Oscillator with 50% duty
Posted: 08 May 2019, 08:08
Hi,
After receiving a Gigatron kit I finished assembling it yesterday late at night. I built a fully socketed one, and this allowed me to do some experimentation regarding its clock oscillator.
First, replacing U1 by a 74HC04 I got a near perfect square wave for the clock. With this clock, and without the delaying capacitor, C3, I could run the Gigatron at 8MHz with a 70ns SRAM (A cypress part, not the 55ns one provided with the kit).
So the easy way to get a square wave in the clock is to replace U1, but what can we do if a 74HCT04 is already soldered without a socket?
Well, a square wave can be achieved by changing the resistor network: The idea is to desolder the 1Meg resistor and to connect it to the two terminals of the crystal, and to add another 1K2 resistor to ground.
These are the waveforms obtained:
After receiving a Gigatron kit I finished assembling it yesterday late at night. I built a fully socketed one, and this allowed me to do some experimentation regarding its clock oscillator.
First, replacing U1 by a 74HC04 I got a near perfect square wave for the clock. With this clock, and without the delaying capacitor, C3, I could run the Gigatron at 8MHz with a 70ns SRAM (A cypress part, not the 55ns one provided with the kit).
So the easy way to get a square wave in the clock is to replace U1, but what can we do if a 74HCT04 is already soldered without a socket?
Well, a square wave can be achieved by changing the resistor network: The idea is to desolder the 1Meg resistor and to connect it to the two terminals of the crystal, and to add another 1K2 resistor to ground.
These are the waveforms obtained: