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jbilander / SF500

Spitfire 500, A low-end 14 MHz Accelerator with IDE and 4/8 MB fast RAM for the Amiga 500.
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Question about the memory #5

Open halfaipg opened 2 years ago

halfaipg commented 2 years ago

Hello, sorry for using your github issues page as my newbie training ground, but I am enjoying building the accelerator and I finally got the xilinx working and recognized in ISE. I have yet to acquire the ram though because of high prices. Please help me understand, why does the memory have to be 16mb if we are only using 4mb? And does the memory have to be 5v or will 2.2v-3.6v memory work?

jbilander commented 2 years ago

Hi, the size of memory chips are shown in Megabits not Megabytes. For example 2M x 8 or 1M x 16 means (2 Megabits times 8, or 1 Megabit times 16) hence the chip is 2 MB in size. On this accelerator (SF500) each chip is 2 MB in size so all memory is used. You can choose to only populate with two chips U5,U6 and put a jumper on JP2, 4MB will take you far in terms of WHDLoad gaming on the Amiga.

It is very unfortunate that someone bought all the cheap memory chips from Digikey. You see when I designed this accelerator they where available for only 4 € a piece.

CY62167G-45ZXI

Had I known this would happen I would've bought them all myself and resell for the same price just to make them available, but too late for that now.

Almost everything on the Amiga motherboard runs on 5V TTL logic levels. In order to use memory chips that are 3.3V you would need to have level shifters on every single address- and data line on the bus. otherwise you would let the magic smoke out. Putting level shifters can be done, look for example on the Vampire, but on this accelerator the space is very limited and also the CY62167G-45ZXI were very cheap when I designed the board.

halfaipg commented 2 years ago

Thank you for the explanation. Will this memory work?

https://www.digikey.com/en/products/detail/alliance-memory-inc/M29F160FB5AN6F2/12180105

jbilander commented 2 years ago

Hi,

No, that is FLASH memory (non-volatile) typically used for storage, it has to be asynchronous SRAM (volatile) memory...or you could redesign the PCB to take SDRAM type and implement a SDRAM-controller in Verilog.

halfaipg commented 2 years ago

https://www.aliexpress.com/item/1005003256658439.html

jbilander commented 2 years ago

I think that should work if those CY62167ELL-45ZXI are genuine Cypress chips.