# Controling a Clock

Discussion in 'Homework Help' started by CTRL, Nov 26, 2013.

1. ### CTRL Thread Starter New Member

Nov 26, 2013
2
0
Hello there,
I am building a 2-bit parallel load register that is taking inputs from a 4-to-2 binary encoder's outputs and I can't figure out how to control the clock.

The register is part of a bigger circuit that takes in an interrupt and holds it for a predetermined amount of time. Once the time period is over, the register is cleared and is ready for another interrupt. To do this, I am suppose to use an encoder and a register.

Could someone explain how to control the clock on a register? I know that you can use the status of the register to do so, but I don't know how to implement it into the circuit. I've attached a couple screenshots of what I have done. One is the register and the other is the project as a whole.

Also, in case what I said didn't make any sense, I've added a description of what I am suppose to do.
Any help is appreciated!

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• ###### Description.doc
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Last edited: Nov 26, 2013
2. ### WBahn Moderator

Mar 31, 2012
18,088
4,917
Why can't you use a free-running clock?

What is the EN input supposed to do?

How are you planning to deal with the "predetermined time" aspect?

3. ### CTRL Thread Starter New Member

Nov 26, 2013
2
0
1. I don't know what a "free-running clock" is. We never worked with that in class.

2. The EN input is the enabler that tells the encoder that the output is the high. In my encoder's case, the high is w3, which is 11, so the encoder outputs w3.

3. With an up/down counter, but we are not suppose to use it for this part of the assignment. I am suppose to build a circuit without it first, make sure that it works, and then use the counter to control the period of time.

4. ### WBahn Moderator

Mar 31, 2012
18,088
4,917
It's just a clock that keep running. Often such a signal comes from a function generator set to produce a squarewave output.

I'm not following this at all. It tells the encode that WHAT output is HI?

If the high is w3, then what are w2 and w1?

And this still doesn't answer the question of what the EN input is for. If the EN input is HI, then what should happen? The encoder should output 11? What should it output if EN is LO?

It would be best if you either put together a table of what the output is supposed to be for all possible input combinations, or draw a timing diagram that should what it should do under various conditions.

So what constitutes the circuit working? Be precise. Imagine that you have to tell someone in the next room, who has your circuit but no idea of what it is supposed to do, what to do and what to tell you in return so that you can determine if the circuit is working.

5. ### ScottWang Moderator

Aug 23, 2012
4,933
777
Using the truth table to show the function of your encoder is more easy to understand what does the decoder working.