Connecting 2 16-bit SDRAM as one 32-bit SDRAM

[Slina]

Simple question: is this possible without additional HW logic? I have these two 16-bit SDRAMs and I'd hate to use just one of them or to use them as measly two 16-bit SDRAMs. I think I've browsed through all 3200+pages of reference manual and couldn't find anything.

If it's not possible, what is the simplest way to connect them with additional HW logic ICs?

[AVI-crak]

Can.

When reading / writing - all 32 bits of data will refer to a single address. To mask data, NBL0, NBL1, NBL2, NBL3 are used. Each NBLx for eight data bits: either D0-D7, or D8-D15 - cannot be mixed !!!. The order of connecting the bit lines in separate bytes is not important. The order of use of NBLx is not important. This gives some freedom in the layout of the printed circuit board.

There is only one point of polling data bytes - at the time of initialization. But if you have a connection diagram, then changing the program code will not be difficult.

[waclawek.jan]

I don't think that it's that easy. SDRAMs are not SRAMs. I can't quite envisage how would *any* command be handled by any simple connection or simple external hardware.

JW

[AVI-crak]

But that is exactly so.

Data bus 8 bits: NBLx not used, direct addressing.

Data bus 16 bits: NBL0-NBL1 use the logical line of the address A0, all other addresses are shifted to the right on the memory contacts.

Data bus 32 bits: NBL0 ~ NBL3 use logical lines of addresses A0-A1. Address lines A2 - logically connected to A0 on the memory chip. But in reality, displacement occurs at the hardware level. And the address lines are connected A0-A0, A1-A1, probably so that there is less confusion.

Lines BA0 and BA1 - also use address lines, although they physically perform the switching of memory banks.

[Slina]

Thanks for your replies. Theoretically I know what needs to be done in order to accomplish this, but I was hoping that someone already did that. I'd hate to experiment with this only to find out it's already been done and tested.

[AVI-crak]

There is one crazy project on two-sided 0.6 mm thick fiberglass - using two memory chips.

And a lot of projects on multilayer printed circuit boards. A multi-layer board is much easier to design.

But there are no ready-made projects for download.

You can search for designs in Chinese products. This is just a hint - how to arrange the chips, and connect part of the contacts. There is no complete scheme there.

[Slina]

I have a two layer boards and have already sketched a PCB with two memory chips. It can be done with some tricks. Do you have a link to that project?

[Tesla DeLorean]

If you bit-twizzle the data lines within the bytes you'll need to account for that when you write in the command/mode registers.