74LS191

更新时间： 2024-11-16 22:53:15

品牌	Logo	应用领域
飞兆/仙童 - FAIRCHILD		计数器
页数	文件大小	规格书
6页	75K
描述
Synchronous 4-Bit Up/Down Counter with Mode Control

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74LS191 数据手册

August 1986

Revised February 1999

DM74LS191

Synchronous 4-Bit Up/Down Counter with Mode Control

Two outputs have been made available to perform the cas-

cading function: ripple clock and maximum/minimum count.

General Description

The DM74LS191 circuit is a synchronous, reversible, up/

The latter output produces a high-level output pulse with a

down counter. Synchronous operation is provided by hav-

duration approximately equal to one complete cycle of the

ing all flip-flops clocked simultaneously, so that the outputs

clock when the counter overflows or underflows. The ripple

change simultaneously when so instructed by the steering

clock output produces a low-level output pulse equal in

logic. This mode of operation eliminates the output count-

width to the low-level portion of the clock input when an

ing spikes normally associated with asynchronous (ripple

overflow or underflow condition exists. The counters can be

clock) counters.

easily cascaded by feeding the ripple clock output to the

The outputs of the four master-slave flip-flops are triggered

on a LOW-to-HIGH level transition of the clock input, if the

enable input is LOW. A HIGH at the enable input inhibits

counting. Level changes at either the enable input or the

down/up input should be made only when the clock input is

HIGH. The direction of the count is determined by the level

of the down/up input. When LOW, the counter counts up

and when HIGH, it counts down.

enable input of the succeeding counter if parallel clocking

is used, or to the clock input if parallel enabling is used.

The maximum/minimum count output can be used to

accomplish look-ahead for high-speed operation.

Features

■ Counts binary

■ Single down/up count control line

■ Count enable control input

The counter is fully programmable; that is, the outputs may

be preset to either level by placing a LOW on the load input

and entering the desired data at the data inputs. The output

will change independent of the level of the clock input. This

feature allows the counters to be used as modulo-N divid-

ers by simply modifying the count length with the preset

inputs.

■ Ripple clock output for cascading

■ Asynchronously presettable with load control

■ Parallel outputs

■ Cascadable for n-bit applications

■ Average propagation delay 20 ns

■ Typical clock frequency 25 MHz

The clock, down/up, and load inputs are buffered to lower

the drive requirement; which significantly reduces the num-

ber of clock drivers, etc., required for long parallel words.

■ Typical power dissipation 100 mW

Ordering Code:

Order Number

DM74LS191M

DM74LS191N

Package Number

M16A

Package Description

16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150” Narrow Body

16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300” Wide

N16E

Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.

DS006405.prf

www.fairchildsemi.com

12 3 4 5 6

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与74LS191相关器件

型号	品牌	获取价格	描述	数据表
74LS191B	NXP	获取价格	Binary Counter, LS Series, Synchronous, Positive Edge Triggered, 4-Bit, Bidirectional, TTL
74LS191D	ROCHESTER	获取价格	Decade Counter,
74LS191DCQM	FAIRCHILD	获取价格	Binary Counter, Synchronous, Bidirectional, TTL, CDIP16,
74LS191DCQR	FAIRCHILD	获取价格	Binary Counter, Synchronous, Bidirectional, TTL, CDIP16,
74LS191N	ROCHESTER	获取价格	Decade Counter,
74LS191NA+2	RAYTHEON	获取价格	Binary Counter, Synchronous, Bidirectional, TTL, PDIP16,
74LS192	ONSEMI	获取价格	PRESETTABLE BCD/DECADE UP/DOWN COUNTER PRESETTABLE 4-BIT BINARY UP/DOWN COUNTER
74LS192	HITACHI	获取价格	Synchronous Up/Down Decade Counters(dual clock lines)
74LS192	MOTOROLA	获取价格	PRESETTABLE BCD/DECADE UP/DOWN COUNTER PRESETTABLE 4-BIT BINARY UP/DOWN COUNTER
74LS192B	NXP	获取价格	Decade Counter, LS Series, Synchronous, Positive Edge Triggered, 4-Bit, Bidirectional, TTL

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