Will the 70ns chips work for NES games? Since its a faster chip, it will slow down to the speed it needs for the game, correct?
It should work. I don't even know if you can buy the ~250ns speed ROMs that they originally used, anymore.
Everything I've heard on the subject is that it needs to be equal or faster than. So 70ns should be fine.
Tormenter wrote:
Will the 70ns chips work for NES games? Since its a faster chip, it will slow down to the speed it needs for the game, correct?
I wouldn't say "slow down" so much as "have the requested data ready long before the NES needs it"...
The speed rating shows how long it takes for the ROM to put the requested data on the data bus after the read signal is sent. Once it's there, it just sits there until another read. The 2A03 runs at 1.79 MHz and needs a ROM that it can read data from in one cycle. To find out how long a cycle is in seconds (the slowest ROM speed possible) all you need to do is divide one by the amount of hertz. So:
1 / 1,790,000 Hz ~= 0.000000559 s = 559 ns
Your ROM should work.
Yes, but the PPU runs about 3 times faster so ~120 ns chips are needed for CHR ROMs I guess. (altough it's not really an issue it should have made CHR ROMs more expensive back then)