SSI Asynchronous Counters
-I can create and modify a 3-bit up/down counter.
To the right is a 3-bit up counter, it is a 3 bit counter because there are 3 flip-flops which each hold one bit of information at a time, to modify a 3 bit or any kind of counter you have to change either the amount of flip flops there are, or the clock, or the connections on the falling or rising edges. These change the Maximum Count Number, the Counting Speed and whether or not its an up or down counter, in order. -I can explain why asynchronous counters have a "ripple" effect. Asynchronous counters have a ripple effect because all of the signals require the last signal in the circuit to be completed before the next one can be sent; because they are all wired up in a chain starting with one clock, that allows it to count. Because all of the signals get to the counter at different times there are a few weird counts before all of the signals reach the counter and it shows the true value. -I can explain how to make changes to the count level and starting position. To change the count level you can put a series of gates such as AND gates coming from the signals going to the clear input, you can set the gates so that they only trigger the clears when they are at a certain number, this only works so far as you have enough flip-flops to achieve the number you want, a 3 bit counter has a maximum of 7 which is actually 6 because you have to use the 7 place as a reset point if you want to keep going. To change the starting position you can wire certain flip flops into your preset so that when the whole the resets whichever signal you want to go is already started, then it will start at the count you want. |