| << Chapter < Page | Chapter >> Page > |
If you put a series of pulses 10101010 into a T flip flop, the result is 01100110. [link] makes this clearer.
As you can see from [link] , there are half as many pulses in the output. This is why it is called a `divide by two' circuit.
If we connect T flip flops in a chain, then we make a counter which can count pulses. As an example, we connect three T flip flops in a chain. This is shown in [link] .
When this circuit is fed with a stream of pulses, the outputs of the different stages change. The table below shows how this happens. Each row shows a different stage, with the first stage at the top. We assume that all of the flip flops have 0 as their output to start with.
| Input | Output 1 | Output 2 | Output 3 | Number of pulse | Number in binary |
| 1 | 0 | 0 | 0 | 0 | 000 |
| 0 | 1 | 0 | 0 | 1 | 001 |
| 1 | 1 | 0 | 0 | 1 | 001 |
| 0 | 0 | 1 | 0 | 2 | 010 |
| 1 | 0 | 1 | 0 | 2 | 010 |
| 0 | 1 | 1 | 0 | 3 | 011 |
| 1 | 1 | 1 | 0 | 3 | 011 |
| 0 | 0 | 0 | 1 | 4 | 100 |
| 1 | 0 | 0 | 1 | 4 | 100 |
| 0 | 1 | 0 | 1 | 5 | 101 |
| 1 | 1 | 0 | 1 | 5 | 101 |
| 0 | 0 | 1 | 1 | 6 | 110 |
| 1 | 0 | 1 | 1 | 6 | 110 |
| 0 | 1 | 1 | 1 | 7 | 111 |
| 1 | 1 | 1 | 1 | 7 | 111 |
| 0 | 0 | 0 | 0 | 8 | 1000 |
| 1 | 0 | 0 | 0 | 8 | 1000 |
| 0 | 1 | 0 | 0 | 9 | 1101 |
| 1 | 1 | 0 | 0 | 9 | 1101 |
The binary numbers in the right hand column count the pulses arriving at the input. You will notice that the output of the first flip flop gives the right most digit of the pulse count (in binary). The output of the second flip flop gives the second digit from the right (the `twos' digit) of the pulse count. The output of the third flip flop gives the third digit from the right (the `fours' digit) of the pulse count. As there are only three flip flops, there is nothing to provide the next digit (the `eights' digit), and so the eighth pulse is recorded as 000, not 1000.
This device is called a modulo 8 counter because it can count in eight stages from 000 to 111 before it goes back to 000. If you put four flip flops in the counter, it will count in sixteen stages from 0000 to 1111, and it is called a modulo 16 counter because it counts in sixteen stages before going back to 0000.
The modulo of a counter tells you how many stages (or pulses) it receives before going back to 0 as its output. Thus a modulo 8 counter counts in eight stages 000, 001, 010, 011, 100, 101, 110, 111, then returns to 000 again.
If a counter contains flip flops, it will be a modulo counter. It will count from 0 to .
Counting is important. However, it is equally important to be able to remember the numbers. Computers can convert almost anything to a string of 0s and 1s, and therefore to a binary number. Unless this number can be stored in the computer's memory, the computer would be useless.
The memory in the computer contains many parts. Each part is able to store a single 0 or 1. Since 0 and 1 are the two binary digits, we say that each part of the memory stores one bit .
Notification Switch
Would you like to follow the 'Siyavula textbooks: grade 12 physical science' conversation and receive update notifications?
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|