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. One of these flip-flop is usually utilized in counters and frequency dividers.

On this quickstart tutorial, you’ll be taught the way it works, its fact desk, and find out how to construct one.

T flip-flop symbol
T Flip-Flop image

What’s a T Flip-Flop?

Flip-flops are elements 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 may construct a T Flip-Flop from different flip-flops, for instance by utilizing the JK flip-flop and connecting the J and Okay inputs as follows:

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

Reality desk

Normally, you may 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 fact 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 fact desk

You may 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’ve 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 a must 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 may 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 may construct a T Flip-Flop simply by shorting the J and Okay inputs of a JK flip-flop. Nevertheless, 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 simply want a really quick 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 rapidly between 1 and 0 throughout the whole optimistic pulse length. You may see this conduct within the following timing diagram:

Racing problem

This can be a drawback known as Racing. However it’s simply solved by utilizing an edge-triggered JK Flip-Flop as an alternative.

You may as well construct a completely practical T Flip-Flop by utilizing 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 may toggle a light-emitting diode (LED) utilizing only one push button, the T Flip-Flop, and a few resistors. Try the circuit under:

Circuit example: One-button light switch with LED

You may 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 signifies that the Clk enter is 0 at any time when the button is just not pushed. While 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’ve got any questions on this part? Let me know within the feedback under and I’ll get again to you as quickly as attainable.

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