These synchronous, presettable counters feature an internal carry look-ahead for application in high-speed counting designs. The LS161A and LS163A are 4-bit binary counters. The carry output is decoded by means of a NOR gate, thus preventing spikes during the normal counting mode of operation. Synchronous operation is provided by having all flipflops clocked simultaneously so that the outputs change coincident with each other when so instructed by the countenable inputs and internal gating. This mode of operation eliminates the output counting spikes which are normally associated with asynchronous (ripple clock) counters. A buffered clock input triggers the four flip-flops on the rising (positive-going) edge of the clock input waveform.
■ Synchronously programmable
■ Internal look-ahead for fast counting
■ Carry output for n-bit cascading
■ Synchronous counting
■ Load control line
■ Diode-clamped inputs
■ Typical propagation time, clock to Q output 14 ns
■ Typical clock frequency 32 MHz
■ Typical power dissipation 93 mW
■ Alternate Military/Aerospace device (54LS161, 54LS163) is available. Contact a National Semiconductor Sales Office/Distributor for specificaitons.