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Why do all the gameboy cartridge mods for nonvolatile save use a type of ram like fram? Why isn't a sufficiently fast eeprom or flash ic used?

EDIT: We all know this is about parallel interface ICs, right?

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    \$\begingroup\$ Why the down vote? \$\endgroup\$ – Alexander M Nov 1 '15 at 20:42
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This sort of thing? https://www.reddit.com/r/Gameboy/comments/3ho3aw/til_that_you_can_replace_the_volatile_sram_in_a/

The trick there is that the FRAM part was seemingly designed as a drop-in replacement with an almost identical pinout to the SRAM chip, and seemingly identical power and timing requirements. EEPROM is usually slower to write, and Flash can only be block-erased.

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  • \$\begingroup\$ Check the italicised part in the question \$\endgroup\$ – Alexander M Nov 1 '15 at 20:57
  • \$\begingroup\$ @AlexanderM: Because of the protocol differences, "sufficiently fast" is not a sufficient condition for EEPROM or flash to work. If you wanted to do that, you'd have to build a circuit around it that emulates the SRAM/FRAM write protocol. \$\endgroup\$ – Dave Tweed Nov 1 '15 at 21:00
  • \$\begingroup\$ Protocol? Like hold chip enable high instead of low? \$\endgroup\$ – Alexander M Nov 1 '15 at 21:05
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    \$\begingroup\$ @AlexanderM Find me a 70ns write speed EEPROM and it would be "sufficiently fast" - but I doubt you can find such a part. \$\endgroup\$ – pjc50 Nov 1 '15 at 22:38
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    \$\begingroup\$ "Page Write Cycle Time: 3 ms or 10 ms Maximum" nope, still 43,000 times too slow. \$\endgroup\$ – pjc50 Nov 2 '15 at 9:55
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From a quick look at Fujitsu's info on their FRAMs, it appears that an FRAM can be dropped in place of an SRAM - they can be read and written just like SRAMs, with no need to erase blocks before writing, or other special ceremonies.

EEPROM and FLASH require erasure before writing, and have long write cycles - you can't write to a FLASH or EEPROM at random as you can with SRAM or FRAM.

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