AMA COMPUTER COLLEGE

AMA COMPUTER COLLEGE

PASIG CAMPUS

EXPERIMENT # 2 & 3

July 18, 2002

EXPERIMENT NO. 2 ( Using TTL Devices )

OBJECTIVES: 1.) To be familiar with the different/various kinds of TTL Logic Families.

2.) To use the various kinds of TTL devices and know the effects.

MATERIALS: 1 – 74__ , 1 – 74__ , 1 – 74__ , 1 – 74__ , 1 – 74__ , 1 – Power supply, 1 – Protoboard, Led ( 1 red, 1 green ), Resistors, Connecting wire.

PROCEDURES: 1.) Connect the necessary materials to the protoboard as indicated and 1 TTL device ( 74__ ) as instructed.

2.) Set the power supply to 5 volts DC.

3.) Check for the connections’ output by looking at the led indicator ( on-off ).

4.) Remove the TTL device and place other devices separately ( 74__ , 74__ , 74__ , 74__ ), and determine the output.

MEASURED VALUES / COMPUTED VALUES:

Because the group’s experiment was a total failure due to reasons too brutal for me to say, there is no data available for measured/computed values. The following data are only approximates or probable results.

TTL Device: RESULT:

74__ led ( ON ) Being in the 74 family, it has a ‘1’ Level Output Current. ( +5V (+/- +5V (+/- 0.5V), 0.4mA, 16mA, 2V, 0.8V, 0.04mA )

74__ led ( OFF ) Being in the 74LS family, it has a ‘0’ Level Output Current. (+5V (+/- 0.5V), 0.4mA, 8mA, 2V, 0.8V, 0.05mA, 0.4mA )

74__ led ( ON ) Being in the 74 family, it has a ‘1’ Level Output Current. ( +5V (+/- +5V (+/- 0.5V), 0.4mA, 16mA, 2V, 0.8V, 0.04mA )

QUESTIONS / PROBLEMS:

CONCLUSION:

TTL devices make use of bipolar transistors. The main distinguishing features of the basic TTL family is that they demand a power rail which is very close to +5V, and they use a relatively high amount of current to drive their logic levels ( below 1V for a logical ‘0’ or ‘low’, and above about 3.5V for a logical ‘1’ or ‘high’ ). A particular characteristic of TTL signals is that the inputs to a gate "float high" — i.e. rise to a logical ‘1’ — if left unconnected. This means that the main requirement for driving a TTL input is to "pull down" the level to near 0V. This typically takes a few milliamps per input. This is usually described by saying that a TTL signal source has to be able to "sink" a relatively large current. Typically, TTL gates take around 10-20 nanoseconds to switch level. Hence we can ‘clock’ TTL and pass bits through the gates at rates up to around 50MHz provided the circuits are designed carefully. With care, speeds approaching 100MHz are possible, but for high speed operation other forms of logic may work better. As with other kinds of integrated circuits there are many variations on the basic TTL family. The original chips have numbers like "SN74xx", where xx is the part number. In general, the most useful series is the SN74LSxx family. These consume much less current that basic TTL and hence are easier on the power supply. The ‘L’ in the title stands for "low power", and the ‘S’ stands for "Schottky" — the kinds of diode used inside the gates to help them run quickly without using a lot of current. (The diodes prevent the transistors inside the chip from ‘saturating’ when turned on and wasting lots of current.)

EXPERIMENT NO. 3 ( Interconnection of Logic Gates )

OBJECTIVES: 1.) To know the characteristics of the different/various kinds of TTL Logic Families, and be able to determine the output or effects of such devices.

2.) To be able to know the advantages or disadvantages if any.

MATERIALS: 1 – 7400 , 1 – 7402 , 1 – 7404 , 1 – 7408 , 1 – 7432 , 1 – Power supply, 1 – Protoboard, Led ( red or green ), Resistors, Connecting wire.

PROCEDURES: 1.) Connect the necessary materials to the protoboard as indicated and 3 TTL devices ( at random ) as instructed.

2.) Set the power supply to 5 volts DC.

3.) Set the connecting wires as indicated in the table:

Connection 1: Connection 2: OUTPUT:

----- 0 ------------ 0 -------------- ? ---

----- 0 ------------ 1 --------------- ? ---

----- 1 ------------- 0 ------------- ? ---

----- 1 ------------- 1 -------------- ? ---

4.) Check for the connections’ output by looking at the led indicator ( on-off ).

5.) Remove the TTL device and place other devices separately, and determine the output.

MEASURED VALUES / COMPUTED VALUES:

Characteristics:

7400 – nand

7402 – nor (reverse)

7404 – inverter

7408 – and

7432 - or

TTL Device Combination Connection OUTPUT:

7400 ,02 & 04 0 0 0 ( off )

1 0 ( off )

0 0 ( off )

1 1 0 ( off )

7404 ,08 & 32 0 0 0 ( off )

0 1 0 ( off )

1 0 0 ( off )

1 1 0 ( off )

7400 ,02 & 32 0 0 0 ( off )

0 1 0 ( off )

1 0 0 ( off )

1 1 0 ( off )

7402, 04 & 08 0 0 0 ( off )

0 1 0 ( off )

1 0 0 ( off )

1 1 0 ( off )

7402, 08 & 32 0 0 0 ( off )

0 1 0 ( off )

1 0 0 ( off )

1 1 1 ( ON )

QUESTIONS / PROBLEMS:

1. Why are the outputs the same in the first 4 combinations ?

2. What is the reason of the different result in the TTL device combination of 7402, 7408 and 7432 ?

CONCLUSION:

Based on our experiment, our initial result was all of the combinations using all connections made the same result; all outputs were 0, or off. As we tried to resolve the problem, we came to the conclusion that some TTL devices WERE DEFECTIVE, so it is almost impossible to make a true and logical conclusion if we can’t use all TTL devices and therefore get real data.

But based on our final combination of 7402, 08 & 32, which had a "1" output when connected at 1 and 1, it is because of a particular characteristic of TTL signals is that the inputs to a gate "float high" — i.e. rise to a logical ‘1’ — if connected, this namely for TTL devices 02, 04 and 32. This typically takes a few milliamps per input.

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