CD54HC190, CD74HC190

CD54HC191, CD74HC191, CD54HCT191, CD74HCT191

SYNCHRONOUS UP/DOWN COUNTERS WITH DOWN/UP MODE CONTROL

SCHS275E − MARCH 2002 − REVISED OCTOBER 2003

2

POST OFFICE BOX 655303

description/ordering information (continued)

When an overflow or underflow of the counter occurs, the MAX/MIN output, which is low during counting, goes

high and remains high for one clock cycle. This output can be used for look-ahead carry in high-speed cascading

(see Figure 1). The MAX/MIN output also initiates the ripple clock (RCO) output, which normally is high, goes

low, and remains low for the low-level portion of the clock pulse. These counters can be cascaded using RCO

(see Figure 2).

If a decade counter is preset to an illegal state or assumes an illegal state when power is applied, it returns to

the normal sequence in one or two counts, as shown in the state diagrams (see Figure 3).

FUNCTION TABLE

INPUTS

FUNCTION

LOAD

CTEN

D/U

CLK

FUNCTION

H

L

L

Count up

H

L

H

Count down

L

X

X

X

Asynchronous preset

H

H

X

X

No change

D/U or CTEN should be changed only when clock is high.

X = Don’t care

Low-to-high clock transition