Electronic – Selecting external RAM for an ARM static memory controller

armmemorysram

So I'm going through the datasheet for a device by Atmel (AT91SAM) and it shows the followings:

This SMC is capable of handling several types of external memory and
peripheral devices, such as SRAM, PSRAM, PROM, EPROM, EEPROM, LCD
Module, NOR Flash and NAND Flash.

So that's good as I can get SRAM from Digkey, however there are many types: SRAM selection on Digikey.

Which one is the right one? Perhaps several? I remember doing these exercises in the university all the time in micro-computer class, but we never talked about which type of exact memory we're hooking up to the 8086 micro 🙂
I'll appreciate help clearing this up. BTW I see that the bus width is just 8bits so that will also help minimize the selection but the type is still needs determining.

Best Answer

The peripherals listed there typically have "asynchronous" busses -- that is, the simple and familiar type with address lines, data lines, and a couple of control and latch lines. This means that the SMC is not meant to work with SDRAM, DDRAM, or other subspecies of synchronous dynamic RAM: it's meant to work with regular ol' asynchronous static RAM, so that's what you'll probably want to look for.

You can also use PSRAM (Pseudo-Static RAM) with the SMC. PSRAMs are dynamic RAM chips with a controller tacked on that imitates an asynchronous RAM, and takes care of all the messy refresh chores for you. Since they're dynamic RAM inside, they can be very large and relatively cheap. The downside is that they're also slow, like dynamic RAM.

You probably don't want dual-port or quad-port RAM. If you needed it, you would almost certainly be looking for it specifically.