|Sıralı Mantık Devreleri|
|Sıralı Mantık Devreleri||Shift Register||T-tipi Flip Flop|
|JK Flip Flop||Johnson Ring Sayıcı||D-tipi Flip Flop|
Throughout this tutorial on sequential logic, we found that a Flip Flopwill remain in one of its two stable state indefinitely until some kind of external trigger pulse is applied to change its status. In today's article, we will also review flip flop conversions.
Flip Flops are bistable devices, so these sequential circuits are sometimes called "latches". Because their output is locked in their input state until there is another change in the input state.
We also learned that bistable Flip Flop is the most basic storage element in a sequential logic circuit. We found that it can be configured to produce simple memory elements by connecting two reverse doors to generate feedback. Note that the combinational logic circuit does not require any memory and therefore does not use Flip Flop. However, sequential logic circuits have memory and therefore use various Flip Flop designs to remember their current state. Connecting digital logic doors to produce a memory device leads to applications such as key debounce circuits, shift register counters, etc.
The most basic way to create a single-bit Flip Flop is to use two logical NOR gates, as shown. We can obtain it by using cross-connected doors and feeding the exit from one door to the entrance of another (entrances and exits can be changed). The circuit will have a closed loop (positive feedback). Therefore, the output depends on the condition of the inputs and makes the circuit sequential.
Flip Flop also belongs to a category of digital switching circuits called Multivibrators. The basic bistable multivibrator is a type of regenerative circuit with two active digital doors. Thus, when one digital door is transmitted, the other door is cut off, and vice versa. Since one of these two digital doors is complementary to the other, it produces two stable outputs, both high and low.
Basically, there are four different types of flip flops, and these are:
- Set-Reset (SR) flip-flop or latch
- JK flip-flop
- D flip-flop
- T flip-flop
That is why to help us better understand the different types of Flip Flops available, the following important information shows us how we can convert Flip Flops from one type to another.
Flip Flop Conversions
SR Flip Flop
The simplest of all bistable latches and bistable multivibrators is set-reset (SR) Flip Flop. Basic SR Flip Flop is an important bistable circuit because all other types of Flip Flop are built from it. The SR Flip Flop is manufactured using two cross-connected digital NAND gates, such as the TTL 74LS00, or two cross-connected digital NOR gates, such as the TTL 74LS02.
It is often said that SR bistable and Flip Flops are transparent because their output immediately changes or responds to changes in their input. In addition, SR Flip Flop is considered asynchronous sequential logic circuits, as they consist of digital logic gates along with feedback.
Basic NAND And NOR SR Flip Flop
Above are two basic configurations for the asynchronous SR bistable Flip Flop, which uses a negative input NAND door or a positive input NOR door. Using two cross-connected NAND gates for the SR, the bistable latch works with both inputs, which are normally high in the logic level " 1".
When the R is kept high, a low application at the logic level "0" to the S input causes the Q output to be high and the latch (Latch) to be adjusted. Similarly, the logic level "0" in the R input with a high s input causes the Q output to drop and the latch to be reset. The S = R = 0 condition is prohibited for the SR NAND door latch.
When the output for converting Flip Flops using two cross-connected NOR doors is Q = 1 and Q = 0, it is said that the bistable latch (Latch) is in the SET state. When Q = 0 and Q = 1, the NOR door latch is said to be in reset state. Then we can see that the work of NOR and NAND gate Flip Flops is basically just complementary to each other.
Active High Flip Flop
The basic SR flip flop above and its active high equivalents are all asynchronous type Flip Flops. In other words, the inputs and the current situation alone determine the next state. As a bit memory storage device, we can ask the two inputs to maintain the current output state, regardless of what it is. The operation of the basic SR Flip Flop can be changed by including an additional input to control the behavior of the bistable circuit.
The conversion of the Flip Flop base circuit can be achieved using two additional Logical AND Gates that enable and disable S and R inputs together with a control input. This new circuit is called clocked or gated SR Flip Flop.
Gated SR Flip Flop
Gated SR flip-flops run sequencing when the output status changes or activates input in response to inputs in the application of only one hour. Since the change in output is controlled by this clock activation input, the Gated SR flip-flop circuit is said to be a "synchronous" flip-flop. Then an asynchronous SR flip-flop does not require hours but requires synchrony.
Gated SR Flip Flop Circuit
EN is connected to one of the entrances to both doors. Enable Input is low, causing low outputs. Any subsequent changes to the inputs have no effect on the status of the flip-flop's Q and Q' outputs.
When the Enable input is high, the doors become transparent. thus, any changes to the S and R inputs change the status of the outputs as before. We can then observe that the logic level "1" (High) or "0" (low) can be stored at gated flip-flop outputs by applying a high value to the enable clock input. While the enable input of this output state remains low, we can see that the inputs can be maintained for any desired period of time, regardless of the state.
D Flip Flop
Type D Flip Flop or data latch (Data Latch) has a single input called "D" or data entry. In addition, the two normal outputs have CLK clock inputs, along with Q and Q. The d-type Flip Flop transfers its digital data between inputs and outputs after a clock pulse delay. Thus, the "D" part is also called the "delay" entry.
Type D flip-flops can be easily constructed from an SR flip-flop by connecting an inverter between the S and R inputs.
Two different circuits are given above for the conversion of Flip-Flops to D-type. The upper circuit is a traditional Gated D type configuration with additional inverter. The sub-circuit works exactly the same way, but without an inverter, it saves money through a door. Using an inverter between inputs ensures that inputs S and R are always a complement that eliminates the undefined condition: S = R = 1.
As a result, the d-type flip-flop is also known as the "transparent latch", since Q output follows the D input when the clock input is high. It transfers the binary information directly to the output and allows it to act as if there is no flip-flop there. In short, it made it transparent.
JK Flip Flop
The JK flip-flop is very similar in many ways to the previous SR flip-flop and is probably the most used of all flip-flop designs. The terms "J" and "K" really don't mean any specific explanation.
We have previously seen that the SR flip-flop has two or possibly three meaningful input combinations. Input sequence of the S = R = 1 combination is not allowed, but can be easily modified to achieve different switching functions.
The JK flip-flop has two inputs, "J" and "K". therefore, all four possible input configurations are valid.
Converting flip-flops to a JK flip-flop is to cross-connect Q and Q' outputs through additional 3 inputs and doors, as shown by the s and r inputs.
If both the J and K inputs are high (if the logic is "1"), Q output will change the status (transition) as long as the clock input (CLK) is high. Therefore, the output will be unstable and this will create a racing problem with the basic JK circuit. This problem is avoided by ensuring that the clock input is only in the logic of "1" for a very short period of time or produces a more complex JK flip-flop circuit called Master-slave flip-flop.
Master-Slave Flip Flops
Converting Flip Flops to a "Master-Slave" configuration involves the addition of a second bistable circuit. It consists of two SR latches that are gradually connected by master-slave configuration. One bistable Flip Flop acts as the master receiving external inputs, while the other acts as a slave and receives its entries directly from the master Flip Flop, as shown directly.
T (Toggle) Flip-Flop
The T-type (toggle) flip-flop is a single input bistable with a process similar to the D-type above. We saw it above with the JK flip-flop configuration. If J = K = 1, its output will change in the implementation of the next clock cycle.
The T-type flip-flop is not commercially available, but can be created from a JK flip-flop (or D-type Flip Flop) by connecting the J input to the K input and both to the logic level "1". When J and K are high, Flip Flop changes the status every time it is triggered at the clock entry. This clock entry is now called "Toggle Input" because the output is "0" and "1" is "0". In short, it reverses its situation.