DM74LS163A Datasheet | Fairchild Semiconductor

Description These synchronous, presettable counters feature an internal carry look-ahead for application in high-speed counting designs. T he D M74LS161A a nd D M74LS163A ar e 4- bit binary counters. The carry output is decoded by means of a N OR ga te, thus pr eventing spi kes d uring th e n ormal counting mode of operation. Synchronous operation is provided by having all flip-flops clocked simultaneously so that the outputs cha nge coincident w ith ea ch oth er when so instructed by th e co unt-enable i nputs and i nternal gating. This mod e o f ope ration e liminates the o utput co unting spikes which ar e no rmally associated w ith asyn chronous (ripple clock) cou nters. A buffered clock input tr iggers t he four fl ip-flops o n th e r ising (positive-going) ed ge of t he 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 a gree with the setup data after the next clock pulse, regardless of the levels of the enable input. The clear function for the DM74LS161A is asynchronous; and a low level at the clear input sets all four of t he flip-flop outputs L OW, regardless o f t he levels o f c lock, load, o r enable i nputs. T he c lear fu nction for t he DM74LS163A is synchronous; and a low level at the clear inputs sets all four of the flip-flop ou tputs LOW af ter the next cl ock pu lse, regardless of the l evels o f th e e nable inputs. T his synchronous cl ear allows the co unt l ength to be mo dified easily, as dec oding the maximum cou nt desired can be a cplished w ith on e e xternal N AND gate. T he gate ou tput i s con nected to th e cl ear i nput to synchronously clear the counter to all low outputs. The carry l ook-ahead ci rcuitry provides fo r cascading counters fo r n- bit sync hronous ap plications w ithout additional ga ting. Ins trumental i n a cplishing th is fun ction are...