Editing Counter (digital) (section)

===BCD decade counter===

A [[binary-coded decimal]] (BCD) decade counter is a MOD-10 counter that directly represents the count as a binary number in the range 0 to 9. Typically a BCD decade counter will count up from 0 to 9 and then overflow. Because their output value range is identical to that of a decimal digit, BCD decade counters are commonly used to represent decimal digits.

{|class="wikitable" style="text-align:center"
|-
! colspan="5"|BCD decade counter output states
|-
! | State || Q0 || Q1 || Q2 || Q3
|-
! 0
| 0 || 0 || 0 || 0
|-
! 1
| style="background:#0FF"|1 || 0 || 0 || 0
|-
! 2
| 0 || style="background:#0FF"|1 || 0 || 0
|-
! 3
| style="background:#0FF"|1 || style="background:#0FF"|1 || 0 || 0
|-
! 4
| 0 || 0 || style="background:#0FF"|1 || 0
|-
! 5
| style="background:#0FF"|1 || 0 || style="background:#0FF"|1 || 0
|-
! 6
| 0 || style="background:#0FF"|1 || style="background:#0FF"|1 || 0
|-
! 7
| style="background:#0FF"|1 || style="background:#0FF"|1 || style="background:#0FF"|1 || 0
|-
! 8
| 0 || 0 || 0 || style="background:#0FF"|1
|-
! 9
| style="background:#0FF"|1 || 0 || 0 || style="background:#0FF"|1
|}

====Asynchronous BCD decade counter====

The circuit shown below is an asynchronous BCD decade counter. It is effectively a 4-bit binary ripple counter that uses a NAND gate to reset the count to zero (by resetting all flip-flops) when the binary count increments to 10 (binary 1010), thus resulting in 10 output states. As in all asynchronous counters, the stored count is unstable while the external clock propagates through the flip-flop chain (including the reset upon reaching count 10).

[[File:DecadeCounter.jpg|450px|border|An integrated circuit BCD decade counter using JK Flip-flops (74LS112D)]]

====Synchronous BCD decade counter====

The circuit shown below is a synchronous BCD decade counter. Five logic gates are used to implement the next-state logic, thus facilitating faster operation than an asynchronous counter at the expense of additional circuitry.

[[File:4-bit BCD synchronous counter.svg|450px|border|Synchronous BCD decade counter]]