When looking at a schematic and seeing different gates, how do you know if the designer is using the gate as a positive logic gate or a negative logic gate?
Example: You can use a NOR gate either way
a positive logic NOR gate or a negative logic NAND gate.
The only place that I have come across negative logic is in the " Teledac", a diode programmed computer, built in the 1960s for telemetry use. The negative logic lines were tagged with a little triangle. Its difficult enough remembering the truth table of positive logic without a second set to remember, just putting a "NOT" bar over the signal descriptions I think is enough.
Frank
What circuits or stages uses negative logic? that is simple common circuits or you know of?
What would a designer use an Inverted Clock signal?
Why would a designer want to invert logical signals? I see inverted schmitt triggers a lot in logic circuits
Example is:
You have to invert the logic state when to light an LED , since the pull up resistor is tied to +5 volts right?
When you have to invert the logic state or signal mostly?
When I'm probing around on a logic circuit, I don't understand why a designer would want to invert the logic state or logic signal or Trigger signal or Clock signal
Positive Logic means what combination of the inputs cause the output to be HIGH?
Negative Logic means what combination of the inputs cause the output to be LOW?
Suppose you have a lift control circuit, the switches are:- gate closed and button pressed. So to actuate the motor, both of these conditions must be true. So if the switches provide a +5 V, or a '1' in positive logic you use a AND gate, with the output being a 1. If the switches actually provide a 0V or a '0' in positive logic, then it may be easier to call these signals 1 and use negative logic with an OR gate to give a 0V or a '1' in negative logic terms to actuate the motor.
If you have lots of inputs which are 0 V in their good states it might be worth using negative logic, I prefer to use a load of invertors and use positive logic.
Frank
Schmidt triggers are a specialized form of inverters. they are normally used for changing a slowly changing signal into one with fast edges, i.e. they will turn a sine wave into a square wave.
Frank
Schmidt triggers are a specialized form of inverters. they are normally used for changing a slowly changing signal into one with fast edges, i.e. they will turn a sine wave into a square wave.