The 251 is a low cost, single-output, field programmable clock synthesizer. The 251 can generate an output frequency from 314 kHz to 200 MHz and may employ Spread Spectrum techniques to reduce system electro-magnetic interference (EMI). Using IDT's VersaClock™ software to configure the PLL and output, the 251 contains a One-Time Programmable (OTP) ROM to allow field programmability. Programming features include 4 selectable configuration registers. The device employs Phase-Locked Loop (PLL) techniques to run from a standard fundamental mode, inexpensive crystal, or clock. It can replace multiple crystals and oscillators, saving board space and cost. The device also has a power-down feature that tri-states the clock outputs and turns off the PLLs when the PDTS pin is taken low. The 251 is also available in factory programmed custom versions for high-volume applications.