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Anyone here have experience with replacing the PSRAM on a model 1 with true SRAM? I tried it with some modern, pin compatible SRAM, and although it does work, it only boots properly in about 1/5 power cycles, the rest of the time it just shows a white screen.
This is the SRAM I used: https://www.alliancememory.com/wp-co.../AS6C62256.pdf
I use 32Kx8 and 8Kx8 SRAM chips taken from old 486 motherboards in Model 1 Segas all the time, and they never have any problem. As far as computers are concerned, PSRAM behaves exactly like SRAM, so you can interchange them for the most part (so long as the speed of the incoming chip is sufficient - usually that is where PSRAM is at a disadvantage).
Did you make sure all the pins were soldered down correctly? (Pay special attention to pin 14 aka Gnd/Vss, an intermittent ground can cause MANY perplexing problems.)
I did notice though that these SRAMs you chose are designed to run at 3v. 5.5v is their maximum tolerance, so running them at 5V doesn't give them a lot of wiggle room in case of surges and transients.
Try some SRAM chips that are rated to run at 5v (and not just rated up to 5/5.5v tolerance). I recommend Cypress CY7C199.
Those modules were hard to find as they're discontinued, but I managed to get hold of some. I'll give it a go and see what happens. Thanks.
Update: They work great! Thanks for the tip, Mr Eep.
Honest question: what's the purpose of it? I mean, any performance benefits or something like that?
Unless you can trick the hardware into stopping doing refresh, nope. So really the only usefulness here is to either replace a dead PSRAM or to use a larger RAM (which at least would be useful with homebrew), but it doesn't seem like the latter case.
@ Xaranar: Yer welcome. :)
@ Barone: PSRAM is simply DRAM that can refresh itself, so it emulates SRAM. It's a usually much cheaper, slightly less power hungry alternative to SRAM. Only problem with it is, it isn't capable of running as fast as 'real' SRAM - at least, not the older chips of the Genesis' vintage.
You can overclock fair bit more with SRAMs compared to PSRAMs. Power use lowers a bit also. When I can I always use SRAMs over PSRAMs and mainly for lower power use.
I thought PSRAMs, with their lower transistor density, consumed less power?
Reading and writing processes are much more involved on PSRAMs and there's also the requirement of refreshing which makes sure there's power use all the time rather than just during any read or write operation.