Features: ·Internal Look-Ahead Circuitry for Fast Counting
·Carry Output for n-Bit Cascading
·Synchronous Counting
·Synchronously Programmable
·Package Options Include Plastic Small-Outline (D) and Shrink Small-Outline (DB) Packages, Ceramic Chip Carriers (FK), Standard Plastic (N) and Ceramic (J) DIPsPinout
SpecificationsSupply voltage range, VCC . . . . . . . . . . . . . . .-0.5 V to 7V
Input voltage range, VI . . . . . . . . . . . . . .. . . -0.5 V to 7V
Package thermal impedance, JA
(see Note 1):D package . . . . . . . . . . . . . . . . . . .73/W
DB package . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82/W
N package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67/W
Storage temperature range, Tstg . . . . . . . -60 to 150
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratis only, and functional operation of the device at these or any other conditions beyond those indicated under !recommended operating conditons' is no implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
NOTE 1:The package thermal impedance is calculated in accordance with JESD 51.
DescriptionThese !flALS161B and 'AS161 synchronous, presettable, 4-bit decade and binary counters feature an internal carry look-ahead circuitry for application in high-speed counting designs. The SN54ALS162B is a 4-bit decade counter. The !flALS161B and 'AS161 devices are 4-bit bina counters. Synchronous operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincidentally with each other when instructed by the count-enable (ENP, ENT) inputs and internal gating. This mode of operation eliminates the output counting spikes normally associated with asynchronous (ripple-clock) counters. A buffered clock (CLK) input triggers the four flip-flops on the rising (positive-going) edge of the clock input waveform.
These counters are fully programmable; they can be preset to any number between 0 and 9 or 15. Because presetting is synchronous, setting up a low level at the load (LOAD) input disables the counter and causes the outputs to agree with the setup data after the next clock pulse, regardless of the levels of the enable inputs.
The clear function for the !flALS161B and 'AS161 devices is asynchronous. A low level at the clear (CLR) input , or enable inputs. The clear sets all four of the flip-flop outputs low, regardless of the levels of the CLK, LOAD function for the SN54ALS162B, !flALS163B, and !flAS163 devices is synchronous, and a low level at CLR sets all four of the flip-flop outputs low after the next clock pulse, regardless of the levels of the enable inputs. This synchronous clear allows the count length to be modified easily by decoding the Q outputs for the maximum count desired. The active-low output of the gate used for decoding is connected to CLR to synchronously clear the counter to 0000 (LLLL).
The !flALS161B and 'AS161 carry look-ahead circuitry provides for cascading counters for n-bit synchronous applications without additional gating. ENP and ENT inputs and a ripple-carry (RCO) output are instrumental in accomplishing this function. Both ENP and ENT must be high to count, and ENT is fed forward to enable RCO. RCO, thus enabled
SN74ALS161B Data Sheet
