Re: 1551 Repair - 28 pin 6523 Wanted

>Well, TED does it and it works.

The 6566 was designed while they were waiting for fast enough drams to use, 
the 6567 was then hacked so they could get the c64 out of the door. There is 
no real way of determining why they did what they did & it's so long ago 
their recollection is likely to be incorrect.

With TED they had the benefit of hindsight and were able to work with dram 
manufacturers during the design process. It also wasn't designed for speed 
(no sprite dma needed and an additional bad line for colour fetches from 
dram etc).

FWIW the Amiga 1000 ended up using the same scheme as the C64, so agnus only 
controlled it's own access to chip ram. The fat agnus designed for the a500 
had the motherboard multiplexers integrated so it controls all access. The 
A3000 was the same with a bit of extra magic on the motherboard to allow the 
agnus to alternate between two banks of ram so the cpu could have 32 bit 
access to it without a new agnus. For AGA they pushed the magic deep into 
Alice, so dma could fetch 32 bits but the blitter/copper etc were still 16 
bit.


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