The 74LVC163 is a synchronous presettable binary counter which features an internal look-ahead carry and can be used for high-speed counting. Synchronous operation is provided by having all flip-flops clocked simultaneously on the positive-going edge of the clock (pin CP). The outputs (pins Q0 to Q3) of the counters may be preset to a HIGH-level or LOW-level. A LOW-level at the parallel enable input (pin PE) disables the counting action and causes the data at the data inputs (pins D0 to D3) to be loaded into the counter on the positive-going edge of the clock (provided that the set-up and hold time requirements for PE are met). Preset takes place regardless of the levels at count enable inputs (pin CEP and CET). A LOW-level at the master reset input (pin MR) sets all four outputs of the flip-flops (pins Q0 to Q3) to LOW-level after the next positive-going transition on the clock input (pin CP) (provided that the set-up and hold time requirements for PE are met). This action occurs regardless of the levels at input pins PE, CET and CEP. This synchronous reset feature enables the designer to modify the maximum count with only one external NAND gate.
The look-ahead carry simplifies serial cascading of the counters. Both count enable inputs (pin CEP and CET) must be HIGH in count. The CET input is fed forward to enable the terminal count output (pin TC). The TC output thus enabled will produce a HIGH output pulse of a duration approximately equal to a HIGH-level output of Q0. This pulse can be used to enable the next cascaded stage.
The maximum clock frequency for the cascaded counters is determined by tPHL (propagation delay CP to TC) and tsu (set-up time CEP to CP) according to the formula: fmax=1/(tPHL(max)+tsu)