Can I use two 16x8 chips in parallel?

[asimonf]

I only have 16x8 parts available from old dual bank ram modules. I'd very much like to recycle old hardware instead of buying new parts. Is it possible?

Cheers!

[nullobject]

Hi @asimonf, have you got a datasheet for your module? I'm happy to take a look and see what's possible.

[asimonf]

@nullobject thanks for the quick reply. Here's the datasheet: https://www.datasheets360.com/part/detail/k4s280832c-tc75/-5923436428586381987/

[nullobject]

@asimonf I have had a look at the datasheet, and it certainly looks possible to adapt the SDRAM controller to work with an 8bit module.

Unfortunately I don't have an 8bit module to test with. Where did you get it from?

[asimonf]

I got in the habit of recycling IC from old equipment that's going to the trash for possible future projects. I've got around 20-30 of those that came from a few old dual rank 256MB PC133 RAM module.

I figured that since most of the signals are similar, these chips were used in old computers in parallel with two of them replacing one 16x16 module and incrementing density that way.

edit: meant to say dual rank memory argh...

[nullobject]

@asimonf I'll see if I can track down a module.

Otherwise, I'll make some changes to the SDRAM core and maybe you can test it out? What kind of FPGA dev board are you using?

[asimonf]

I have both an Altera Cyclone II and an Altera Cyclone IV. Both are entry-level boards, though the Cyclone IV board does have a 16x16 SDRAM available, but I would like to use the core with the Cyclone II board. Even if not two modules at the same time, saving 8 pins would still be worth it.

[nullobject]

Have you tried wiring up two 8-bit chips in parallel to the SDRAM controller? You could send the upper-byte of the 16-bit word to one chip, and the lower-byte to the other?

The other signals from the controller should be sent to both chips.

As far as I can tell, this should work. The only issue may with some of the timing values for these older chips, but you can adjust them by passing different values to the generic inputs of the SDRAM controller.

I'll order some 8-bit chips myself and try this out.

[asimonf]

I will try. There are 16x4 chips available too, but I have none with me. These were available in server ram modules configured in quad rank operation. Aside from Amy buffering issue that might happen due to having to drive so many modules, I see no reason why it shouldn't work.