SN74LS161AN | Texas Instruments

Synchronous 4-Bit Binary Counter, SN74LS161AN, Texas Instruments

This synchronous, presettable counter features an internal carry look-ahead for application in high-speed counting designs. The SN74LS161AN is a 4-bit binary counter. 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 input and internal gating. This mode of operation eliminates the output counting spikes that are normally associated with asynchronous (ripple clock) counters; however, a counting spike may occur on the (RCO) ripple carry output. A buffered clock input triggers the four flip-flops on the rising edge of the clock input waveform.

This counter is fully programmable; that is, the output may be preset to either level. As presetting is synchronous, setting up a low level at the load input disables the counter and causes the output to agree with the setup data after the next clock pulse regardless of the level of the enable input. The clear function for the SN74LS161AN is asynchronous, and a low level at the clear input sets all four flip-flop outputs low regardless of the levels of clock, load, or enable inputs. This synchronous clear allows the count length to be modified easily as decoding the maximum count desired can be accomplished with one external NAND gate. The gate output is connected to the clear input to synchronously clear the counter to 0000 (LLLL).

Features

• Internal Look-Ahead for Fast Counting
• Carry Output for n-Bit Cascading
• Synchronous Counting
• Synchronously Programmable
• Load Control Line
• Diode-Clamped Inputs