COUNTERS

WHY COUNTERS ?

Ans. As clock just generate a pulse similarly counter generates a counting with the help of this pulse.

Note: In counter's we go from LSB to MSB  Q0--Q3
and while writing a sequence from waveform write carefully from MSB --LSB Q3--Q0

ASYNCHRONOUS COUNTER
--These are also Known as Ripple Counter
--As there is a more delay compared to synchronous there fore there comes a gliches in its waveforms
--Moreover in Asynchronous counter there is no combinational circuit in input so here
Tclk>=Tc-->q

Unlike synchronous counter having Tclk>=Tc-->q + Tpd(propogation delay of combination logic)

--In Asynchronous while making waveforms we have to just see the +ve edge of clock
   whereas
  In Synchronous you also have to see waveform of input of flipflop combinational logic apart from +ve edge of clock.

SYNCHRONOUS COUNTERS

These counters saves us from glitch waveforms all outputs in these are having same delay 

--FSM
--MOD COUNTER
--EVEN COUNTER
--ODD COUNTER

3-BIT SYNCHRONOUS COUNTER

4-bit Synchronous Counter

Difficult Synchronous Counter