The T Flip-Flop (Quickstart Tutorial)

The T Flip-Flop is a flip-flop that may toggle its output. Toggling means switching its output to its reverse; 1 turns into 0, and 0 turns into 1. The sort of flip-flop is commonly utilized in counters and frequency dividers.

On this quickstart tutorial, you’ll be taught the way it works, its reality desk, and methods to construct one.

T flip-flop symbol
T Flip-Flop image

What’s a T Flip-Flop?

Flip-flops are parts generally used to retailer a digital worth on their output. They’ve a Clock (Clk) enter that decides when to replace their output.

The T Flip-Flop is a single-input flip-flop that both holds or toggles its output worth.

Toggling, which is the rationale for the “T” within the title, means altering between two states. If the output is 1, toggling will change the output to 0. If the output is 0, toggling will change the output to 1.

You’ll be able to construct a T Flip-Flop from different flip-flops, for instance through the use of the JK flip-flop and connecting the J and Ok inputs as follows:

T flip-flop circuit made from a JK flip-flop
T Flip-Flop circuit design

Reality desk

Normally, you possibly can set off T Flip-Flops with a falling edge sign, which is the change from a digital state of 0 to 1 ↓, or with a rising edge sign, a change from 1 to 0 ↑. The next reality desk corresponds to a flip-flop that triggers on the rising edge:

Clk T Earlier Q Subsequent Q Description
0 or 1 X Q Q No rising edge
no change
0→1 (↑) 0 Q Q Reminiscence
(no change)
0→1 (↑) 1 0 1 Toggle
0→1 (↑) 1 1 0 Toggle
T Flip-Flop reality desk

You’ll be able to see that if there is no such thing as a rising edge within the Clk enter, it doesn’t matter what you place into the T enter, the Q output will stay unchanged.

One thing just like the earlier case occurs when you have got a 0 within the T enter. Even when the flip-flop is triggered, in case you have both 0 or 1 within the Q output it can keep that manner.

To get the Toggling conduct it’s important to place a 1 within the T enter. What you’ll observe is a change from 0 to 1 or from 1 to 0 each time the flip-flop is triggered. You’ll be able to see this conduct within the timing diagram under:

T flip-flop timing diagram
A timing diagram for the T Flip-Flop

Constructing a T Flip-Flop Circuit

You’ll be able to construct a T Flip-Flop simply by shorting the J and Ok inputs of a JK flip-flop. Nonetheless, some web sites on the market counsel you construct the circuit like under. However that is an incomplete circuit that won’t work correctly:

Incomplete T flip-flop built from JK flip-flop

On paper, it appears to work. However what most web sites that publish this circuit fail to say is that you just want a really brief clock pulse for it to work.

Your clock pulse must go excessive, then low once more earlier than the output (Q) adjustments state. In any other case, the Q output will toggle shortly between 1 and 0 throughout your entire constructive pulse period. You’ll be able to see this conduct within the following timing diagram:

Racing problem

This can be a downside known as Racing. However it’s simply solved through the use of an edge-triggered JK Flip-Flop as a substitute.

You may also construct a completely useful T Flip-Flop through the use of a D Flip-Flop mixed with an XOR gate, like this:

Edge triggered T flip flop built from a D flip.flop
Edge-Triggered T Flip-Flop circuit

Instance Circuit: Toggling an LED

As a sensible instance, you possibly can toggle a light-emitting diode (LED) utilizing only one push button, the T Flip-Flop, and a few resistors. Take a look at the circuit under:

Circuit example: One-button light switch with LED

You’ll be able to see how the T enter is linked to 5V, which suggests logic 1. So each time you set off the T Flip-Flop, the Q output will toggle its state.

The Clk enter makes use of a pulldown resistor configuration, which implies that the Clk enter is 0 every time the button is just not pushed. Whenever you press the button PB1, the Clk enter will go from 0 to 1 (rising edge sign).

So each time PB1 is pushed, the LED linked to the output Q activates or off.

To assemble the above circuit you want:

  • 1x T Flip-Flop circuit (ex by combining a CD4013 and a CD4030)
  • 2x 10 kΩ resistor (R1 and R2)
  • 1x 330 Ω resistor (R3)
  • 1x Pushbutton
  • 1x LED


Do you have got any questions on this part? Let me know within the feedback under and I’ll get again to you as quickly as potential.

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