Maker Pro
Maker Pro

designing a replacement memory controller w/ memory

K

Keith M

Jan 1, 1970
0
I have a 68030 accelerator card that connects to an optional RAM
expansion card. I'd like to design a compatible larger memory
expansion card. This memory card contains an onboard DRAM memory
controller made by QLogic. I can hopefully reverse engineer the
pinouts for the connectors (two 50-pin header connectors) between the
accelerator card and the RAM expansion card by tracing. I have a
smaller capacity card for comparison.

I'm thinking of using a small FPGA board with SRAM memory, but I'm
open to other ideas. The requirements are:

32-bits wide data
8MB ram.
60-80ns response time
Easy to source components in low quantities in the US
Relatively easy to implement (i'm trying KISS here)
low(er)-cost (no profit potential here)

I'm guessing that the addresses that will appear on the address bus
will be arriving to my replacement memory controller shifted (is the
word mapped?) to some particular range, and that I'll need some type
of lookup table to map those addresses to 0-based address bits on the
memory itself. Right?

Is this plan reasonable? The software that configures the OS for the
memory can be setup to accept 8 megs, so I'm not horribly worried yet
about how the OS-side of things is going to be handled.

Thanks

Keith
 
I have a 68030 accelerator card that connects to an optional RAM
expansion card. I'd like to design a compatible larger memory
expansion card. This memory card contains an onboard DRAM memory
controller made by QLogic. I can hopefully reverse engineer the
pinouts for the connectors (two 50-pin header connectors) between the
accelerator card and the RAM expansion card by tracing. I have a
smaller capacity card for comparison.

I'm thinking of using a small FPGA board with SRAM memory, but I'm
open to other ideas. The requirements are:

32-bits wide data
8MB ram.
60-80ns response time
Easy to source components in low quantities in the US
Relatively easy to implement (i'm trying KISS here)
low(er)-cost (no profit potential here)

I'm guessing that the addresses that will appear on the address bus
will be arriving to my replacement memory controller shifted (is the
word mapped?) to some particular range, and that I'll need some type
of lookup table to map those addresses to 0-based address bits on the
memory itself. Right?

Is this plan reasonable? The software that configures the OS for the
memory can be setup to accept 8 megs, so I'm not horribly worried yet
about how the OS-side of things is going to be handled.

Thanks

Keith

Check voltage levels on modern parts, eh? There's a lot of low voltage
stuff these days.
Also look into pseudo-static RAM, it is self-refreshing DRAM that
looks like a SRAM.
Modern parts do come in BGA packages though, less friendly for the
hobbyist.
 
K

Keith M

Jan 1, 1970
0
Check voltage levels on modern parts, eh? There's a lot of low voltage
stuff these days.

Good idea. Is most stuff 3.3v now? I've seen "5v tolerant" listed
before on low voltage parts.
Also look into pseudo-static RAM, it is self-refreshing DRAM that
looks like a SRAM.

Any downside like lack of speed or anything?
Modern parts do come in BGA packages though, less friendly for the
hobbyist.

Yuck. If I'm serious about this I'm going to have to get used to
higher density parts because I'm going to be dealing with a minimum of
24 address and 32 data pins, so 56 pins w/o control leads, etc. I've
considered schmartboards for breaking some of that stuff out. I've
never made my own custom pcb, perhaps this will be the first.

I'd love to find an FGPA with either built-in ram, or a small
reasonably-priced eval board that includes the ram (and hence likely
supported with a free ram controller ip core) and a header for 60-70
pins.

Prototyping high pin count stuff though seems difficult for the
hobbyist.

Thanks

Keith
 
Good idea. Is most stuff 3.3v now? I've seen "5v tolerant" listed
before on low voltage parts.

3.3V is a relatively high voltage these days.
Any downside like lack of speed or anything?

Not for a 68030 I think.
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=CA&keywords=psram&x=0&y=0
Yuck. If I'm serious about this I'm going to have to get used to
higher density parts because I'm going to be dealing with a minimum of
24 address and 32 data pins, so 56 pins w/o control leads, etc. I've
considered schmartboards for breaking some of that stuff out. I've
never made my own custom pcb, perhaps this will be the first.

I wonder if there's a market for packaging modern parts onto a PCB for
hobbyists.
Sounds like a plan.
Prototyping high pin count stuff though seems difficult for the
hobbyist.

Thanks

Keith

But not impossible. If you make a PCB with soldermask and use
ministencils with solderpaste, you can reflow in a toaster oven.
 
J

JosephKK

Jan 1, 1970
0
Check voltage levels on modern parts, eh? There's a lot of low voltage
stuff these days.
Also look into pseudo-static RAM, it is self-refreshing DRAM that
looks like a SRAM.
Modern parts do come in BGA packages though, less friendly for the
hobbyist.

Scope error. OP is not talking about 8 GB of ram but 8 MB of ram.
 
Top