Started by ericj, June 06, 2008, 05:22:35 pm
Quote from: Great HierophantHowever, there is a reason why you should wish to consider the X5 over the X7. The X7 was developed before the X5. The Genesis is a console that operates on 5v logic, but the Mega EverDrives use modern chips which operate with 3.3v logic levels. When chips of different logic levels are interacting with each other, there should be level translator chips in the signal path to translate the logic levels accordingly. If this is not done, then the higher voltages from the 5v parts and the lower voltages from the 3.3v parts will cause their counterparts to run out of specification.When the v1 was designed, Krikzz mitigated the issue by using current limiting resistors on all the address and data lines. The theory behind current limiting resistors is that instead of the clamping diodes inside the 3.3v chips dissipating the excess voltage from the 5v source as heat, the current limiting resistors do the job externally to the chips. Heat is the enemy of silicon-based integrated chips. If those diodes break down, then they could cause a short circuit and a voltage spike that could take the flash cart and even perhaps the console itself to the scrap heap.Current limiting resistors limit the most obvious harmful effect, but the ICs are still being over/under volted whenever 1s are being output. The X7 has 2 logic level translation chips, and these chips can handle 16 a piece. Between the address and data lines, the cartridges have access to 40 signals alone, nevermind the additional signals used for other cartridge functions read enable, write enable and chip enable. 8 of the data lines and some other signals are still being serviced only by current limiting resistors. When Krikzz designed the X5 and X3 at a later time, he added a third logic level shifter allowing for 48 signals, which is sufficient to handle all the signals the Mega EverDrive needs.