11 Mar
2005
11 Mar
'05
4:22 p.m.
On Fri, 2005-03-11 at 22:10 +0000, Philip Pemberton wrote:
Well personally I prefer logic-only because I know I'll have the parts
here, plus I don't have any sort of programmer for making more exotic
things (ok, so I do have an ancient PAL/EPROM programmer, but without
manuals I've only ever figured out the EPROM side of it :)
But also I think that keeping it simple (and understandable) should be a
goal to enable it to buildable by anyone with a few electronics skills.
If it means it encourages more people to build it and back up classic
media, it's got to be a good thing :-)
OK so four of those would be enough. That's not *too* costly I suppose,
although it probably makes it enough for people to think twice about
it.
I still like the idea of SRAM from old PC motherboards; didn't they
normally have 64 or even 128KBytes? Free then; with other parts costs
it'd probably make the whole thing do-able for a fiver or so (more with
a few frills like a case, PSU etc.)
Presumably
there's no need to have any kind of microprocessor control;
it can all be done with a free-running clock to read from the drive or
write to it, and a few control lines to for read/write, start, stop etc.
Why not stuff it all in a CPLD? Maybe create a logic-only version too... Can static RAM
can't cope with these kinds of speeds? Presumably cache
chips pulled from old PC motherboards would cope happily, even if old
80's parts wouldn't.
70nS SRAM should work fine, and most SRAM is pretty cheap too. I've got a
512kbit here that cost about ?4 and is rated to 70nS IIRC. You're using SCSI in a desktop system? Heh. I
should probably see about
trying that sometime.
Yeah, I bailed on IDE for PC systems about 8 or so years ago and have
only ever used SCSI since. It's nice having the DVD drive, CDROM, DAT
etc. up on the desk and the rest of the machine tucked away underneath.
Handy for imaging old Unix workstation drives too, reading old QIC24
tapes (as per last week when I slogged through heaps of them) etc.
cheers
Jules