On 24 May 2010 at 9:46, Ethan Dicks wrote:
That sounds cool. I have a few examples of 5380
implementations
(uVAX2K, Amiga, ISA, 68K Mac...) but I don't think I have one on a
6502. That would be interesting to look over.
The 53C400 datasheet was an eye-opener. When I grabbed a Trantor
T130 card, I was surprised to find that it was a very wierd bird
indeed. The 53C400 can decode all 20 bits of an 8-bit ISA address,
provides for 8 address ranges, as well as handshake for DMA and IRQ
and EPROM chip select. Basically, to do an 8 bit ISA controller, you
need only an LS245, a 2764 EPROM (if you want to boot with it) and
the 53C400. Access is all memory-mapped I/O.
The T130 takes this and turns it on its head with two PALs, making
the 53C400 I/O port mapped (at least partially). It's a needlessly
convoluted design. I wonder if the intention was to emulate an older
5380 design. In reality, there's no reason that a 53C400 design
needs to be any more complicated than a Seagate ST01 or Future Domain
TMC850 design--and I suspect that the two latter controllers are just
variations on the NCR design.
--Chuck