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DECADE COUNTER:-
A decade counter is one that goes through 10 unique output combinations and then
resets as the clock proceeds further.
Since it is an MOD-10 counter, it can be constructed with a minimum of four flip-
flops.
A four-bit counter would have 16 states. By skipping any of the six states by using some
kind of feedback or some kind of additional logic, we can convert a normal four-bit
binary counter into a decade counter.
A decade counter does not necessarily count from 0000 to 1001. It could even count
as 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 1011, 1100, 0011, …. In this count
sequence, we have skipped 0000, 0001, 0010, 1101, 1110 and 1111.
BCD COUNTER:-
A BCD counter is a special case of a decade counter in which the counter counts from
0000 to 1001 and then resets.
The output weights of flip-flops in these counters are in accordance with 8421-code.
For instance, at the end of the seventh clock pulse, the counter output will be 0111,
which is the binary equivalent of decimal 7.
In other words, different counter states in this counter are binary equivalents of the
decimal numbers 0 to 9. These are different from other decade counters that provide the
same count by using some kind of forced feedback to skip six of the natural binary
counts.
BCD or Decade Counter (Ripple) Circuit:-
A binary coded decimal (BCD) is a serial digital counter that counts ten digits and it resets for
every new clock input. As it can go through 10 unique combinations of output, it is also called
as “Decade counter”. A BCD counter can count 0000, 0001, 0010, 1000, 1001, 1010, 1011,
1110, 1111, 0000, and 0001 and so on.
A 4 bit binary counter will act as decade counter by skipping any six outputs out of the 16 (24)
outputs.
The output of the NAND gate is connected in parallel to the clear input ‘CLR’ to all the flip
flops.
