Counter is a sequential circuit. A digital circuit which is used for a counting pulses is known counter. Counter is the widest application of flip-flops. It is a group of flip-flops with a clock signal applied.
Counters are of two types. The logic diagram of a 2-bit ripple up counter is shown in figure. The toggle T flip-flop are being used. But you can use the JK flip-flop also with J and K connected permanently to logic 1. External clock is applied to the clock input of flip-flop A and QA output is applied to the clock input of the next flip-flop i. It is known as ripple counter because of the way the clock pulse ripples its way through the flip-flops. The flip-flop toggles the output either for every positive edge of clock signal or for negative edge of clock signal.
A 3-bit ripple counter can count up to 8 states. It counts from 0 to 7. It counts down from 7 to 0. So FF-A will work as a toggle flip-flop. CircuitVerse Menu. Binary Numbers.
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Digital sequential circuits
NAND gate method.Last month we introduced the Breadboard One educational electronic projects lab. It is a simple mixed signal circuit which we're using to explain the key elements of typical mixed signal systems.
This is a purely digital component and we'll explain how it works and what its output looks like here. It is a member of the CD family which has been in production for almost 40 years! There are newer logic families with the same functionality such as 74HC but we'll stick with the original. As you would expect, a counter counts. The block diagram shows the layout of the inputs and outputs of this component where Q There are other signals which we're not using in this project as well as power Vdd and ground Vss but we'll list all the signals here as you can easily experiment with them by modifying the circuit slightly if you want.
Internally the counter comprises a set of logic gates configured to implement the arithmetic addition operator grab the data sheet for the full details.Synchronous Counters
Normally the counter increments the 4 bit word Q4,Q3,Q2,Q1 by one every time the clock input is toggled. Q1 of the first are the low four bits and Q Q1 of the second are the high four bits. The CARRY signal is generated each time the counter reaches its limit and "rolls over" to start the count again. There are other ways to connect multiple counters e.
How Boolean Logic Works
J1 allow the counter to be preset with a known value. For each clock cycle at the top of the diagram the four bits cycle in a binary encoded sequence in this case starting at 5, counting up to 15 before being "jammed" to 9 and then counting down to zero and wrapping. We'll explain the operation of this component in a future post. For now it's enough to understand that it shows an analog representation of the 4 bit counter output on Q These signals are shown on BitScope's logic channels Note that it remains high so the counter increments from 0 to 15 before wrapping and starting again.See figure 1 below for a screen shot of the completed design.
This subcomponent was reused 4 times in the main IC logic diagram. An assembly file called 74hc It includes all pins used on the commercial IC except ground and Vcc. Each gate within the design has a few variables assigned to them so that the IC remains flexible and easy to reuse in new projects:.
These variables can be assigned their corresponding time and voltage values using a. These values are then within scope for automatic reuse by the 74HC component and flipflop subcomponent simulations. Below is an example of how parameter assignment can be made as used in the test circuit described next :. All voltage sources are referenced using the same high and low voltages described in the previous section: vhighgate and vlowgate.
These values can be reassigned to all gates, all at once, using the. The 74HC component, subcomponent, assemblies, test circuits, and plot control files can all be downloaded without restriction in their use. The datasheet supplied does have some licensed use restrictions, as defined in its last page.
The reference to the 74HC data sheet from NXP Semiconductors is in no way an endorsement of the company or its products, but it is the most recent and best documented behavior for this device that I have found. Download the files listed above for your LTspice designs all in one zipped directory. You can follow any responses to this entry through the RSS 2. You can leave a responseor trackback from your own site. Name required. Mail will not be published required.
Embedded Components and Tools Blog Center. The logic-low is constructed from a zero voltage component instead of simply being tied to the LTspice global circuit common node ground. Download the Circuits The 74HC component, subcomponent, assemblies, test circuits, and plot control files can all be downloaded without restriction in their use.A very common form of flip-flop is the J-K flip-flop. It is unclear, historically, where the name "J-K" came from, but it is generally represented in a black box like this:.
The 1-to-0 notation means that when the clock changes from a 1 to a 0, the value of J and K are remembered if they are opposites. At the low-going edge of the clock the transition from 1 to 0J and K are stored. However, if both J and K happen to be 1 at the low-going edge, then Q simply toggles.
That is, Q changes from its current state to the opposite state. You might be asking yourself right now, "What in the world is that good for? The fact that J-K flip-flop only "latches" the J-K inputs on a transition from 1 to 0 makes it much more useful as a memory device.
J-K flip-flops are also extremely useful in counters which are used extensively when creating a digital clock. Here is an example of a 4-bit counter using J-K flip-flops :. The outputs for this circuit are A, B, C and D, and they represent a 4-bit binary number. Into the clock input of the left-most flip-flop comes a signal changing from 1 to 0 and back to 1 repeatedly an oscillating signal. The counter will count the low-going edges it sees in this signal.
That is, every time the incoming signal changes from 1 to 0, the 4-bit number represented by A, B, C and D will increment by 1. So the count will go from 0 to 15 and then cycle back to 0. You can add as many bits as you like to this counter and count anything you like. For example, if you put a magnetic switch on a door, the counter will count the number of times the door is opened and closed.
If you put an optical sensor on a road, the counter could count the number of cars that drive by. In this arrangement, the value on D is "latched" when the clock edge goes from low to high. Latches are extremely important in the design of things like central processing units CPUs and peripherals in computers.
