SN74F161A Datasheet, PDF (1/9 Pages) Texas Instruments – SYNCHRONOUS 4-BIT BINARY COUNTER

SN74F161A
SYNCHRONOUS 4-BIT BINARY COUNTER
SDFS056A – D2932, MARCH 1987 – REVISED OCTOBER 1993
• Internal Look-Ahead Circuitry for Fast
Counting
D OR N PACKAGE
(TOP VIEW)
• Carry Output for N-Bit Cascading
• Fully Synchronous Operation for Counting
• Package Options Include Plastic
Small-Outline Packages and Standard
Plastic 300-mil DIPs
description
CLR 1
CLK 2
A3
B4
C5
D6
ENP 7
16 V_CC
15 RCO
14 Q_A
13 Q_B
12 Q_C
11 Q_D
10 ENT
This synchronous, presettable, 4-bit binary
GND 8
9 LOAD
counter features an internal carry look-ahead
circuitry for application in high-speed counting
designs. 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 (ENP, ENT) inputs and internal gating. This mode of operation eliminates the
output counting spikes that are normally associated with asynchronous (ripple-clock) counters; however,
counting spikes may occur on the ripple-carry (RCO) output. A buffered clock (CLK) input triggers the four
flip-flops on the rising (positive-going) edge of the clock input waveform.
This counter is fully programmable; that is, it may be preset to any number between 0 and 15. As presetting is
synchronous, setting up a low level at the load (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 clear function for the SN74F161A is asynchronous and a low level at the clear (CLR) input sets all four of
the flip-flop outputs low regardless of the levels of the clock, load, or enable inputs.
The carry look-ahead circuitry provides for cascading counters for n-bit synchronous applications without
additional gating. Instrumental in accomplishing this function are two count-enable (ENP, ENT) inputs and a
ripple-carry (RCO) output. Both ENP and ENT must be high to count, and ENT if fed forward to enable RCO.
RCO thus enabled will produce a high-level pulse while the count is 15 (HHHH). The high-level overflow
ripple-carry pulse can be used to enable successive cascaded stages. Transitions at ENP or ENT are allowed
regardless of the level of the clock input.
The SN74F161A features a fully independent clock circuit. Changes at control inputs (ENP, ENT, or LOAD) that
will modify the operating mode have no effect on the contents of the counter until clocking occurs. The function
of the counter (whether enabled, disabled, loading, or counting) will be dictated solely by the conditions meeting
the setup and hold times.
The SN74F161A is characterized for operation from 0°C to 70°C.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
Copyright © 1993, Texas Instruments Incorporated
2–1