1. General description
The 74LVC169 is a synchronous presettable 4-bit binary counter which features an
internal look-ahead carry circuitry for cascading in high-speed counting applications.
Synchronous operation is provided by having all flip-flops clocked simultaneously so that
the outputs (pins Q0 to Q3) change simultaneously with each other when so instructed by
the count-enable (pins CEP
and CET) inputs and internal gating. This mode of operation
eliminates the output counting spikes that are normally associated with asynchronous
(ripple clock) counters. A buffered clock (pin CP) input triggers the four flip-flops on the
LOW-to-HIGH transition of the clock.
The counter is fully programmable; that is, the outputs may be preset to any number
between 0 and its maximum count. Presetting is synchronous with the clock and takes
place regardless of the levels of the count enable inputs. A LOW level on the parallel
enable (pin PE
) input disables the counter and causes the data at the Dn input to be
loaded into the counter on the next LOW-to-HIGH transition of the clock. The direction of
the counting is controlled by the up/down (pin U/D
) input. When pin U/D is HIGH, the
counter counts up, when LOW, it counts down.
The look-ahead carry circuitry is provided for cascading counters for n-bit synchronous
applications without additional gating. Instrumental in accomplishing this function are two
count-enable (pins CEP
and CET) inputs and a terminal count (pin TC) output. Both
count-enable (pins CEP
and CET) inputs must be LOW to count. Input pin CET is fed
forward to enable the terminal count (pin TC
) output. Pin TC thus enabled will produce a
LOW-level output pulse with a duration approximately equal to a HIGH level portion of
pin Q0 output. The LOW level pin TC
pulse is used to enable successive cascaded
stages.
The 74LVC169 uses edge triggered J-K type flip-flops and has no constraints on changing
the control of data input signals in either state of the clock. The only requirement is that
the various inputs attain the desired state at least a set-up time before the next
LOW-to-HIGH transition of the clock and remain valid for the recommended hold time
thereafter.
The parallel load operation takes precedence over the other operations, as indicated in
the mode select table. When pin PE
is LOW, the data on the input pins D0 to D3 enters
the flip-flops on the next LOW-to-HIGH transition of the clock.
74LVC169
Presettable synchronous 4-bit up/down binary counter
Rev. 6 — 29 November 2012 Product data sheet
