pod. The pod includes a decoder responsive to communication received from the host for extracting a host reference signal, and a clock signal source for developing an A/D reference clock signal having a frequency that is different from the frequency of the host reference signal. A pulse modifying digital phase-locked loop (PLL) is responsive to the A/D reference clock signal and the host reference signal for developing an A/D clock signal for an A/D converter in which one of its clock periods is periodically modified, thereby locking the rate at which the A/D converter develops samples to the rate at which the host system requests samples.