How Python Works. How to Uninstall Programs in Windows. Prev NEXT. The J-K Flip-Flop. It is unclear, historically, where the name "J-K" came from, but it is generally represented in a black box like this: In this diagram, P stands for "Preset," C stands for "Clear" and Clk stands for "Clock. J-K flip-flop can be used to create and edge-triggered latch, which is important to the design of CPUs.The 4-bit counter starts incrementing from 4'b to 4'h and then rolls over back to 4'b It will keep counting as long as it is provided with a running clock and reset is held high.
The rollover happens when the most significant bit of the final addition gets discarded. When counter is at a maximum value of 4'b and gets one more count request, the counter tries to reach 5'b but since it can support only 4-bits, the MSB will be discarded resulting in 0.
The design contains two inputs one for the clock and another for an active-low reset.
Ring counters (Johnson Ring Counter)
An active-low reset is one where the design is reset when the value of the reset pin is 0. There is a 4-bit output called out which essentially provides the counter values. The module counter has a clock and active-low reset denoted by n as inputs and the counter value as a 4-bit output. The always block is always executed whenever the clock transitions from 0 to 1 which signifies a rising edge or a positive edge. The output is incremented only if reset is held high or 1, achieved by the if-else block.
If reset is found to be low at the positive edge of clock, then output is reset to a default value of 4'b We can instantiate the design into our testbench module to verify that the counter is counting as expected. However we do need to have internal variables to generate, store and drive clock and reset. For that purpose, we have declared two variables of type reg for clock and reset.
We also need a wire type net to make the connection with the design's output, else it will default to a 1-bit scalar net. Clock is generated via always block which will give a period of 10 time units.
The initial block is used to set initial values to our internal variables and drive the reset value to the design. The design is instantiated in the testbench and connected to our internal variables, so that it will get the values when we drive them from the testbench.
Same data recirculates in the counter depending on the clock pulse. Ring counters are of two types. The ring counter is a cascaded connection of flip flops, in which the output of last flip flop is connected to input of first flip flop. In ring counter if the output of any stage is 1, then its reminder is 0. The Ring counters transfers the same output throughout the circuit.
That means if the output of the first flip flop is 1, then this is transferred to its next stage i. By transferring the output to its next stage, the output of first flip flop becomes 0.
And this process continues for all the stages of a ring counter. Here we design the ring counter by using D flip flop.
This is a Mod 4 ring counter which has 4 D flip flops connected in series. For each clock signal, the data circulates among all the 4 flip flop stages of ring counter. This 4 staged ring counter is called Mod 4 ring counter or 4 bit ring counter. We know that the ring counter is similar to that of the shift registers connected in series. The above diagram shown the four stages of flip flops as the parallel in serial our shift registers, with data inputs D0, D1, D2 and D3.
The data circulation in ring counter is explained below. This input is connected to the first flip flop in the series, so that the flip flop QA is set to 1 and all other outputs of remaining flip flops will be low. This means the data pulse 0 0 1 occurs. In this way, as the clock signal and input of first flip flop changes, the output of the other flip flops changes. As the output of last flip flop in series is connected to the input of the first flip flop, the data sequence rotates or circulates in the ring counter.
For one clock signal, the counter starts its operation. On next clock signal, the counter again resets to Ring counter has 4 sequences:, The timing diagram of the Ring counter will explain that the clock signal changes the output of every stage of the counter, so that CLK signal will help the data to circulate from one flip flop to another.
The state diagram of the 4 bit ring counter is shown in above picture.
It denotes that the position of the preset digit in this case preset digit is 1 is changing its position from LSB to MSB, for one clock signal. The Johnson counter is a modification of ring counter. In this the inverted output of the last stage flip flop is connected to the input of first flip flop.
If we use n flip flops to design the Johnson counter, it is known as 2n bit Johnson counter or Mod 2n Johnson counter. This is an advantage of the Johnson counter that it requires only half number of flip flops that of a ring counter uses, to design the same Mod. The main difference between the 4 bit ring counter and the Johnson counter is thatin ring counterwe connect the output of last flip flop directly to the input of first flip flop. But in Johnson counter, we connect the inverted output of last stage to the first stage input.
The Johnson counter is also known as Twisted Ring Counter, with a feedback. In Johnson counter the input of the first flip flop is connected from the inverted output of the last flip flop. The Johnson counter or switch trail ring counter is designed in such a way that it overcomes the limitations of ring counter.This is our complete and definitive guide to digital counters and all their types. In addition to learning about counters, we are going to understand the difference between up-counters and down-counters.
At least just one that matters. An up-counter counts events in increasing order. A down-counter counts stuff in the decreasing order. An up-down counter is a combination of an up-counter and a down-counter. It can count in both directions, increasing as well as decreasing. Depending on the type of clock inputs, counters are of two types: asynchronous counters and synchronous counters. We will take a look at all the types of counters and their circuits in detail below.
A counter is made by cascading a series of flip-flops. As we know, flip-flops have a clock input. Depending on the type of clock input, counters are of two types. Since counters kind of depend on clocks like all sequential circuits, to understand their working, we will consider every clock cycle.
Meaning, there will be changes in the states of some flip flops at every clock interval. We will try to understand the working in each clock cycle. Mod n or Modulus of n, is a way of referring to the maximum count of a counter. Every counter has a limit with regards to the number they can count up or down to. Mod n expresses that limit.
It is an important label for a counter because it gives us the maximum count of the counter, as well as the number of flip-flops present in the counter. A mod n counter can count up to n events.
We can mathematically represent a mod n counter as.