Huntron TRACKER 2700 - Page 104

7-
3
Signatures Of A Digital IC
1. Select the 15V, 10 kΩ
ΩΩ
Ω range.
2. Place or clip the black test lead from the Tracker 2700's Common terminal to the IC's ground
pin. For this example, the ground pin of the 74LS245 is pin 10.
3. Use the red test lead from the Tracker 2700's A test terminal. Probe each pin of the IC and
view its signature on Tracker 2700's LCD display. For this example, pins 2 to 9 and 11 to 18
are all buffer circuits so they will have identical signatures. (Note: This is only for ICs out of
circuit.)
4. Use the red test lead from the Tracker 2700's A test terminal. Probe the enable input pins of
the IC and view their signatures on the LCD 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. Select the 10V, 100Ω
ΩΩ
Ω range. Use the red test lead from the Tracker 2700's A test terminal.
Probe the power supply V
CC
input pin and view its signature on the LCD display. For this
example, the V
CC
pin of the 74LS245 is pin 20.
Buffer pins - 15V,10kΩ
ΩΩ
Ω Enable pins - 15V,10kΩ
ΩΩ
Ω V
CC
Power pin - 10V,100Ω
ΩΩ
Ω
Figure 7-2. Signatures of A Digital IC, 74LS245. Common To Pin 10 (Gnd)
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.).