18 Jun
2008
18 Jun
'08
11:44 a.m.
Allison wrote:
Thats pretty crufty.
I suppose. I thought it was a clever way to keep the cost and size
of the controller to a minimum, as opposed to implementing DMA. Other
than the Motorola MC6844, which was expensive and not readily available,
there weren't any DMA controllers that were easy to interface to the
synchronous bus of a 6502. I could have built a DMA controller out
of TTL, but it would have been quite a few chips, and might not have
fit on the PCB without going to four layers. I could have added a
local processor running at a higher clock. Any of those approaches would
have been a lot more expensive.
Eric