All Questions
Tagged with ttl digital-logic
103
questions
6
votes
2
answers
14k
views
Help between 2n2222 and 2n2222a?
I am thinking about ordering this:
http://www.ebay.com/itm/x100-Fairchild-PN2222A-2N2222A-NPN-Small-Signal-TO-92-Transistors-US-Seller-/171520659038?pt=LH_DefaultDomain_0&hash=item27ef6d8e5e
and ...
2
votes
2
answers
146
views
What is a simple circuit to generate TTL signal with fixed frequencies?
What is the simplest circuit that can be used to generate a 5V TTL signal with fixed frequencies such as 0.5Hz, 1Hz, 50Hz, 100Hz, 500Hz, 1kHz, 5kHz, 10kHz..?
- 169k
1
vote
3
answers
118
views
Simple TTL: Is there a way to "detect" a high-z state and easily use that to drive other logic?
I have two TTL style logic chips, call them A and B (*), where the outputs of A are the inputs to B (think: 8 data lines). A has tri-state outputs, so when they are turned off they float. B is an ...
- 7,395
12
votes
4
answers
2k
views
When is it appropriate to mix 74LSxx components with original TTL 74xx?
I spend almost all my tinkering time with 1970s era logic circuits, which use almost all original 7400-series TTL. I do a fair bit of repair and am now starting to design additional logic to work with ...
- 8,561
14
votes
4
answers
2k
views
What logic family is best for general-purpose hobbyist stuff?
I need to buy a few logic ICs. Which family should I get? HC? HCT? Which kind is best to have lying around in a parts box, for maximum compatibility with unpredictable future projects? Wide supply ...
- 96.9k
0
votes
1
answer
355
views
Advantages of using 2 NPN transistor NOT gate
Is there any benefit using 2 NPN transistors for a NOT gate rather than one NPN transistor?
- 17.5k
0
votes
2
answers
144
views
What is the application of the 74LS373?
Looking at the truth table, the data from the D(n) input are directly transferred to the Q(n) output when the high state appears at the C (CLK) input. If there is a low state, there are no data at the ...
- 1,411
0
votes
6
answers
1k
views
Output voltage level of TTL gate
The output voltage level of the TTL logic family is from 0 to 0.4 volts (LOW) or 2.4 to 5 volts (HIGH). Suppose we have a TTL inverter with a square wave of 5 volt amplitude as input (0 volt and 5 ...
- 55.1k
0
votes
0
answers
59
views
What is the quiescent power dissipated by a TTL totem-pole output stage?
In High-Speed Digital Design by Johnson and Graham, the quiescent power of a TTL totem-pole is given as:
$$P_{quies} = \frac{0.4I_{sink} + 1.0I_{source}}{2}$$
I am fairly certain the 1.0 is a mistake ...
- 209
17
votes
11
answers
2k
views
Why was so much TTL logic design "negative true"?
I've been spending time with schematics debugging busted 1970s TTL-based computing circuits. I'm sure this is a more general question but I'll ask it in this context since that's what I'm exposed to.
...
- 7,691
1
vote
3
answers
804
views
TTL logic level: how does a NOT gate check logic level?
This is a TTL logic level checker circuit. The highlighted blue area is a checker pin. Voltage at the checker pin is 0.65 V, so this must be logic 0, the LOW LED will on.
But the input of the first ...
- 9,270
2
votes
2
answers
152
views
Debugging a problematic old TTL pull-up that's not pulling up
I am trying to bring back into operation a late-70s disk controller board (all 74xx TTL). I'm stuck trying to figure out why a small pull-up network is resulting in a far out of spec voltage not doing ...
- 10.5k
1
vote
2
answers
180
views
How worried should I be about a short circuit lasting a couple nanoseconds? [duplicate]
Say I have two driver gates hooked up to each other in the following arrangement:
In theory when A goes low, for a brief amount of time B will be shorted while the 7404 inverter gate switches. Around ...
- 13
3
votes
1
answer
915
views
Why does the 74LS08 see an input logic level even if the inputs are not connected?
I have an 74LS08 (AND gate.) I did not connect any inputs to the IC, but it gives me voltage at the outputs. Should I separate VSS?
- 72.6k
0
votes
2
answers
14k
views
8-bit binary to BCD decoding for three 7-segment displays
I've created a circuit that uses both binary and BCD counters to convert an 8-bit binary number into three BCD numbers, which then feed into BCD to 7-segment decoder chips, and finally to common-anode ...
- 9,270