21
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Why are the outputs of these gates tied together in the Apollo Guidance Computer?
RTL logic is open-collector, which allows the wire-OR connection (in this case, more precisely, wire-NOR.) The characteristic of wire-OR is that gates only drive low, so even if more than one is ...
- 58.5k
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May I connect two open collector outputs in parallel
Yes, this is exactly the intended purpose. It's called a wired-OR or wired-AND, depending on your logic. (Or, as Tony points out, even a wired-NOR!)
However - you should not do this if you just want ...
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12
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Why do I2C lines use open drain driver instead of tri-state drivers?
...as long as the enable signals for the tri-states are mutually exclusive...
The trick is how to do this without adding another wire, or multiple wires to tell each peripheral when it is allowed to ...
- 134k
12
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Difference between no input and a zero input in digital electronics
Usually a Logic Low is a low voltage, normally near Ground/Zero volts, and a Logic High is a higher voltage near the positive supply voltage. There is a range of voltages between Low and High where ...
- 60.8k
9
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Connect two different sources with two Digital Ouptuts using an Adam 4055
I am answering my own question because I think it fits better than updating the question. Feel free to comment I update the post accordingly if it does not suit the EE.SE guidelines.
As @dim ...
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How can I make a non-inverting open-collector (or open drain) with a single transistor?
Just use a low-current SMT Schottky diode in series with the output. Cut the trace and splice the diode in, easy-peasy.
Do it carefully and nobody will notice!
7
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Difference between no input and a zero input in digital electronics
is Low and High used as an indication of lower input voltage and higher input voltage ?
Yes, but some logic families also have current requirements. With TTL, for instance, a logic 0 is not only a ...
- 5,037
7
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Why don't we use decoupling capacitors for open-drain outputs?
Generally with an open-drain output, we use a fairly weak pull-up. Somewhere betweeen 2k and 50k ohms. The stronger the pull-up (the lower the resistance value) the more power would be consumed when ...
- 134k
6
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What is an open collector?
At first glance, the circuit you show looks a lot like a single channel of a ULN2003A 7-channel Darlington driver. Each ULN2003A channel is a Darlington driver: a circuit where one transistor directly ...
- 23.8k
6
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Why are the outputs of these gates tied together in the Apollo Guidance Computer?
how is this any more "poor man's logic gate" than all the rest in RTL? Replace your logic gates in your diagram with the actual transistors and resistors, and you'll see that the output of a ...
- 100k
6
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Tying open-collector outputs to TTL inputs
It'll work without a pull-up, but it will be slow(er) than normal logic for the 0..1 transition, and it will be more sensitive to noise pickup -- it might have spurious transitions if there are nearby ...
- 20.3k
6
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Tying open-collector outputs to TTL inputs
The open-collector output cannot drive the inputs high because the output does not produce a drive current.
So you need a pull-up resistor. The value depends on your switching frequency but 10K should ...
- 23.8k
6
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Why don't we use decoupling capacitors for open-drain outputs?
As hinted in my comment, this is the topic of PDN (Power Distribution Network) analysis.
In general, we model the supply as an impedance, or when considering the ripple/noise between nodes on the ...
- 45.7k
5
votes
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How does the Nintendo 64 detect a controller is connected?
It turns out I wasn't sampling the GPIO long enough. I wrote a little Raspberry PI kernel module to sample the GPIO as fast as possible for 3 seconds, and record a semi-accurate trace. Here's what ...
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5
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Why do I2C lines use open drain driver instead of tri-state drivers?
There are two specific features that require open-drain lines. The first is clock-stretching, where a slave can hold the clock (SCL) low to delay the transaction while it processes data. The second is ...
- 22.3k
5
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Difference between no input and a zero input in digital electronics
I would add that it is possible to design a digital device that can detect an open input vs. high input vs. low input, thus having a three-state input. This is done by alternately connecting the input ...
- 8,374
5
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Why should an open drain/collector comparator go low when pull up is not connected if it is essentially a floating node?
Let us take the example of the MOSFET with open drain.
There are 2 cases:
When VGS << VTH, the drain terminal is indeed a high impedance floating node
When VGS >> VTH,, the drain terminal ...
- 4,390
5
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How can I make a non-inverting open-collector (or open drain) with a single transistor?
I wouldn’t bother with transistors. Single logic gates come in packages the same size as SMT transistors. Just use a single open drain buffer gate. It’s guaranteed to work correctly, it’s a single ...
4
votes
Accepted
Open Collector/Drain vs Push pull
If U1 is also running from 5 V in your example, then it doesn't matter at all. Either way there will be no current thru the LED when the output is not actively pulling low. It won't matter that it ...
- 315k
4
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connecting Open drain and Push pull outputs to drive the same pin
You can use a GPIO as open drain by programming it differently.
If you leave it programmed to output mode, then set the output data to 0 or 1, it behaves as a push pull output.
If you leave the ...
- 174k
4
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Are activated open-collector and open-drain circuits wasting energy?
What puzzles me is that it seems inefficient. In order to switch the output off, I need to effectively short the circuit in order to pull it to ground. Is my interpretation correct? If not, why not?
...
- 180k
4
votes
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When using an open-drain output to drive an NPN transistor, can the base resistor be replaced by a pull-up?
Maybe, but you need to ensure that the Vol from the open-drain output guaranteed to be sufficiently low to ensure that the transistor is fully off under worst-case conditions with the value of R1 that ...
4
votes
Difference between no input and a zero input in digital electronics
Zero’s and one’s (low & high) are digital defined by analog values with a margin in between for transitions and noise.
No output is floating or called tri-state used on bidirectional busses.
...
- 148k
3
votes
Accepted
How connect a open collector output to led and to GPIO?
If the ATMega328p is operated from the 3.3V supply, you can connect them directly, but you should enable pullup resistors in the ATMega, because the voltage drop of the LED may be high enough that the ...
3
votes
Accepted
Are activated open-collector and open-drain circuits wasting energy?
You are correct (except that when the LED is activated, the phototransistor gate is injected with current. It's the opposite logic of what you said). It has it's uses though such as flexible output ...
- 57.3k
3
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Why is there no open-collector OR-gate in the 7400 series?
I don't genuinely know the answer to your question, but I can speculate that it's because there are (quad) open-collector NAND and NOR gates, which are universal gates, and you can relatively easily ...
- 22.9k
3
votes
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Voltage protection of PNP Open-Collector Pull-Down Resistor Circuit
Going with some of your ideas, it could be just this:
simulate this circuit – Schematic created using CircuitLab
The 1.5k comes from 0.4V/250uA as pointed out by Bruce Abbott of the NI 9401 ...
- 3,674
3
votes
Open Drain Serial TX output on Arduino
This is messed up a number of ways:
You say the digital output is open drain, but you have provided nothing that will make the signal go high, ever.
A 60 V 55 A MOSFET is gross overkill here. At ...
- 315k
3
votes
What is an open collector?
The schematic you show is a partial schematic of a ULN2003A or similar Darlington driver array. COM is a common rail (typically) used for the catch (flyback) diodes when inductive loads are being ...
3
votes
Accepted
Minimizing pulled open collector output rise time on 74LS09
10% to 90% rise time is approximately 2.2RC so with your 10K pullup a 2.4usec rise time implies around 110pF load. Assuming you used 10% to 90%.
If we check the datasheet for the RP2200 Rigol probe:
...
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