June 05, 2020, 07:50:19 pm

News:

The Wiki is fixed!  Again!Go, log in, add stuff!


Homebrew 4MB RAM Card

Started by stas2k, April 17, 2020, 10:00:44 pm

Previous topic - Next topic

stas2k

April 17, 2020, 10:00:44 pm Last Edit: April 18, 2020, 06:24:44 am by stas2k
Hello forum,
As one of the lucky owners of X68000 SUPER I decided to upgrade my RAM. After looking online for boards to buy, I have found the price to be unreasonable for the RAM(or any) expansion cards for the x68k.

Having looked for any DIY solutions, only one mention of this forum was found about people designing homebrew RAM boards back in the day.

I have decided to give it a go using a bruteforce method of using 8x 512KB 10ns SRAM chips(CY7C1041DV33). Many computers on Retrobrew forum are implemented on SRAM. For address decoding, GAL22V10 could be used. This way the board can be much simpler for a novice like me to implement, as there is no DRAM refresh logic.

Thankfully, schematics are available for the original expansion cards, and those can be used as an inspiration.

Are there any obvious flaws to doing it with SRAM+GALs?

EDIT: The SRAM is 3.3V, but is TTL-compatible and was very cheap.