Oya, I've heard of mega-ROMs

https://www.leadedsolder.com/2024/09/03/msx-megarom-oyanami.html

by zdw • 2 years ago

96 9 2 years ago

Normally, I would expect floating address pins to be completely random, but this was very consistent.

I think “random” assumes some kind of perfect conditions. There will be leakage current to ground, leakage current from Vcc, and the actual threshold between high and low for the input will be some particular value.

Just a quick look at the data sheets for the SN54LS670 from TI, and I see that the output pin leakage current is rated at no more than 20 µA. That’s worst-case, but if you apply Ohm’s law and plug in 3.3 V, you get something on the order of 160 kΩ output impedance. I have a limited understanding of electronics and I’m sure I’m missing something, but I’d expect a lot of the output pins to settle on a reasonably stable voltage when they are turned off. Maybe natural variations in geometry or chemistry will push some pins higher and other pins lower.

You can run an entire CPU core with less than 20 µA current these days, just to give it a sense of scale.

jmann99999• 2 years ago

The detail and knowledge shared in these three paragraphs are why I love Hacker News.

jbverschoor• 2 years ago

The Maze of Galious is such an underrated game in terms of IP.

I had the pleasure of attending MSXGOTO40 last december.

Great explanation what megarom actually means, I never knew

ibizaman• 2 years ago

[About buying a used cartridge] In retrospect, after all this adventure, that doesn’t seem like much, but “spending fifty bucks instead of learning something” is not the name of this blog.

Absolutely love this quote.

wileydragonfly3• 2 years ago

Very interesting post. I played some MSX recently and there’s some good games there. I’m sure I’m going to end up with an MSX2 some day.

I recently started making some SEGA master system cartridges. Your only option there is to destroy a Monopoly or After Burner. :-|

mikepavone2• 2 years ago

Your only option there is to destroy a Monopoly or After Burner.

Not sure what you mean. krikzz sells a Master Everdrive if you want something suitable for multiple games. If you want a single game cartridge for a homebrew release, raphnet has you covered.

The one exception is if you have a Japanese Master System (or Mark III). These have a different cartridge connector that's shared with the SG-1000 and SC-3000 and flash carts are harder to find. You may be able to use a western SMS flash cart with a passive adapter though

wileydragonfly3• 2 years ago

I’ve already got an Everdrive. I like making single game carts. I was unaware of the raphnet product but that’s considerably more expensive than original carts.

Oya, I've heard of mega-ROMs

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