Group # 5

1. What is the function of pins 2 and 3?

Pins 2 and 3 of the 7490 chip are reset inputs for outputs A, B, C and D or pins 12, 9, 8 and 11 respectively. They will determine partially, along with pins 6 and 7, what the decimal value of the outputs would be.

2. What happens when any of these pins (2 or 3) are raised to logic "1"?

When both pins 2 and 3 are raised to logic 1, and either pin 6 or 7 is in logic 0, the 7490 will reset outputs A, B, C and D to 0 giving us a decimal output of "0". When only one of the pins are raised to logic 1, there are two possible outputs: (1) when either one of pin 6 or 7 is in logic 0, the chip will perform a count or the decimal outputs will cycle from "0" to "9" and (2) when both pin 6 and 7 are in logic 1, the decimal output would be "9".

3. What is the function of pins 6 and 7?

Pins 6 and 7, like pins 2 and 3, are also reset inputs for outputs A, B, C and D. The inputs from these pins will determine if the chip will output a decimal value of "0" or "9" or if the chip will start counting.

4. What happens when any of these pins (6 or 7) are raised to logic "1"?

When either pin 6 or pin 7 is raised to logic 1, two possible outputs will come out: (1) when either pin 2 or 3 is in logic 0, the chip will count and cycle from "0" to "9" and (2) when both pins 2 and 3 are in logic 1, the output will always be the decimal value "0". When both pins 6 and 7 are in logic 1, the output will always be the decimal value "9" no matter what the input from pins 2 and 3.

5. What is the purpose of connecting pin 1 to pin 12?

We connected pin 1 to pin 12 to be able to use the maximum count length, which is a decade or a four bit binary. This makes sure that when the count reaches "9", the count will reset back to "0".

6. What are the output pins?

The input pins of the 7442 IC are pins 15, 14, 13 and 12. These pins accept four high BCD inputs.

2. How did you connect them to the 7490?

The output pins of the 7490, pins 12, 9, 8 and 11, were connected to the input pins of the 7442, pins 15, 14, 13 and 12 respectively.

3. Describe the behavior of the LEDs connected to the outputs of the 7442?

The LEDs connected to the outputs of the 7442 lit up one after the other in the order: pin 1, 2, 3, 4, 5, 6, 7, 9, 10 and 11 as the 7490 performed its count. When the count was 0, the LED at pin 1 lit up because it was low. When the count was 1, the LED at pin 2 lit up because then it was low, and so on until the count reached 9 and the LED at pin 11 lit up. After that, the counting started back to 0 and cycled back again.

The input pins of the 7447 are pins 7, 1, 2 and 6. This IC also accepts four BCD input data.

2. How did you connect them to the 7490?

As seen on the diagram above, we connected the output pins of the 7490 to the input pins of the 7447. Pins 12, 9, 8 and 11 of the 7490 are connected to pins 7, 1, 2 and 6 of the 7447 respectively.

3. Describe the behavior of the LEDs connected to the outputs of the 7447?

Since the 7490 outputs a count from "0" to "9" in BCD format, the 7447 will decode these inputs into active low segment outputs that will then be the inputs of a 7 – segment LED. The 7 – segment LED will then follow the count of the 7490 and segments will light up showing numbers from "0" to "9".

If you were to describe the experiment to your 12-year old younger brother or sister, or to your mother, how would your description read?

In this experiment, we will try to use different chips like the 7490, 7447 and the 7442 and make them count from 0 to 9. We can actually see the chips count from 0 to 9 with the use of Christmas lights and a special chip that has a number 8 on it, which is called a 7 – segment LED. The 7490 chip performs the counting which the lights will follow, but since the lights cannot understand what the 7490 is trying to say, we need to use other chips to translate the counting. For the Christmas lights, the counting needs to go through the 7442 chip and for the 7 – segment LED, the counting needs to go through the 7447 chip. When the counting reaches the Christmas lights, they will light up one after the other then start over again. When the counting reaches the 7 – segment LED, we can actually see the segments of the number 8 light up and form numbers from 0 to 9.