Thread: 68k details
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Old 26 August 2018, 15:15   #220
plasmab
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Quote:
Originally Posted by roondar View Post

So my question becomes: why do you need 100ns RAM to service a system that only accesses memory once every 250ns? The same goes for the Amiga. The system required 150ns RAM. So why is that? Why not just run it with 280ns RAM (which would be much cheaper) and be done with it?

Because to me that just does not add up. Either the 235ns figure is correct for memory accesses and the remaining 15ns are either used by other stuff on the board or as 'headroom', or the 100ns figure is correct and then what the hell does the system do for the remaining 150ns?!


I hope you see why I don't get this. I'm not trying to troll or be rude, but a simple division of 1/clock speed shows that the numbers you quote can't really work without something else taking up a significant portion of time. And if there's a reason for this, I'm more than happy to admit I'm wrong.
OK i think i understand the RAM now. It needs a RAS precharge of another 100ns before you can access it again. Hence you can randomly access it every now and again at 100ns but you need to give it 100ns to recover.. bit misleading number IMHO.

I dont want the amiga to be faster. I wanted the 68000 bus to run faster. My point has never been anything to do with the Amiga really. You could use the 68K in places where you have no video or have any need for DMA etc.
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