On 05/12/2010 03:32, Chuck Guzis wrote:
On 5 Dec 2010 at 2:08, Phill Harvey-Smith wrote:
Comments& sugestions welcome.
Use an ARM CPU. The SD-to-CPU connection is straightforward and you
should have more than enough I/O pins to implement the 4-bit
interface. Since most ARMs have internal PLL clock generators,
getting 60-70 MHz is easy on all but the lowest-end models.
I had considdered that, however this does mean doing fine pitch smd
work, which whilst not really (yet) a problem for me does serve as a
barrier to some members of this list (and the community in general).
SCSI bus drivers should be OC, not totem-pole (so you
can have more
than one device on the bus), so you'll want to use something like an
LS641 for the bus transceiver. You can do active termination with a
2.85V LDO regulator (I like the LM1086) and some 110 ohm resistor
packs.
Humm I used LS240s as that was what the sugested interface circuits in
the Adaptec ACB-4000 and Xebec SCSI to MFM boards used, they are 3
state, and I do HiZ them when I'm not driving the bus, I'll have to try
it with another SCSI drive also on the bus tho.
Many ARMs have built-in external RAM controllers, so
adding a few MB
of RAM for cache is easy. Some offer DMA.
Yep, though again at the disadvantage of having to do SM.
P.S. I'm looking forward to Energy Micro's
Giant Gecko line with 128K
of RAM on-chip.
Just googled them, looks cool.
Cheers.
Phill.
--
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
"You can twist perceptions, but reality won't budge" -- Rush.