Re: Todd's ELF-ish gets gets a Video Interface System (VIS) #ELF #Homebrew

taf123
 

In the mean-time, the much awaited 11.3258Mhz crystal arrived.

This, together with a couple resistors and capacitors, and 2 inverters from the 74HC04 chip, will form an oscillator for the VIS. This /2 = 5.6629Mhz, which is pretty damned close to the VIS specified 5.67Mhz.





Of course I had to re-populate all of those sockets before I could test, but I don't have the picture.

Anyways, this oscillator didn't work.  I copied it from the RTC circuit, which only used a 32kHz crystal.  Turns out, this same design can be used at higher frequencies, but the load 220k load resister (the blue one tucked next to the crystal) actually needs to be a capacitor to compensate for the phase shift of the inverter at speed.

Updated it to 39pF and it oscillated just fine.






And that's perddy darned close to 5.67Mhz



That's all the time we have for VIS tonight. 

In the next installment, the PS/2 keyboard interface.



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