74LS161中文资料仙童半导体数据手册PDF规格书

General Description

These synchronous, presettable counters feature an internal carry look-ahead for application in high-speed counting designs. The DM74LS161A and DM74LS163A 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 flip-flops clocked simultaneously so that the outputs change coincident with each other when so instructed by the count-enable 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.

特性 Features

■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