Open collector outputs may be paralleled since there is no conflict with one out being LOW and other outputs being HIGH.
A logic probe does have a pulse stretcher. This is needed to make a pulse that would be far to short for a human to see long enough to do so.
A logic pulser actually does force a net with a LOW output HIGH, and a HIGH output LOW
Some gates ADD the inputs and other Gates Multiple the inputs
What determines the adding or Multiplying inside the GATE?
A net with two or more outputs.Thanks Chris for the help
What you mean by paralleled?
Net1
Battery1,1
Resistor1,1
Net2
Resistor1,2
LED1,1
Net3
LED1,2
Battery1,2
It stretches a pulse to short for you to see into one that is long enough for you to see. A 10nS pulse might be stretched into a 10mS LED flash or tone. See the datasheet of the probe you are using for it's exact behavior.So what does the pulse stretcher do again? explain more please
It just makes you visually so on the Logic Probes lights alternating?
A scope is FAR better than a logic probe. For instance, the probe will only indicate it saw a pulse, when there might have been 10, or 10,000,000 pulses. A good scope can show you that there were many pulses, their timing and magnitude. That being said, many times a probe is adequate, and I've worked on a lot of circuits with only a logic probe, but there are a lot of little problems that a probe just won't show you. And there is one advantage that a probe has, in that it can differentiate between a LOW and a HighZ state.Is using a Logic Probe better at testing logic levels for TTL and CMOS , VS an oscilloscope?
They do? That is news to me. I've always found both of their outputs to be zero volts. As for telling which family a part belongs to, you just look at it's part number.Because TTL and CMOS have different Logic LOW logic voltages
A zero volt net is Zero volts. There is no way to tell why it's zero just from it's voltage.For me, when looking at TTL and CMOS logic LOW state voltages , I can't tell if the output is Open, DEAD or a low state on an oscilloscope, how can you tell the differences?
10Meg loads a logic circuit? What family of logic are you working with? You might see a 100K resistor used as a pullup, though 10K is more common. How would 10Meg load that? And if the outputs are totem pole types, even a 10K load would not 'load' the net.Also why A logic probe is better at testing logic levels is because the logic probe has the perfect probe impedance for logic outputs VS an oscilloscope it as a 10meg ohm impedance which loads the logic output
Depends on the speed of the scope. But it would have to be a v-e-r-y--- s-l-o-w scope not to be able to see a 1microSecond pulse.A Logic Probe has the Pulse Stretcher circuit so you can use it with a Logic Pulsar for troubleshooting
Since an Oscilloscope doesn't have a pulse stretcher circuit you "can NOT" view the logic pulsars microsecond waveshape in real time for troubleshooting using an logic pulsar right?
What are you talking about?This is for all gates positive logic and negative logic
output Transistor ON = LOW logic level
output transistor OFF= HIGH logic level
Some gates ADD the inputs and other Gates Multiple the inputs
What determines the adding or Multiplying inside the GATE?
Because inside the gates the transistor or mosfet just turns ON or OFF , but what ADDs them or Multiplys the two inputs together to get an output?
.The truth table for gates does not show when it is adding or multiplying the inputs. Instead the truth table says "When either or both inputs are ..
Sounds to me like you are trying to repair unknown boards by testing every chip on them individually.
A Logic Probe has the Pulse Stretcher circuit so you can use it with a Logic Pulsar for troubleshooting
Since an Oscilloscope doesn't have a pulse stretcher circuit you "can NOT" view the logic pulsars microsecond waveshape in real time for troubleshooting using an logic pulsar right?
Depends on the speed of the scope. But it would have to be a v-e-r-y--- s-l-o-w scope not to be able to see a 1microSecond pulse.
Because TTL and CMOS have different Logic LOW logic voltages
They do? That is news to me. I've always found both of their outputs to be zero volts. As for telling which family a part belongs to, you just look at it's part number.
And there is one advantage that a probe has, in that it can differentiate between a LOW and a HighZ state.
It stretches a pulse to short for you to see into one that is long enough for you to see. A 10nS pulse might be stretched into a 10mS LED flash or tone. See the datasheet of the probe you are using for it's exact behavior.
I mean the IC chip internally has a dead output, or dead output stage inside the IC chip which outputs a zero volt potential , it's not a short or open or hi Z , it's just zero volt potentialWhat do you mean by "dead"? Shorted to ground? Shorted to the positive supply? Disconnected?
A TTL input needs up to 1.6mA to make it low so when it is connected to a disconnected output it floats high.
A Cmos input draws no current so when it floats it could be low, high or in between.
Wow you have got to be kidding me.Yes I am and I am trying to test every chip on them individually
the maximum logic low voltage is 0.4V
What parts are you talking about here? There are MSI parts that do math functions, but they are not simple gates.. My manager said that's why they use the + and * signs because the inputs are either adding + or they are multiplying * to get the output
I never thought about it this way, why did they use the + and * signs than?
If you want to see multiple points at the same time, then you need a logic analyzer.I would have to use a DSO digital store scope and would have to STORE every single test point
Once you stored the 10 nanosecond waveform on the DSO, how do you get the PPS Pulse per second measurement? how do you find the pulse rate
I have measured pulse width, duty cycle, but how do you get the pulse rate?
0.5 pps = .5 hz?
I thought we were talking about output voltage levels, not input voltage thresholds. And a logic probe doesn't tell you which is which. The switch just lets you change the threshold level that the probe uses to decide the high or low state. But the voltage that it is looking at has to come from the OUTPUT of the driving device. The only way to actually test what the input threshold is is to use a variable power supply. Start at zero volts and raise it up until the output changes state. The voltage at the input when the change occurs is the threshold voltage.TTL logic Low is 0.75 vdc
CMOS logic Low is 15% of VCC or for 7 volts to 18 volts it's 40% of VCC
A Logic Probe detects the difference between the two because a Logic probe has a TTL /CMOS switch
When using a scope to look at logic you don't care about millivolt levels. For TTL a LOW is anything less than .7 Volts and a HIGH is greater than 2 Volts. For CMOS the levels are ~ half of the Vcc level. Just set the scope channel level for something around 2 to 5 Volts per division. Maybe 10V for high voltage CMOSAn Oscilloscope for me is to had to tell because i have my O- scope input channel .5 or .1 on the knob and it picks up probe noise, O -scope is displaying so much noise because i'm trying to measuring millivolts when measuring logic LOWS.
The probe probably uses a one shot multivibrator. It wouldn't use a sample and hold circuit, as they are generally used for analog measurements, not digital ones.Yes I know, but how does it convert or stretch the 10nSec. into a 10mS? it's a time delaying circuit? sample and hold
ChrisP58 said:TTL inputs usually default to a low input.
ChrisP58 said:A logic 1 on a HighZ output is effectively floating, but should never be left that way. Add a pullup resistor to give it a default level when all of the outputs in the net are HighZ.
0.5pps means it takes 1 second for half a pulse, so it will take 2 seconds for a complete pulse.
I thought we were talking about output voltage levels, not input voltage thresholds. And a logic probe doesn't tell you which is which. The switch just lets you change the threshold level that the probe uses to decide the high or low state. But the voltage that it is looking at has to come from the OUTPUT of the driving device.
.The switch just lets you change the threshold level that the probe uses to decide the high or low state
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