Features: *Switching specifications at 50 pF
*Switching specifications guaranteed over full tempera-ture and VCC 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
*ESD inputs
SpecificationsSupply Voltage 7V
Input Voltage 7V
Operating Free Air Temperature Range 0 to +70
Storage Temperature Range -65 to +150
Typical JA
N Package 78.1/W
M Package 106.8/WDescription These DM74ALS169B synchronous presettable counters feature an inter-nal carry look ahead for cascading in high speed counting applications. The DM74ALS169B is a four-bit binary up/down counter. The carry output is decoded to prevent spikes during normal mode of counting operation. Synchro-nous operation is provided so that outputs change coinci-dent with each other when so instructed by count enable inputs and internal gating. This mode of operation elimi-nates the output counting spikes which are normally asso-ciated 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 DM74ALS169B 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 DM74ALS169B 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 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 DM74ALS169B 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.
DM74ALS169B Data Sheet
