Lab Report Number 2
January 9, 2002
Merry Enriquez
Myron Mariano
Part A - Operating the 7490 counter.
The 7490 is a decimal counter. A decimal counter follows a sequence of ten states and returns to 0 after the count of 9. Such a counter must have at least four flip-flops to represent each decimal digit, since a decimal digit is represented by a binary code with at least four bits. The sequence of states in a decimal counter is dictated by the binary code used to represent a decimal digit. If BCD is used, the sequence of states is as shown in the state diagram below. This is similar to a binary counter, except that the state after 1001 (code for decimal digit 9) is 0000 (code for decimal digit 0).
Pin 1 is a B input that is connected to pin 12, which is the QA output. This connection allows us to use the maximum count length of the 7490, which is 10. This way, the 7490 is able to assume 10 states. This connection also determines that the 7490 will perform a BCD count sequence making the 7490 a BCD Ripple Counter.
The output pins are pins 8, 9, 11, and 12. These pins output a combination of 1’s and 0’s, which correspond, with the binary equivalent of the decimal numbers 0-9, depending on the input level of pins 2, 3, 6, and 7. Pins 2, 3, 6, and 7 are input pins in which pins 2 and 3 perform the reset to zero function and pins 6 and 7 are set-to-nine inputs. Thus, their current input value, whether high or low, dictates what the output or state of pins 8, 9, 11, and 12 will be. This combination of inputs and outputs is shown in the truth table below.
|
Reset inputs |
Outputs |
|
Pin 2 |
Pin 3 |
Pin 6 |
Pin 7 |
Pin 11 |
Pin 8 |
Pin 9 |
Pin 12 |
|
1 |
1 |
0 |
X |
0 |
0 |
0 |
0 |
|
1 |
1 |
X |
0 |
0 |
0 |
0 |
0 |
|
X |
X |
1 |
1 |
1 |
0 |
0 |
1 |
|
X |
0 |
X |
0 |
COUNT |
|
0 |
X |
0 |
X |
COUNT |
|
0 |
X |
X |
0 |
COUNT |
|
X |
0 |
0 |
X |
COUNT |
X = don’t care (may be 0 or 1)
Part B - Operating the 7442 BCD-to-decimal decoder.
The 7442 is a BCD-to-decimal decoder which is a reasonable design decision that makes all outputs equal to 0 when an invalid input combination occurs. The selected outputs are in the 0 state, and all the invalid combinations give an output of all 1’s. This has ten 4-input AND gates.
The input pins are pins 12, 13, 14, and 15, which were connected to the 7490 as shown in the table below. In the respective connections, the 7442 is able to accept four active high BCD inputs and provide ten active low outputs.
|
Pin Connection |
7490 |
7442 |
|
A |
12 |
15 |
|
B |
9 |
14 |
|
C |
8 |
13 |
|
D |
11 |
12 |
The input pins therefore accept different combinations of 1’s and 0’s, which correspond to the binary equivalent of the decimal digits 0 to 15. In this case, the 7442 ensures that all outputs will be 1 when inputs assume binary codes greater than 9. The respective input and outputs are shown in the truth table below.
|
Inputs |
Outputs |
|
Pin 12 |
Pin 13 |
Pin 14 |
Pin 15 |
Pin 1 |
Pin 2 |
Pin 3 |
Pin 4 |
Pin 5 |
Pin 6 |
Pin 7 |
Pin 9 |
Pin 10 |
Pin 11 |
|
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
0 |
0 |
0 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
0 |
0 |
1 |
0 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
0 |
0 |
1 |
1 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
|
0 |
1 |
0 |
0 |
1 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
|
0 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
|
0 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
|
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
0 |
1 |
1 |
|
1 |
0 |
0 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
0 |
1 |
|
1 |
0 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
0 |
|
1 |
0 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
1 |
1 |
0 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
1 |
1 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
With the said truth table, one may be able to determine when the elements connected to the output pins of the 7442 will assume a high level or will be turned on and when they will have a low level or will be turned off. Therefore, in the experiment, since the elements attached to the output pins are LED’s, the LED’s showed an alternating lighting sequence wherein they take consecutive turns in turning off while others are on.
