Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [ttl]

Transistor Transistor Logic. Logic circuits built from bipolar transistors and resistors.

This tag should be used when talking about digital circuits built purely from bipolar transistors and resistors. Transistor Transistor Logic is the logic that makes up the backbone of most electrical devices today. It's what you would find at the core of an arduino, a computer, or a smmartphone.

559 questions
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Do stateful 74LS series chips start in a defined state?

Specifically, 74161 counters and 74377 registers, can I rely on them to be full of zeros on power on?
Max Zabarka
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Buffering long TTL lines

I'm laying out a stacked PCB where I have 3 or 4 boards stacked on top of each other with signals propogating down with female/male headers (think Arduino shields). Shared control signals are propagating down from the top (logic) board to the lower…
crasic
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Why do 74-series counters label their enable pins T and P?

A few 74-series counter ICs I’ve looked at have two enable pins, and they’re labeled “T” and “P” (for example, the 74LS161A, or 74ALS867A). The “T” input affects the ripple carry out, and the data sheets say this pins are used to enable cascading…
Rick
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What does parallel connection of TTL circuits look like

Here is TTL NAND circuit: My task is to calculate max. number of circuits of same type it is possible to connect in parallel at output of this circuit. It is known R1=4k, R2=1.4k, R3=1k, Vcc=5V, Vce_satuartion=0.2V, Vbe=VD=0.7V, beta_reverse=0.1,…
Igor
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Is an LVTTL output fully compatible to a TTL output?

My company is building a device that is specified to have TTL outputs and I shall test them. Reading about logic levels Wikipedia, EN (the German version has a nice table), I find the voltages of TTL and LVTTL: TTL 5V out: low <= 0.4V , high…
Thomas Weller
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Why do so many logic ICs have output high voltages specified at 3V and 4.5V when they're primarily used at 3.3 and 5V?

I've noticed this a lot, including this recent example. \$\text V_{OH}\$ is specified at 3V and 4.5V, for the maximum and a small output current. I assume this is to allow for 10% load regulation on the 3.3/5V, since those are common rail voltages.…
Matt Young
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Can a transistor's emitter and collector be used interchangeably?

I'm trying to understand the standard TTL NAND Gate in TTL level. But confused with the transistor Q1 operation in the diagram below: Apparently when A and B are together HIGH, the Q1 base-emitter junction is reverse biased. Collector-base…
user16307
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The more ICs I add, the less stable my circuit is. Why is that?

I am making a simple circuit. It has 5 x 74ls161 4-bit counters, and 4 logical ICs (2 x and, not, or). Regardless the logic of my circuit. After I added the last IC (bottom, 74ls32 quad and), the 2nd 4-bit counter stopped working. After 10 seconds,…
Gil Megidish
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Is there a problem with a resistor inline between two TTL gates?

I want to adapt the output of a board to drive additional logic instead of an LED. The driver board has a current limiting resistor before the signal is routed to the connector. Is there any problem leaving the resistor in the circuit? I can modify…
Lee Morgan
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How can I replace a SN74LS04?

I came across Ben Eater's Youtube channel and website and thought I'd give the clock circuit a shot (possibly doing the entire 8-bit computer thing in the future). He conveniently put list of items online what's in the kit. I wanted to order it from…
Bart Friederichs
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Fundamental TTL circuit and its operation

So i am studying TTL circuits and i started with fundamental configuration as shown in the following picture. NOTE: Transistor Q1 is actually a two emitter transistor, i just couldn't find proper symbol when i was drawing this circuit, however,…
cdummie
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Whats the most interesting to build with 7400 series

I'm currently doing a project and have no idea what to build
The lion
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recognising patterns in TTL logic analog circuit

There is a circuit based on TTL( transistor transistor logic I think) . The signals at points A B C D are described. I am new with this TTL, could you help me decompose this united circuit into the logic components which it consists from? Thanks.
Chris95
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What is the function of the latch pin on my 74HC595 IC?

I am using this code with a 74HC595 IC to control a 4 digit 7-segment: digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, LSBFIRST, "value"); digitalWrite(latchPin, HIGH); I understand what the…
Ruben g.
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74LS181: Maximum output current?

It seems that I fried my 74LS181N ALU, though I'm operating on 4.95v and have a 1k resistor (plus LED) on all output pins. I was sure it could handle those 5mA, but the datasheet suggests an output current of max 0.1 mA. Im I misreading the…
Zsolt
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