A binary counter uses multiple flip-flops depending on the number of bits required. There are two types of counters: synchronous uses a common clock for all flip-flops while asynchronous only clocks the first stage. A twisted ring or Johnson counter is similar to a ring counter but inverts the output of the last stage and feeds it back to the first stage input. This creates a pattern that is twice the length of the shift register and circulates indefinitely. Twisted ring counters are used in applications like walking LED displays and converting square waves to sine waves.

1. Muhammad Anas Sabir
Touqeer Abbas
Asad Khan
DLD presentation

2.  A binary counter uses 2 or more single clocked flip-flops
depending on the number of bits required
 There are 2 types of counters Synchronous and
Asynchronous
 A asynchronous counter uses a single clock at the first stage
 But in a synchronous counter all flip-flops are clocked
together with a common clock pulse

3.  Twisted ring is also referred to as Johnsons
counter
 Johnsons or twisted ring counters are just like the
ring counters
 The only difference is that instead of rotating the
last output (Q) back to the input the ‘not’ of the
last ouput (^Q) is feeded to the first input

5.  Instead of a single clears a twisted ring counters have multiple
clears.
 So to start the twisted counter we give every bit an active low clear
that is 0 and Every bit shifts right on each clock pulse.
 But in the end what we shift in the Q0 position is ^Q.
 So a twisted ring counter moves towards all high bits and then it
moves back to all low bits.
 A 3 bit twisted ring counter has 6 states and a 4 bit has 8 active
states.
 So a twisted ring counter has twice as many states as bit positions.

8.  It is used in walking LEDs.
 It is also used to convert square waves into sine
waves.

9.  Johnson Counter is a modified Ring Counter, where the
output from the last stage is inverted and fed back as
the input to the first stage.
 Pattern of bits equal in length to twice the length of
shift register thus circulates indefinitely.
 These counters find specialist applications, including
those similar to decade counter, digital to analog
conversions, etc.