74F191 Philips, 74F191 Datasheet - Page 5

• Manufacturer Part Number: 74F191
• Description: Up/down binary counter with reset and ripple clock
• Manufacturer: Philips

Philips Semiconductors
APPLICATIONS
The 74F191 simplifies the design of multi-stage counters, as
indicated in Figure 1, each RC output is used as the clock input for
the next higher stage. When the clock source has a limited drive
capability this configuration is particularly advantageous, since the
clock source drives only the first stage. It is only necessary to inhibit
the first stage to prevent counting in all stages, since a High signal
on CE inhibits the RC output pulse as indicated in the Mode Select
Table. The timing skew between state changes in the first and last
stages is represented by the cumulative delay of the clock as it
ripples through the preceding stages. This is a disadvantage of the
configuration in some applications.
Figure 1b shows a method of causing state changes to occur
simultaneously in all stages. The RC output signals propagate in
1995 Jul 17
Up/Down binary counter with reset and ripple clock
DIRECTION CONTROL
DIRECTION CONTROL
DIRECTION CONTROL
ENABLE
CLOCK
b. Synchronous N-Stage Counter with Common Clock Using Ripple/Clock
c. Synchronous N-Stage Counter with Common Clock and Terminal Count
ENABLE
ENABLE
CLOCK
CLOCK
* = Carry Gate
U/D
CE
CP
U/D
CE
CP
U/D
CE
CP
a. N-Stage Counter Using Ripple Clock
TC
RC
RC
*
Figure 1.
U/D
CE
CP
U/D
CE
CP
U/D
CE
CP
5
ripple fashion and all clock inputs are driven in parallel. The Low
state duration of the clock in this configuration must be long enough
to allow the negative-going edge of the RC signal to ripple through
to the last stage before the clock goes High. Since the RC output of
any package goes High shortly after its clock input goes High, there
is no such restriction on the High state duration of the clock.
In Figure 1c, the configuration shown avoids ripple delays and their
associated restrictions. The combined TC signals from all the
preceding stages forms the CE input signal for a given stage. An
enable signal must also be included in each carry gate in order to
inhibit counting. The TC output of a given stage is not affected by its
own CE, therefore, the simple inhibit scheme of Figure 1a and 1b
does not apply.
RC
RC
TC
*
U/D
CE
CP
U/D
CE
CP
U/D
CE
CP
RC
RC
TC
SF00733
Product specification
74F191