Parallel SDRAM

[majdgh]

Hello everyone,
can someone please help me, how to connect multiple SDRAM like MT48LC4M32B2 in Parallel, I would use STM32F7 with FMC for Example, but what are the pins the should not be connect together.
I have already done an example with 1 SDRAM but i don't want to make the PCB for 2 SDRAM and then figure out that something wrong is connected, because doing such a pcb is not very easy, because of lenghth and impedance matching and at lease 4 Layers, so i wanted to get first help.
so if i connect All Pins in Parallel without CS# then edit the driver to choose which Sdram that i would like to write to, so is this correct or am i missing something here. Thanks for help in advance.

[RoGeorge]

That is a dynamic RAM, so if it is left for more than a few tens of ms without refresh (or without reads - each read also refreshes the read page), then the information stored in that chip will be lost.

CS will deselect the chip, this is correct, but something has to take care of the chip refresh.  Since I never worked with STM32F7 and its FMC, I don't know how the refresh is handled there, but if you just de-assert the CS and let the memory without refresh, it will lose its stored bits.

[majdgh]

Thanks for reply, you made me notice something else. i think even if i edited the driver and change the pins that configure the chip select, the self refresh rate is 4 clock of memory cycles, so if i make it 2 and connect them to together, the mcu may not be able to refresh 2 SDRAMs!