In logic circuit design, we should perform a task after a predefined amount of time on several occasions.
How can we design a timer in for this purpose?
This structure will cope with this question.
A timer is a digital circuit that receives at least two inputs, including a number representing the
number of clock cycles in the timing interval and the start signal, the circuit has an output which
indicates the end of the timing interval.
The idea behind a timer is a straightforward let's assume that the input number is N when the timer
receives a logical value one on the start signal it counts and clock cycles and then activates the end
signal indicating the end of the timing interval if t denotes the clock per.
Then the timing in turmoil is and multiply to.
For example, if it is 10 nanoseconds and is one million, then the timing interval is ten milliseconds.
Now, let's ride the corresponding air telescope we used to find in the state machine technique to implement
the time our state machine has two estates idle and running.
The top function has three arguments, two inputs and one output for define two is static variables,
which will be synthesized into registers in harder.
The first one holds the second state and the second one says the number of lapsed cycles, then based
on our coding style, we should define a few variables to save the registers.
Intermediate values also a variable to keep the design output value throughout the state machine.
Then we have to switch cases, statement to implement the transitions in the state machine.
Finally, the variable values should be assigned to the registers.
As mentioned earlier, the state machine has two states.
Initially, the circuit is in the ideal state when it receives a value of one on the start signal,
it assigns zero to the timer variable and defined the running as the next state.
Otherwise, it stays in the idle state, in the Iranian state, the circuit increments of time or variable
on each rising edge of the clock.
Until the timer variable reaches the value of N minus one, then it activates the end signal and changes
the state to idle.
Let's synthesize and validate this code inviter such as.
First comes the new project.
Choose the basis report as a target of geographical.
Please make sure that we want the IP flow target is selected in the target area.
Now at the design and test bench fines attached to this course as a resources.
Have a look at the design header, unsourced fox.
Opened the source file, it contains the main function, as usual, the status Maribelle has been defined
to keep the correctness of the test.
Three variables are defined as the function arguments.
The first for Loop, which has 20 iterations, calls the timer 20 times, but because the start signal
is zero all the time, the timer doesn't do anything and it is in the idle state.
When the value of one is assigned to the start signal and the design competition is called, then the
value of one is assigned to start signal and the design function is called.
In this case, the timer is simulated for one clock cycle and goes to the running state.
Then the second for loop with 50 iterations calls the timer 50 times while the start is zero.
Therefore, the timer is simulated for 50 clock cycles during the simulation, the timer would be in
the running a state for 90 clock cycles and then goes to the idle state for the rest of the simulation.
No, that as our goal is to inspect the signals and we don't have any specific computation, the code
doesn't check it out.
Therefore, the test sponge always claims that the design is correct.
Let's perform the simulation and check it out.
In the output, we have 20 clock cycles of simulation during which the timer is in the idle state,
when they start signal is when the timer goes to the running state for 20 clock cycles and then activates
the end signal.
If you synthesize the code, we see that the design needs only one clock cycle to finish and iteration.
Now let's perform the TLC simulation.
Don't forget to select the only option for the dumb trace feature, then open the way for viewer.
Please check that there are 20 clock cycles between the rising age of the start signal and the end signals
rising at.
Switch bouncing is an interesting feature of mechanical switches, it can insert several undesired pulses
to a digital system.
How can we bounce a mechanical switch connected to a logic circuit?
The next lecture will address this question.
These are outgoing messages, a digital timer can be described as a sequential circuit that counts the
number of clocks.
To a state of Assam in Etchells can describe a digital timer.
Now, the quiz question, design a 10 minute timer initialised and evaluate that on the basis three
more.