IDT's ICS841S10x PCI Express Clock Synthesizers are a PLL-based clock synthesizer specifically designed for PCI_Express™ Clock applications. These devices generates a 100MHz differential HCSL clock from a input reference of 25MHz. The input reference may be derived from an external source or by the addition of a 25MHz crystal to the on-chip crystal oscillator. An external reference is applied to the XTAL_IN pin with the XTAL_OUT pin left floating. They offer spread spectrum clock output for reduced EMI applications. An I2C bus interface is used to enable or disable spread spectrum operation as well as select either a down spread value of -0.35% or -0.5%.