DM74LS169A Synchronous 4-Bit Up/Down Binary Counter
April 1998
DM74LS169A
Synchronous 4-Bit Up/Down Binary Counter
General Description
This synchronous presettable counter features an internal
carry look-ahead for cascading in high-speed counting appli-
cations. Synchronous operation is provided by having all
flip-flops clocked simultaneously, so that the outputs all
change at the same time when so instructed by the
count-enable inputs and internal gating. This mode of opera-
tion helps eliminate the output counting spikes that are nor-
mally associated with asynchronous (ripple clock) counters.
A buffered clock input triggers the four master-slave flip-flops
on the rising edge of the clock waveform.
This counter is fully programmable; that is, the outputs may
each be preset either high or low. The load input circuitry al-
lows loading with the carry-enable output of cascaded
counters. As loading is synchronous, setting up a low level at
the load input disables the counter and causes the outputs to
agree with the data inputs after the next clock pulse.
The carry look-ahead circuitry permits cascading counters
for n-bit synchronous applications without additional gating.
Both count-enable inputs (P and T) must be low to count.
The direction of the count is determined by the level of the
up/down input. When the input is high, the counter counts
up; when low, it counts down. Input T is fed forward to enable
the carry outputs. The carry output thus enabled will produce
a low-level output pulse with a duration approximately equal
to the high portion of the Q
A
output when counting up, and
approximately equal to the low portion of the Q
A
output when
counting down. This low-level overflow carry pulse can be
used to enable successively cascaded stages. Transitions at
the enable P or T inputs are allowed regardless of the level
of the clock input. All inputs are diode clamped to minimize
transmission-line effects, thereby simplifying system design.
This counter features a fully independent clock circuit.
Changes at control inputs (enable P, enable T, load, up/
down), which modify the operating mode, have no effect until
clocking occurs. The function of the counter (whether en-
abled, disabled, loading, or counting) will be dictated solely
by the conditions meeting the stable setup and hold times.
Features
n
Fully synchronous operation for counting and
programming.
n
Internal look-ahead for fast counting.
n
Carry output for n-bit cascading.
n
Fully independent clock circuit
Connection Diagram
Dual-In-Line Package
DS006401-1
Order Number 54LS169DMQB, 54LS169FMQB, 54LS169LMQB,
DM54LS169AJ, DM54LS169AW, DM74LS169AM or DM74LS169AN
See Package Number E20A, J16A, M16A, N16E or W16A
漏 1998 Fairchild Semiconductor Corporation
DS006401
www.fairchildsemi.com
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