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View topic - Is there a way to patch a rom to play in English on a Japanese SMS?

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  • Joined: 12 Aug 2019
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Is there a way to patch a rom to play in English on a Japanese SMS?
Post Posted: Sun Jan 28, 2024 4:24 am
For example, running "Zillion" on a Japanese SMS will result in the game in Japanese, regardless of the rom dump. Same with Penguin Land and a few others.

Is this something completely controlled by the BIOS or is there something that can be patched in the rom itself to force it to be in English?
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Post Posted: Sun Jan 28, 2024 8:15 am
It’s entirely done in the game code, it is normally done as seen here:

https://www.smspower.org/Development/RegionDetection
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Post Posted: Sun Jan 28, 2024 7:54 pm
That's good to know, so it should be possible to patch roms to force the region.

Unfortunately I do not know ASM. Is there hex value that should be changed to force USA region, or a tool that you know of that patches region for SMS roms?
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Post Posted: Sun Jan 28, 2024 9:38 pm
No, it’s not as simple as that. It may be possible one up with a hex sequence that can patch out the check in many cases but maybe not all.
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Post Posted: Mon Jan 29, 2024 4:18 am
Maxim wrote
No, it’s not as simple as that. It may be possible one up with a hex sequence that can patch out the check in many cases but maybe not all.


I appreciate the response. I guess like Ringo once said, it don't come easy.
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Post Posted: Mon Jan 29, 2024 7:33 am
out ($3f),a produces hex D3 3F. Overwriting to 00 00 might do the trick. You’d expect to find it only twice, near the start of the ROM; if you find many then patching than all is likely to corrupt the game.
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Post Posted: Mon Jan 29, 2024 4:52 pm
Maxim wrote
out ($3f),a produces hex D3 3F. Overwriting to 00 00 might do the trick. You’d expect to find it only twice, near the start of the ROM; if you find many then patching than all is likely to corrupt the game.


I appreciate the help but that does not appear to do anything. There are three instances of D3 3F in hex for "Zillion" for example. The changes do not seem to affect anything.
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Post Posted: Tue Jan 30, 2024 9:25 am
try looking for D3 3F DB DD and replace with D3 3F 3E FF the first time and D3 3F 3E 00 the second time... this should fool the detection

explanation: we're replacing
    out ($3f),a
    in a,($dd)
with
    out ($3f),a
    ld a,$ff
or with
    out ($3f),a
    ld a,$00
simulating the results an export system would give
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Post Posted: Tue Jan 30, 2024 4:57 pm
sverx wrote
try looking for D3 3F DB DD and replace with D3 3F 3E FF the first time and D3 3F 3E 00 the second time... this should fool the detection

explanation: we're replacing
    out ($3f),a
    in a,($dd)
with
    out ($3f),a
    ld a,$ff
or with
    out ($3f),a
    ld a,$00
simulating the results an export system would give


This absolutely WORKED!

Thank you, much appreciated! I have applied the patch to a few games and they work perfectly on a Japanese SMS in English.

I really appreciate the help!
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