Discuss AT28C16 EEPROM learning experiments in the UK Electrical Forum area at ElectriciansForums.net
A new AND Gate , a new breakthrough ! But still not good.
Now Im trully desperate. I have NO idea what to do next.
Please see this small video here and tell me what you think.
The discrete diode AND gate will not work because when its inputs are connected to 0V, the output does not become 0V ie logic 0. If you study my diagram you will see that the output of CMOS is like a switch and the two resistors. When the output is logic 0 a current will flow creating a voltage drop Vx and there will be the forward voltage Vf = 0.7V across the silicon diode. Thus Vo = Vx + Vf = Vx + 0.7. For TTL 74LS the maximum voltage which will interpreted as a logic must be less than 0.8V. You can see then that this circuit cannot produce a logic 0 when both inputs either or both inputs are logic 0 - the output will always be greater than 0.8V. It might work if you used germanium diodes which have a Vf of 0.2V. But see my later post about using two 7400 NAND gates.A new AND Gate , a new breakthrough ! But still not good.
Now Im trully desperate. I have NO idea what to do next.
Please see this small video here and tell me what you think.
This, I can do.Swap the cmos AND gate for the circuit shown in the attachment. This circuit makes a 2 input AND gate from two NAND gates. I think you have two TTL nand gates spare in ic J33 a 7400.
counting states 0 to 6 and then resetting and repeating
ok so 4 NAND Gates. Got it.Note well please that the far right gate is a NAND - I missed off its small circle on the output.
The 4 Nand gates are used to make two 2 input And gates. If you study the circuit you can see how first Qa and Qb are combined by And. The output of this And is an input to the second And gate along with Qc. The second and gate produces a logic 1 when Qa, Qb and Qc are all logic 1 to send a reset pulse to R1 and R2.While at this stage... can you explain to me how you think? How is your logic about these logic gates? How did you managed to come to this circuit? The logic before making the circuit ! What you were thinking?
From that entire explanation, what is trully important to me and actually explains a behaviour, a cause and effect if you will, is ONLY this proposition. Try to concentrate on this kind of explanation at least with me. To advance faster and further !!! Its our only goal, right?Why it matters to connect R1 and R2 together is because we have to ensure that the reset inputs go to logic 1 and logic 0 at exactly the same time.
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