Part C - Operating the 7447 seven-segment decoder.
A seven-segment indicator is used for displaying any one of the decimal digits 0 through 9. Usually, the decimal digit is available in BCD. A BCD-to-seven-segment decoder accepts a decimal digit in BCD and generates the corresponding seven-segment code. In the experiment, this was done by attaching the input pin of the 7447, which are pins 1, 2, 6, and 7, to the respective output pins of the 7490. The pin connections are as follows.
|
Pin Connection |
7490 |
7447 |
|
A |
12 |
7 |
|
B |
9 |
1 |
|
C |
8 |
2 |
|
D |
11 |
6 |
The 7447 IC is a BCD-to-seven-segment decoder/driver. It has four inputs for the BCD digit. Input D (pin 6) is the most significant input and input A (pin 7) is the least significant. The 4-bit BCD digit is converted to a seven-segment code with outputs a through g. The outputs of the 7447 are applied to the inputs of the 7730 (or equivalent) seven-segment display. This IC contains the seven LED (light-emitting diode) segments on top of the package. The input at pin 14 is the common anode (CA) for all the LED’s. a 47 W
resistor to Vcc (pin 16) is needed in order to supply the proper current to the selected LED segments. This set-up therefore results to the truth table as shown below wherein a particular output would light a combination of the Seven Segment to display the pin with the logic set to one. The LED’s, in effect, will display any of the decimal digits 0-9 corresponding to the binary equivalent assumed by the combination of highs and lows in the input pins.
|
Inputs |
Outputs |
|
Pin 6 |
Pin 2 |
Pin 1 |
Pin 7 |
a |
b |
c |
d |
e |
f |
g |
|
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
|
0 |
0 |
0 |
1 |
1 |
0 |
0 |
1 |
1 |
1 |
1 |
|
0 |
0 |
1 |
0 |
0 |
0 |
1 |
0 |
0 |
1 |
0 |
|
0 |
0 |
1 |
1 |
0 |
0 |
0 |
0 |
1 |
1 |
0 |
|
0 |
1 |
0 |
0 |
1 |
0 |
0 |
1 |
1 |
0 |
0 |
|
0 |
1 |
0 |
1 |
0 |
1 |
0 |
0 |
1 |
0 |
0 |
|
0 |
1 |
1 |
0 |
1 |
1 |
0 |
0 |
0 |
0 |
0 |
|
0 |
1 |
1 |
1 |
0 |
0 |
0 |
1 |
1 |
1 |
1 |
|
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
1 |
0 |
0 |
1 |
0 |
0 |
0 |
1 |
1 |
0 |
0 |
|
1 |
0 |
1 |
0 |
1 |
1 |
1 |
0 |
0 |
1 |
0 |
|
1 |
0 |
1 |
1 |
1 |
1 |
0 |
0 |
1 |
1 |
0 |
|
1 |
1 |
0 |
0 |
1 |
0 |
1 |
1 |
1 |
0 |
0 |
|
1 |
1 |
0 |
1 |
0 |
1 |
1 |
0 |
1 |
0 |
0 |
|
1 |
1 |
1 |
0 |
1 |
1 |
1 |
0 |
0 |
0 |
0 |
|
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
Part D - General Observations.
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?
First, 7447 and 7490 are ICs, meaning they receive and process data in the form of pin connections, which by manipulation would show different outputs, sometimes by LEDs or light emitting diodes or a Seven segment decoder in this case. This experiment would like to display the numbers in the 7447 based on the output of the combination of pins. But first, we have to determine which pin goes to which pin of the 7447, using a reference chart. If we connect, say, Pin 1 of the 7490 to a particular slot of the 7447.
|