SL74LS161

System Logic

Semiconductor

SLS

Synchronous 4 Bit Counters; Binary,

Direct Reset

This synchronous, presettable counter features an internal carry

look-ahead

for

application

in

high-speed

counting

designs.

Synchronous operation is provided by having all flip-flops clocked

simultaneously so that the outputs change conicident with each other

when so instructed by the count-enable inputs and internal gating.

This mode of operation eliminates the output counting spikes that

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 wave form.

This counter is fully programmable; that is the outputs 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 outputs to

agree with the setup data after the next clock pulse regardless of the

levels of the enable inputs.

The carry look-ahead circuitry provides for cascading counters for

n-bit synchronous applications without additional gating. Instrumental

in accomplishiing this function are two counter-enable inputs and a

ripple carry output. Both countenable inputs (ENABLE P and

ENABLE T) must be high to count, and ENABLE T is fed forward to

enable the ripple carry output. The ripple carry output thus enabled

will produce a high-level output pulse with a duration approximately

overflow ripple carry pulse can be enable successive cascaded

stages. Transitions at the ENPor ENT are allowed regardless of the

level of the clock input.

• Internal Look-Ahead for Fast Counting

• Carry Output for n-Bit Cascading

• Synchronous Counting

• Synchronously Programmable

• Load Control Line

• Diode-Clamped Inputs

ORDERING INFORMATION

SL74LS161N Plastic

SL74LS161D SOIC

° to 70° C for all

packages

PIN ASSIGNMENT

LOGIC DIAGRAM

PIN 8 = GND