Document
DM74S161 DM74S163 Synchronous 4-Bit Binary Counters
February 1992
DM74S161 DM74S163 Synchronous 4-Bit Binary Counters
General Description
These synchronous presettable counters feature an internal carry look-ahead for application in high-speed counting designs They are 4-bit binary counters The carry output is decoded by means of a NOR gate thus preventing spikes during the normal counting mode of operation Synchronous operation is provided by having all flip-flops clocked simultaneously so that the outputs change coincident with each other when so instructed by the count enable inputs and internal gating This mode of operation eliminates the output 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 the clock input waveform
These counters are fully programmable that is the outputs may be preset to either level As presetting is synchronous setting up a low level at the 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 input
The carry look-ahead circuitry provides for cascading counters for n-bit synchronous applications without additional gating Instrumental in accomplishing this function are two count-enable inputs and a ripple carry output Both countenable inputs (P and T) must be high to count and input T is fed forward to enable the ripple carry output The ripple carry output thus enabled will produce a high-level output pulse with a duration approximately equal to the high-level portion of the QA output This high-level overflow ripple carry pulse can be used to enable successive cascaded stages
Features
Y Synchronously programmable Y Internal look-ahead for fast counting Y Carry output for n-bit cascading Y Synchronous counting Y Load control line Y Diode-clamped inputs
Connection Diagram
Dual-In-Line Package
Order Number DM74S161N or DM74S163N See NS Package Number N16E
TL F 6471 – 1
C1995 National Semiconductor Corporation TL F 6471
RRD-B30M105 Printed in U S A
Absolute Maximum Ratings (Note)
Supply Voltage
7V
Input Voltage
5 5V
Operating Free Air Temperature Range
0 C to a70 C
Storage Temperature Range
b65 C to a150 C
Note The ‘‘Absolute Maximum Ratings’’ are those values beyond which the safety of the device cannot be guaranteed The device should not be operated at these limits The parametric values defined in the ‘‘Electrical Characteristics’’ table are not guaranteed at the absolute maximum ratings The ‘‘Recommended Operating Conditions’’ table will define the conditions for actual device operation
Recommended Operating Conditions See Section 1 for Test Waveforms and Output Load
Symbol
Parameter
VCC Supply Voltage
VIH High Level Input Voltage
VIL Low Level Input Voltage
IOH High Level Output Current
IOL Low Level Output Current
fCLK
Clock Frequency (Note 1)
Clock Frequency (Note 2)
.