The 74HC6323A; 74HCT6323A is an oscillator designed for quartz crystal combined with a programmable 3-state counter, a 3-state output buffer and an overriding asynchronous master reset (MR). With the two select inputs S1 and S2 the counter can be switched in the divide-by-1, 2, 4 or 8 mode. If left floating the clock is divided by 8. The oscillator is designed to operate either in the fundamental or third overtone mode depending on the crystal and external components applied. On-chip capacitors minimize external component count for third overtone crystal applications. The oscillator may be replaced by an external clock signal at input X1. In this event the other oscillator pin (X2) must be floating. The counter advances on the negative-going transition of X1. A LOW level on MR resets the counter, stops the oscillator and sets the output buffer in the 3-state condition. MR can be left floating since an internal pull-up resistor will make the MR inactive.

The X1 input has CMOS input switching levels and may be driven by a TTL output using a pull-up resistor connected to V_CC. Inputs include clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in excess of V_CC.