Logic families

Jorge Nuno · Post by **Jorge Nuno** » Sat Oct 06, 2007 8:43 pm

OK. I just chose a quad nand because the nand is more versatile than the inverter, I might use the other gates for something else...

I know it works well (besides the harmonics problem) because I've already mounted it and saw the wave on a 100MHz scope, that's why I created this topic...

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Oct 06, 2007 8:46 pm

Good luck giving your MD a über OC

Jorge Nuno · Post by **Jorge Nuno** » Sat Oct 06, 2007 8:53 pm

Thanks, I wont be easy becuase my Vcc is around 3.6 Volt, I think it limits the overclockability (!?) of the cpu...

The YM2612 and the MB3514 are powered with 4.2V (anything lower the YM will produce wierd noises)

[OFFtopic]
I did it because my VDP is an ass, it's very hot @5V so I reduced to the minimum possible, (at 3.3V there is some tile corruption and locks)

And the 3.6 voltage makes possible connecting to new devices that only support LVTTL, cool eh?
[/OFFtopic]

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Oct 06, 2007 9:00 pm

My MD1 clone went pretty hot... I put heatsinks on the chips... my MD2 does get only warm...

I had to increase my DCs SH-4 vcore to overclock it... and I guess your 3.6volts will be a problem...

Jorge Nuno · Post by **Jorge Nuno** » Sat Oct 06, 2007 9:03 pm

Well for now it isn't a problem after all and it is running perfectly @ 13MHz, the dotclock...

No graphic glitches, no locks, always sound, so I guess I can push even further hehe..

I am targetting for the highest frequency I can get, while maintaning everything perfect (like it is now).
Probably I won't overclock to an extent of seeing crap on the screen and/or locks every other second...

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Oct 06, 2007 9:08 pm

Well, around 16MHz you'll probably get some issues.... my MD2 VDP goes crazy if the clock is above 14MHz, 10MHz is the most stable...

You may find this interesting : http://epicgaming.us/?p=4

Jorge Nuno · Post by **Jorge Nuno** » Sat Oct 06, 2007 9:42 pm

Wow there are some insane clockings: 25~29MHz!, umm I'm expecting my MD to work flawlessly with a clock of around 16MHz(like you said), but I don't have many crystals... I do have a 16 MHz one though

Best shot would be building a variable frequency oscillator with a varicap diode, but I only have a concept idea, never tried to mount it, I dont even know exactly how to make the circuit... (simulating one at the moment)

What I'm planning to do is building the variable osc, test the ultimate stable frequency, get a crystal can closer but lower to that frequency, mount the oscillator with that 74AC00...

Chilly Willy · Post by **Chilly Willy** » Sat Oct 06, 2007 10:27 pm

You might look at these. The ST1507 or ST1517 would probably suit you, depending on the frequency range you need.

http://www.pericom.com/products/timing/ ... s/vcxo.php

Jorge Nuno · Post by **Jorge Nuno** » Sat Oct 06, 2007 10:44 pm

Yeah one of those would be great, but i'm sure that is expensive as hell, and they are from USA (expensive shipping for 1 unit), so probably I'm going to build one from scratch...