martinsustek wrote:Hi, it's good news, that idea of Uzebox with 1284 is not dead. I hope that double memory means potential for better games.
But why are you doing it that hard way (instead of changing only ATmega, maybe stabilisator and resistors)? Is the RGB/NTSC chip that problem?
How is it with SCART version? Is there a need for another power source only for chip or whole board can work with raised voltage (eventually with changed resistors in D/A and SD)?
What I want is to change 644 with 1284 in my EUzebox, and I think that it can be done without big adapter and another power source.
The problem with overclocking the ATmega1284 chips is that power needs to be increased. If the power going into the ATmega chip is, for example, around 6 volts which is a stable operating voltage, then the ATmega will output around 6 volts. This means that the video, SPI, audio, and other outputs will have increased voltage and potentially affect other devices. I have experienced this problem with my monitor and with the AD725 chip. When levels for my RGB monitor reach above 5 volts, the image gets quite flickery and slightly washed out. For the AD725, I have had unstable picture once (voltage may have been too high, or breadboard was messed up
). The higher voltage may even affect the controllers, not sure though, but I'm pretty sure they can handle up to 6 at least. The idea of making the expansion was that the base hardware would not have to change design so it can fit in Uzebox, Fuzebox, EUzebox, Uzebox JAMMA, anything else made that fits the 644 40-pin DIP package. I plan to make the expansion a whole lot smaller, this is just a prototype design. With the Uzebox JAMMA, it takes power from the same power line. The Uzebox JAMMA uses a 5 volt regulator to step from 12 volts to 5 volts. The regulator from the expansion boards takes the same 12 volts and steps it to around 5.85 volts, only give the higher power to the 1284 chip, the resistors and other components help step down outputs to 5 volts.
Maybe I could re-do the power circuit to step-up voltage to 5.85 volts instead of regulating the 12 volt line. I noticed that some (or all?) of the Uzebox console designs use a 5 volt adapter.
HardlyUnique wrote:What kind of success rates have you seen?
From previous experimentation, I have had about 95% successful operation at 5.9 volts. When the voltage is lowered to about 5.75 to 5.85, it boots up and displays the logo, then it either keeps resetting, continues with the game, or freezes and displays garbage all over the screen. I will have a schematic soon, I'm still working on the design, not finalized yet.
One final word is the differences in the clock fuses on the chip and different crystal oscillators used makes a difference in success rate during operation, I will make another post about it with more detailed information.
