Later SNES games also used a timing check to identify PAL vs NTSC clock frequencies. The mod I did nearly three decades ago was to add a toggle switch with a second crystal that would change the clock frequency and allow the PAL game to be played on an NTSC system. Wait a few seconds while the game booted up and then switch back and enjoy the unreleased in North America "Terranigma".
If I understand correctly, Terranigma was only released on PAL. Since you expected players would use an adapter you added a crystal in the cartridge so the timing would be the same NTSC system?
Did you also adjust the resolution to account for the missing tiles on NTSC?
The game that I cared about most when doing the mod was originally Japanese and then only released in the UK and Australia in English. So the resolution was NTSC compatible. I think there were some PAL exclusives, but I never ran into one that had an issue. Interesting question though!
Few console games of the era used the extra resolution so just ran squished[1] and letterboxed in the middle 480 lines. Most games tied game speed to frame rate, and didn't account for the fact that PAL systems ran at 50Hz instead of 60Hz, so just ran slower as well. Console gaming in Europe sucked until things like the Dreamcast that just took the brute force option of having a 60Hz output mode (and its now moot with HD where they only use 60Hz modes).
I doubt Terranigma had any optimisation, so would run just fine on an NTSC system.
[1] The width of the picture remained the same, just less height, so distortion.
I elaborated in a sibling comment, but my guess is that, since the game originated in Japan, which also was NTSC land, it was written to also work on NTSC to begin with.
Yes it was the sole driver for the mod, but I did end up getting a few other carts - Tintin, and I think a Dragon Ball game. I still have this modded SNES somewhere, I should pull it out and have a nostalgia fix.
The different frequency (field/frame rate) should be taken care of by having switched to the other crystal, the different resolution remains relevant. Not just that, there's also less time to perform computations while in vertical sync in NTSC compared to PAL. (Both those things are also related to the frequency of the crystal, by the way.)
But: Since the game originated in Japan, it was probably originally written for NTSC(-J) anyway, so my guess is that it makes use of neither the increased PAL resolution, nor the additional computation time.
Speaking as a UK SNES owner, there were a number of adaptors, and they seemed to support different games. A local games shop near me which did a lot of imports would encourage you to check your existing adaptor with new games, and offer to sell you a better adaptor if required.
The previous generation of the lockout chip on the NES is also a Sharp 4-bit MCU, but even more ancient. To save gates, the chip designers made it use an LFSR program counter. So, execution didn't go 00, 01, 02 at all. Had to be a real pain.
On the later SNES and then N64 iterations, they did use a standard incrementing PC, but still with the inscrutable opcodes. It was so arcane I had to write a special disassembler to spit out all the register operations while reversing it.
On the final (N64) iteration, these CICs actually support coexistence with multiple slave devices on the bus. They really had it down by then.
SF2 was such a disappointment when it was released on PAL SNES.
The game was expensive ($140AUD!) slower than the arcade and the graphics were squashed by black bars.
It was surreal to play a recent arcade game on console though and my action replay cart let me emulate the many “rainbow edition” versions on the game i.e modded arcade PCBs.
