Tracker-2800-2800S.pdf - 第77页

77 Pin 1 input Pin 2 output Pin 14 power 20V , 10K  , 200Hz 20V, 10K  , 200Hz 10V, 100  , 200Hz Figure 5-4 . Signatures of a 7404 Hex Inverter. Pin 1 input Pin 2 output Pin 14 power 20V, 10K  , 200Hz 20V, 10K  , 200…

4. Use the red test lead from the Tracker 2800's Signal jack. Probe the enable input pins of the IC and

view their signatures on the signature display. For this example, the enable pins of the 74LS245 are

pin 1 and 19 and will have the same signatures. (Note: This is only for ICs out of circuit.)

5. Change the range to 10V, 100, 200Hz. Use the red test lead from the Tracker 2800's Signal jack.

Probe the power supply V

input pin and view its signature on the signature display. For this

example, the V

pin of the 74LS245 is pin 20.

Buffer pins Enable pins V

Power pin

20V, 10K, 200Hz 20V, 10K, 200Hz 10V, 100, 200Hz.

Figure 5-2. Signatures of a Digital IC, 74LS245. Ground Pin to Test Common

Compare these signatures with other signatures of discrete components such as transistors and diodes.

Note that there are quite a few similarities here.

Signatures for Different Logic Chip Families

There are a wide variety of logic circuit families. Each has its special functions, advantages, and

limitations. They range from TTL and its variations (F, LS, S, etc.), emitter-coupled logic (ECL), to

the complementary metal oxide semiconductor (CMOS) and its variations (C, HC, HCT, VC, etc.).

Comparing Two TTL Logic Families

Although the logic function is the same, there are differences in the circuitry of each logic family.

These differences can be readily seen in their signatures

using the Tracker 2800.

We will illustrate these concepts with the following example of

two hex inverters, a 7404 and a 74LS04 from different logic

families. From the logic diagram below, you can see that they

have the same logic functions and pin order. The difference is that

the LS chip uses Schottky transistors in its internal

construction for increased performance and reduced power

consumption. Note that there are only four types of circuit

connections and therefore only four signatures on this

chip: inverter inputs, inverter outputs, V

and ground.

Figure 5-3. Diagram of 7404 & 74LS04.

Pin 1 input Pin 2 output Pin 14 power

20V, 10K, 200Hz 20V, 10K, 200Hz 10V, 100, 200Hz

Figure 5-4. Signatures of a 7404 Hex Inverter.

Pin 1 input Pin 2 output Pin 14 power

20V, 10K, 200Hz 20V, 10K, 200Hz 10V, 100 200Hz

Figure 5-5. Signatures of a 74LS04 Hex Inverter.

Note the differences between the two logic families. They have the same logic function but different

construction, therefore different signatures. To test one of these chips without another reference chip

available just compare each input's signature with the other five inputs. Similarly, compare each

output's signature with the other five outputs.

CMOS Logic Family

CMOS circuits are constructed differently than TTL circuits. The inputs to CMOS transistors are

capacitive due to the use of field-effect transistors (FET) instead of bipolar transistors used in TTL.

In this example, we will choose a 74HC14 Schmidt

Trigger Hex Inverter. The HC designation means that

it's a member of the high-speed CMOS logic family.

From the block diagram of this part, you can see that it

has only four different circuit functions. They are

inverter input, inverter output, power supply V

input,

and power supply ground.

Do the following to display the analog signatures of a digital IC:

1. Select the 50 and 10V, 60 Hz range.

2. Place or clip the black test lead from the Tracker 2800's Common jack to the IC's ground pin. For

this example, the ground pin of the 74HC14 is pin 7.

3. Use the red test lead from the Tracker 2800's Signal jack and probe each pin of the IC. For this

example, pins 1, 3, 5, 9, 11, and 13 are all input buffer circuits so they will have identical

signatures. (Note: This is only for ICs out of circuit.)

4. Similarly, use the red test lead and probe the output buffer pins 2, 4, 6, 8, 10, and 12. These pins

will have the same signatures. (Note: This is only for ICs out of circuit.)

5. Use the red test lead from the Tracker 2800's Signal jack and probe the power supply V

input

pin. For this example, the V

pin of the 74HC14 is pin 14.

Pin 1 – Input Pin 2- Output Pin 14 - V

Figure 5-7. Signatures of a 74HC14 CMOS Hex Inverter in 50, 10V, 60Hz Range

Figure 5-6. 74HC14 Block Diagram.