Rev.2.00, Feb.18.2005, page 1 of 10

HD74LS191

Synchronous Up / Down 4-bit Binary Counter (single clock line)

REJ03D0453–0200

Rev.2.00

Feb.18.2005

Synchronous operation is provided by having all flip-flops clocked simultaneously so that the steering logic. This mode

of operation eliminates the output counting spikes normally associated with asynchronous (ripple clock) counters. 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 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. Level changes at the down / up input should be made only when the clock

input is high. This 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 to agree with the data inputs

independently of the level of the clock input. This feature allows the counters to be used as modulo-N dividers by

simply modifying the count length with the preset inputs. The clock, down / up, and load inputs are buffered to lower

the drive requirement which significantly reduces the number of clock drivers, etc., required for long parallel words.

Two outputs have been made available to perform the cascading function; ripple clock and made available to perform

the cascading function; ripple clock and maximum / minimum count. The latter output produces a high-level output

pulse with a duration approximately equal to one complete cycles to the clock when the counter overflows or

underflows. The ripple clock output produces a low-level output pulse equal in width to the low-level portion of the

clock input when an overflow or underflow condition exists.

The counters can be easily cascaded by feeding the ripple clock output to the 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

• Ordering Information

Part Name

Package Type

Package Code

(Previous Code)

Package

Abbreviation

Taping Abbreviation

(Quantity)

HD74LS191P

DILP-16 pin

PRDP0016AE-B

(DP-16FV)

P

—

HD74LS191FPEL

SOP-16 pin (JEITA)

PRSP0016DH-B

(FP-16DAV)

FP

EL (2,000 pcs/reel)

Note:

Please consult the sales office for the above package availability.