© 2000 Fairchild Semiconductor Corporation DS006292 www.fairchildsemi.com
April 1984
Revised March 2000
DM74AS169A Synchronous 4-Bit Binary Up/Down Counter
DM74AS169A
Synchronous 4-Bit Binary Up/Down Counter
General Description
These synchronous presettable counters feature an inter-
nal carry look ahead for cascading in high speed counting
applications. The DM74AS169 is a 4-bit binary up/down
counter. The carry output is decoded to prevent spikes dur-
ing normal mode of counting operation. Synchronous oper-
ation is provided so that outputs change coincident with
each other when so instructed by count enable inputs and
internal gating. This mode of operation eliminates the out-
put counting spikes which are normally associated with
asynchronous (ripple clock) counters. A buffered clock
input triggers the four flip-flops on the rising (positive going)
edge of clock input waveform.
These counters are fully programmable; that is, the outputs
may each be preset either HIGH or LOW. The load input
circuitry allows loading with carry-enable output of cas-
caded 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 approxi-
mately equal to the HIGH portion of the QA output when
counting UP, and approximately equal to the LOW portion
of the QA 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.
The control functions for these counters are fully synchro-
nous. 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
enabled, disabled, loading or counting) will be dictated
solely by the conditions meeting the stable setup and hold
times.
Features
■ Switching Specifications at 50 pF
■ Switching Specifications guaranteed over full tempera-
ture and V
CC
range
■ Advanced oxide-isolated, ion-implanted Schottky TTL
process
■ Functionally and pin-for-pin compatible with Schottky
and low power Schottky TTL counterpart
■ Improved AC performance over Schottky and low power
Schottky counterparts
■ Synchronously programmable
■ Internal look ahead for fast counting
■ Carry output for n-bit cascading
■ Synchronous counting
■ Load control line
■ ESD inputs
Ordering Code:
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Order Number Package Number Package Description
DM74AS169AM M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
DM74AS169AN N16E 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
