Talk:LaFonera Hardware 32MB SDRAM MOD
From DD-WRT Wiki
 Which type of SDRAM
Hi to all. The original SDRAM chip on the Fonera is a hynix HY57V281620ETP-H which features: 128 Mbit organized as 4 banks x 2 Mbit x 16, 133 MHz An ideal chip needed for the 32MB upgrade may be the hynix HY57V561620ETP-H which is: 256 Mbit organized as 4 banks x 4 Mbit x 16, 133 MHz. Unfortunately is difficult to buy single chips (or small amounts), so we prefer to use PC133 SDRAM modules (like a 512MB PC133 DIMM module - double sided, 8 chips per side - or 256MB PC133 SODIMM module - double sided, 4 chips per side - ). The question is that not all chips from these modules are organized as 4 banks x 4 Mbit x 16. For example, I saw a 512MB PC133 DIMM module with 16 Micron Technology MT48LC32M8A2BB-75 which is organized as 4 banks x 8 Mbit x 8, 133 MHz. Is it possible to do a Fonera RAM upgrade with this chip? (in other words: does the different organization of the same memory size make the difference?)
-> My understanding is that the 4 banks and the x16 is the physical interface to the CPU, so I guess the RAM will need to be of this organization. The "n Mbit" could possibly be increased further, as long as RedBoot is updated to use the additional memory. Kintel 00:54, 19 February 2008 (CET)
 Piggy packing 32MB
I too thought about extending the Fonera's RAM.
However, I would have gone a different route. Since it is quite hard to desolder SMD and you can potentially damage the PCB, I would have tried something like:
- Desoldering or cutting CS# on the original module (in such a way that a wire can still be attached to it)
- Piggy packing the 32MB module on top of it, i.e. solder each pin except CS# to the lower chip.
- pull high the lower chip's CS#
- connect the upper chip's CS# to the PCB
Only thing is I'm not sure that pulling CS# high will actually tri-state the chip's outputs. Maybe you also / instead have to pull CKE low.
just my $0.02
 List of working memory chips
Although I doubt many people have or will complete this modification, I think we should compile a list of working replacements for the original memory chip.
I can hereby confirm that the Micron MT48LC16M16A2-75 (:D) works flawlessly.
But, for some reason the modified OpenWRT distribution that the Fonera is shipped with only shows 16 MB. DD-WRT on the other hand shows it all.
I can confirm A2V56S40BTP by PSC is workin. Found on a TwinMOS 128MB stick with 4 chips. If someone need one, I have some spares.PM me in the forum.