18-03-2014, 10:04 AM
Asynchronous Counters
Asynchronous Counters.ppt (Size: 319.5 KB / Downloads: 217)
Only the first flip-flop is clocked by an external clock. All subsequent flip-flops are clocked by the output of the preceding flip-flop.
Asynchronous counters are slower than synchronous counters because of the delay in the transmission of the pulses from flip-flop to flip-flop.
Asynchronous counters are also called ripple-counters because of the way the clock pulse ripples it way through the flip-flops.
States / Modulus / Flip-Flops
The number of flip-flops determines the count limit or number of states.
(STATES = 2 # of flip flops)
The number of states used is called the MODULUS.
For example, a Modulus-12 counter would count from 0 (0000) to 11 (1011) and requires four flip-flops (16 states - 12 used).