13 Aug
2013
13 Aug
'13
12:27 p.m.
On Aug 13, 2013, at 14:26, Andrew Lynch <lynchaj at yahoo.com> wrote:
Hi Ryan! Thanks! We need help with a dense, fast
DRAM/SDRAM/DDRx board in the worst way. Phat stacks of DDR RAM in the GBs and that
requires DDR encoder/decoder logic.
Neither John nor I know anything about it other than it is quite complex. I've used
the old school DRAMs (4164) but they are nothing in comparison to DDRx or whatever its
called.
Help! This is an urgent appeal. The S-100 80386 CPU board is basically boned without a
decent RAM board to go along with it. We have an 8MB SRAM board that works and can design
an 32MB SRAM board but that just gets you in the door.
Sophisticated Linux/BSD OS's all require GBs of RAM and 32MB won't even get a
boot screen. Maybe a dirty look from the barest of the bare bones Linux distributions.
Not much else.
I'm glad to help (I do this professionally), but I'm out of town for the next two
weeks. Ping me after that, though; you should be able to at least do some standard 3.3v
SDRAM (not DDR) with a small CPLD. You can do DDR 1/2/3 with small, low-cost FPGAs. All of
this will require surface mount (neither RAM nor FPGAs come in anything else now), but you
could at least use SODIMMs to avoid most work with BGAs.
I can't do the pin math in my head to think if you could use QFP packages for the
FPGA, but I suspect not; this may be something that would be worth doing at an assembly
house, even if just for the SMD components. You're not going to get away without using
surface-mount bypass caps for an FPGA, either.
Long story short, if you can deal with the space provided by standard SDRAM, it's
probably your best bet.
Let me know how I can help. I'm glad to help with schematic and layout in my spare
time. Don't even THINK of touching SDRAM layouts with an autorouter. It will not save
you any time or effort, because you will spend more time cleaning up after it than it
would have taken to hand route it to begin with.
- Dave