# RS flip flop 3 bit Asynchronous counter (urgent)

#### CSharpque

Joined Sep 23, 2011
40
hello
can anyone explain how RS flip flop asynchronous counter work from it is diagram.
i know it count specific event at the time when positive clock plus occur. Ech flip flop have clock signal depend on each flip flop work. But i can't understand from circuit diagram.
It's urgent . help me

#### JDT

Joined Feb 12, 2009
657
Have you got a circuit diagram? Can you post it?

Actually, an RS (Reset Set) flip-flop is no good for a counter. You need "master - slave" flip-flops that have a clock input. Usually called "JK" or "D". These are wired to toggle (change state) on the edge of a clock pulse. Connect a number of these in a string so that each flip-flop is clocked by the output of the preceding one, then you have made an asynchronous counter.

This is called an asynchronous counter because there is always a small delay from the clock edge to the output changing state in every flip-flop. So if there are a number of them in a string then the last one can change state a significant time later.

In a synchronous counter all the clock inputs are wired together so all the flip-flops change state simultaneously. Logic is used to control which ones actually change state. Important where the output of the counter is decoded by more logic.

#### CSharpque

Joined Sep 23, 2011
40
Here is the attachment that contain the circuit diagram for RS asynchronous counter

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#### Zazoo

Joined Jul 27, 2011
114
The inverted and non-inverted outputs of the first SR flip-flop (X and X' respectively) are connected back to the the inputs of the same flip-flop (R and S respectively.)
This connection creates a flip-flop that toggles on each postive edge of the clock - i.e. if the current state is a 1, the flip-flop resets (to 0) on the next postive edge (S=0, R=1). And vice versa.

The inverted output of each flip-flop (X') acts as the clock for the next flip-flop. Since this output is toggling, the same processes occurs for each later stage, but at half the frequency of the previous stage (with the first stage being triggered externally.)
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